Alkaline Phosphatase Test
Alkaline phosphatase is an enzyme found throughout the body. Like all enzymes, it is needed, in small amounts, to trigger specific chemical reactions. When it is present in large amounts, it may signify bone or liver disease or a tumor.
Alkaline phosphatase, or ALP, is an enzyme that removes phosphate groups from other biological molecules. It is present in all of your cells, but it is found in particularly high concentrations in your liver, bones, kidneys and intestines. During pregnancy, the placenta also produces large amounts of ALP. Different tissues produce slightly different types of ALP called "isoenzymes." Injury, inflammation or increased metabolic activity in any of the organs that produce ALP usually prompts an increase in the levels of this enzyme in your bloodstream.
If a blood test reveals an elevation in your ALP, your doctor may order additional examinations to see what triggered the elevation. The two most common sources of increased ALP levels are liver and bone, which produce different isoenzymes of ALP. According to "The Merck Manual of Diagnosis and Therapy," bone ALP can be differentiated from liver ALP by performing a heat fractionation test. However, this test is technically difficult, so other tests to check for liver problems are usually performed in lieu of heat fractionation. If these evaluations indicate that your liver is damaged, it is assumed that the ALP arose from your liver.
Your liver, particularly its bile ducts, is a rich source of ALP. When the cells in your liver are injured by infection, toxins or cancer, they release ALP and a variety of other enzymes into your blood. Obstruction of your bile ducts, which can occur with gallstones or tumors, often triggers striking elevations in your ALP levels. Additional blood tests, such as gamma-glutamyl transpeptidase or 5´-nucleotidase levels, help to determine whether ALP comes from your liver or from other tissues.
Any condition that increases the rate of bone metabolism or turnover will increase ALP blood levels. Rapid growth, healing fractures, Paget's disease, vitamin D deficiency, bone infections, hyperparathyroidism and bone cancers all cause the release of ALP into your bloodstream, where it can be measured. Sometimes the process responsible for a high ALP is obvious, so no further testing is done. However, because ALP is generated by so many tissues, an abnormally high level may mandate an exhaustive search for the cause when no obvious reason is present.
A normal ALP level varies from 20 to 140 IU/L, but normal ranges may vary among different laboratories. Although liver and bone are the most common sources of high ALP levels, other tissues and organs can cause elevations that may trigger an exhaustive and expensive medical evaluation. For example, your kidneys can release ALP into your bloodstream in response to injury, infection or cancer, but other signs of kidney damage may be absent. Occasionally, the cause of an abnormal ALP level eludes diagnosis.
Ribbon diagram (rainbow colored, N-terminus = blue, C-terminus = red) of the dimeric structure of bacterial alkaline phosphatase.
Alkaline phosphatase (ALP, ALKP) (EC 18.104.22.168) is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation. As the name suggests, alkaline phosphatases are most effective in an alkaline environment. It is sometimes used synonymously as basic phosphatase.In bacteria, alkaline phosphatase is located in the periplasmic space, external to the cell membrane. Since this space is much more subject to environmental variation than the actual interior of the cell, bacterial alkaline phosphatase is comparatively resistant to inactivation, denaturation, and degradation, and also has a higher rate of activity. Although the actual purpose of the enzyme is still not fully understood, the simple hypothesis that it is a means for the bacteria to generate free phosphate groups for uptake and use, is supported by the fact that alkaline phosphatase is usually produced by the bacteria only during phosphate starvation and not when phosphate is plentiful. However, other possibilities exist; for instance, the presence of phosphate groups usually prevents organic molecules from passing through the membrane, therefore dephosphorylating them may be important for bacterial uptake of organic compounds in the wild.Some complexities of bacterial regulation and metabolism suggest that other, more subtle, purposes for the enzyme may also play a role for the cell. In the laboratory, however, mutant Escherichia coli lacking alkaline phosphatase survive quite well, as do mutants unable to shut off alkaline phosphatase production.The optimal pH for the activity of the E. coli enzyme is 8.0 while the bovine enzyme optimum pH is slightly higher at 8.5.
Use in research:
Typical use in the lab for alkaline phosphatases includes removing phosphate monoester to prevent self-ligation.
Common alkaline phosphatases used in research include:
- Shrimp alkaline phosphatase (SAP), from a species of Arctic shrimp (Pandalus borealis)
- Calf-intestinal alkaline phosphatase (CIP)
- Placental alkaline phosphatase (PALP) and its C terminally truncated version that lacks the last 24 amino acids (constituting the domain that targets for GPI membrane anchoring) - the secreted alkaline phosphatase (SEAP)
Alkaline phosphatase has become a useful tool in molecular biology laboratories, since DNA normally possesses phosphate groups on the 5' end. Removing these phosphates prevents the DNA from ligating (the 5' end attaching to the 3' end), thereby keeping DNA molecules linear until the next step of the process for which they are being prepared; also, removal of the phosphate groups allows radiolabeling (replacement by radioactive phosphate groups) in order to measure the presence of the labeled DNA through further steps in the process or experiment. For these purposes, the alkaline phosphatase from shrimp is the most useful, as it is the easiest to inactivate once it has done its job.
Another important use of alkaline phosphatase is as a label for enzyme immunoassays.
Undifferentiated pluripotent stem cells have elevated levels of alkaline phosphatase on their cell membrane, therefore alkaline phosphatase staining is used to detect these cells and to test pluripotency (i.e. embryonic stem cells or embryonal carcinoma cells).
One common use in the dairy industry is as a marker of pasteurisation in cows' milk. This molecule is denatured by elevated temperatures found during pasteurisation, and can be tested for via colour change of a para-Nitrophenylphosphate substrate in a buffered solution (Aschaffenburg Mullen Test). Raw milk would typically produce a yellow colouration within a couple of minutes, whereas properly pasteurised milk should show no change. There are of course exceptions to this in the case of heat-stable alkaline phophatases produced by some bacteria.
Alkaline phosphatase is measured by combining the person's serum with specific substances with which alkaline phosphatase is known to react. The end product of this reaction is measured; and from that measurement, the amount of alkaline phosphatase in the person's serum is determined.
Each tissue—liver, bone, placenta, and intestine—produces a slightly different alkaline phosphatase. These variations are called isoenzymes. In the laboratory, alkaline phosphatase is measured as the total amount or the amount of each of the the four isoenzymes. The isoenzymes react differently to heat, certain chemicals, and other processes in the laboratory. Methods to measure them separately are based on these differences.
The test is covered by insurance when medically necessary. Results are usually available the next day. Alkaline phosphatase (ALP) is a protein found in all body tissues. Tissues with particularly high amounts of ALP include the liver, bile ducts, and bone. A blood test can be done to measure the level of ALP.
Alkaline phosphatase (ALP) is a substance found in all body tissues. There are many different forms of ALP. Each type is different and is called an isoenzyme. Its structure depends on where in the body it is produced, such as the liver and bones. This test measures the amount of alkaline phosphatase (ALP) in blood. It is used to evaluate bone disease and liver disease.
An alkaline phosphatase in blood test is usually used to gauge the levels of the enzyme alkaline phosphatase in the body. While the normal values of the enzyme may vary from lab to lab, the generally accepted standards read at about 30 to 126 units per liter in adults and about 30 to 300 units per liter in children. Women that are in the third trimester of a pregnancy will tend to have higher levels of alkaline phosphatase because the placenta is a major producing agent of the enzyme. Higher levels of the enzyme that are of more concern are usually the result of liver problems such as hepatitis, gallstones, liver cancer, cirrhosis and cancer that has spread to the liver from another part of the body. Bone diseases such as Paget's disease, rickets and bone tumors can also have a significant contribution to heightened alkaline phosphatase levels. Low alkaline phosphatase blood test will usually be a sign of malnutrition and like celiac disease or a lack of nutrients such as scurvy.
Alkaline Phosphatases are a group of enzymes found primarily the liver (isoenzyme ALP-1) and bone (isoenzyme ALP-2). There are also small amounts produced by cells lining the intestines (isoenzyme ALP-3), the placenta, and the kidney (in the proximal convoluted tubules). What is measured in the blood is the total amount of alkaline phosphatases released from these tissues into the blood. As the name implies, this enzyme works best at an alkaline pH (a pH of 10), and thus the enzyme itself is inactive in the blood. Alkaline phosphatases act by splitting off phosphorus (an acidic mineral) creating an alkaline pH.
The primary importance of measuring alkaline phosphatase is to check the possibility of bone disease or liver disease. Since the mucosal cells that line the bile system of the liver are the source of alkaline phosphatase, the free flow of bile through the liver and down into the biliary tract and gallbladder are responsible for maintaining the proper level of this enzyme in the blood. When the liver, bile ducts or gallbladder system are not functioning properly or are blocked, this enzyme is not excreted through the bile and alkaline phosphatase is released into the blood stream. Thus the serum alkaline phosphatase is a measure of the integrity of the hepatobiliary system and the flow of bile into the small intestine.
In addition to liver, bile duct, or gallbladder dysfunction, an elevated serum alkaline phosphatase can be due to rapid growth of bone since it is produced by bone-forming cells called osteoblasts. One would expect that growing children have higher levels than full-grown adults. The relationship of alkalinity to bone development warrants further discussion because it plays a major role in the prevention and reversal of osteoporosis. Just as calcium builds up around faucets, so is calcium laid down into bone. The reason the calcium deposits on your faucet is because the water is alkaline and calcium comes out of solution and crystallizes in an alkaline environment. The reverse is also true, "Lime -Away", vinegar, or any other acidic solution dissolve the calcium deposits because they are acidic. It makes sense that osteoblasts by creating a local environment of alkalinity via alkaline phosphatase helps build bone. It also implies that in order to slow bone loss, one can not be in an acidic state. Studies have shown that giving bicarbonate of potassium is just as effective as calcium in correcting osteoporosis! One would expect then that in an acidic state, the body will compensate for this by increasing the bone alkaline phosphatase levels.
Because acid-alkaline is influenced by many other glands, the implications of serum alkaline phosphatase levels must consider more than just bone and liver function. Associated organs/glands include adrenals, uterus, prostate, and intestine.
The consequences of impaired bile flow are pervasive since bile is critical to your body's ability to process fats. As a result, fats remain undigested in the digestive tract and can cause bloating, cramps, light colored stools, gaseousness, etc. especially after a rich food. Many patients report pressure or pain in the right upper area of their abdomen where the liver and gallbladder are located. You may have discomfort in the right shoulder or between your shoulder blades anywhere from your mid-back to the base of your neck. Many people say they "carry my stress in the upper back and neck." This may due to gallbladder dysfunction. Unfortunately, a normal alkaline phosphatase does not exclude hepatobiliary dysfunction. In many cases, even the ultrasound shows no gallstones, etc. Rather the problem is that the bile does not flow freely throughout the system, which may result in insufficient bile action.
The consequences of impaired bile function involve the endocrine system in a major way because all of the steroid hormones are metabolized in part by the liver. These include the sex hormones (androgens and estrogens). As a result the menstrual cycle, sexual functions and sex characteristics can be affected.
Alkaline phosphatase (ALP) is present in a number of tissues including liver, bone, intestine, and placenta. The activity of ALP found in serum is a composite of isoenzymes from those sites and, in some circumstances, placental or Regan isoenzymes. Serum ALP is of interest in the diagnosis of 2 main groups of conditions-hepatobiliary disease and bone disease associated with increased osteoblastic activity.
A rise in ALP activity occurs with all forms of cholestasis, particularly with obstructive jaundice. The response of the liver to any form of biliary tree obstruction is to synthesize more ALP. The main site of new enzyme synthesis is the hepatocytes adjacent to the biliary canaliculi.
ALP also is elevated in disorders of the skeletal system that involve osteoblast hyperactivity and bone remodeling, such as Paget's disease rickets and osteomalacia, fractures, and malignant tumors.
Moderate elevation of ALP may be seen in other disorders such as Hodgkin's disease, congestive heart failure, ulcerative colitis, regional enteritis, and intra-abdominal bacterial infections.
Medical testing of alkaline phosphatase is concerned with the enzyme that is found in liver, bone, placenta, and intestine. In a healthy liver, fluid containing alkaline phosphate and other substances is continually drained away through the bile duct. In a diseased liver, this bile duct is often blocked, keeping fluid within the liver. Alkaline phosphatase accumulates and eventually escapes into the bloodstream.
The alkaline phosphatase of the liver is produced by the cells lining the small bile ducts (ductoles) in the liver. Its origin differs from that of other enzymes called aminotransferases. If the liver disease is primarily of an obstructive nature (cholestatic), i.e. involving the biliary drainage system, the alkaline phosphatase will be the first and foremost enzyme elevation. If, on the other hand, the disease is primarily of the liver cells (hepatocytes), the aminotransferases will rise prominently. Thus, these enzymes are very useful in distinguishing the type of liver disease-cholestatic or hepatocellular.
Growing bones need alkaline phosphatase. Any condition of bone growth will cause alkaline phosphatase levels to rise. The condition may be normal, such as a childhood growth spurt or the healing of a broken bone; or the condition may be a disease, such as bone cancer, Paget's disease, or rickets.
During pregnancy, alkaline phosphatase is made by the placenta and leaks into the mother's bloodstream. This is normal. Some tumors, however, start production of the same kind of alkaline phosphatase produced by the placenta. These tumors are called germ cell tumors and include testicular cancer and certain brain tumors.
Alkaline phosphatase from the intestine is increased in a person with inflammatory bowel disease, such as ulcerative colitis.
Blood is made up of two parts:
- Fluid (plasma or serum)
Plasma contains various substances including glucose, electrolytes, proteins, and water. Serum is the fluid part that remains after the blood is allowed to clot in a test tube. Specifically, serum is the fluid part of blood after a substance called fibrinogen has been removed by clotting.
Cells in the blood include red blood cells, white blood cells, and platelets. Blood helps move oxygen, nutrients, waste products, and other materials through the body. It helps control body temperature, fluid balance, and the body's acid-base balance. Tests on blood or parts of blood may give your doctor important clues about your health.
A blood test alkaline phosphatase is performed to check for any liver disease or damage to the liver. It may also be used to identify any damage being caused to liver by the administration of certain medications. The test is also commonly used to follow up and check on the effectiveness of certain treatments such as in the case of Paget's disease. When there is evidence of liver disease accompanied by high alkaline phosphatase levels, this is generally a sign of blocked bile ducts. The heightened levels of ALP will often allow any cancer to spread to the liver or bones and a blood test alkaline phosphatase will help identify if this has already happened. In most labs, the test is usually a part of a routine set of tests known as the liver panel. If the doctor is unsure of the cause of the heightened Alp levels, a ALP isoenzyme test may also be ordered.
This test is done to diagnose liver or bone disease, or to see if treatments for those diseases are working. It may be included as part of a routine liver function test.
Common tests that are used to evaluate how well the liver is working (liver function) include:
- Alpha-1 antitrypsin
- Gamma-glutamyl transpeptidase (GGT)
- Prothrombin time
- Serum bilirubin
- Urine bilirubin
An alkaline phosphatase (ALP) test measures the amount of the enzyme ALP in the blood. ALP is made mostly in the liver and in bone with some made in the intestines and kidneys. It also is made by the placenta of a pregnant woman.
The liver makes more ALP than the other organs or the bones. Some conditions cause large amounts of ALP in the blood. These conditions include rapid bone growth (during puberty), bone disease (osteomalacia or Paget's disease), or a disease that affects how much calcium is in the blood (hyperparathyroidism), vitamin D deficiency, or damaged liver cells.
If the ALP level is high, more tests may be done to find the cause.
A test for alkaline phosphatase (ALP) is done to:
- Check for liver disease or damage to the liver. Symptoms of liver disease can include jaundice, belly pain, nausea, and vomiting. An ALP test may also be used to check the liver when medicines that can damage the liver are taken.
- Check bone problems (sometimes found on X-rays), such as rickets, osteomalacia, bone tumors, Paget's disease, or too much of the hormone that controls bone growth (parathyroid hormone). The ALP level can be used to check how well treatment for Paget's disease or a vitamin D deficiency is working.
Alkaline phosphatase (often shortened to alk phos) is an enzyme made in liver cells and bile ducts. The alk phos level is a common test that is usually included when liver tests are performed as a group.
To collect the 5-10 ml blood needed for this test, a healthcare worker ties a tourniquet on the person's upper arm, locates a vein in the inner elbow region, and inserts a needle into that vein. Vacuum action draws the blood through the needle into an attached tube. Collection of the sample takes only a few minutes.
Since an alkaline phosphatase in blood test is usually taken around the time of a routine blood test, no special preparation is required. However, if you are undergoing a follow up ALP test, you may be asked to avoid consumption of any food or drink for about 10 hours prior to the test. This is mainly because of the fact that the ALP levels are generally higher after eating - especially if the meal consisted of a lot of fatty foods. Moreover, it is essential that you also let your doctor know of any medication you are on, prescription or nonprescription, as a number of them have the ability to alter your test results.
You should not to eat or drink anything for 6 hours before the test, unless otherwise instructed by your doctor.
Many drugs affect the level of alkaline phosphatase in the blood. Your health care provider may tell you to stop taking certain drugs before the test. Never stop taking any medicine without first talking to your doctor. Drugs that may affect the ALP level may include:
- Birth control pills
- Certain diabetes medicines
- Male hormones
- Narcotic pain medicines
- Nonsteroidal anti-inflammatory drugs (NSAIDs), used for arthritis and pain)
- Tricyclic antidepressants
A person being tested for alkaline phosphatase should not have anything to eat or drink, except water, for eight to ten hours before the test. Some people release alkaline phosphatase from the intestine into the bloodstream after eating. This will temporarily increase the result of the test.
Discomfort or bruising may occur at the puncture site or the person may feel dizzy or faint. Pressure to the puncture site until the bleeding stops will reduce bruising. Warm packs to the puncture site will relieve discomfort.
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
How you prepare depends on the specific blood test you are having done. Many tests do not require any special preparation. Other times, you may be told to avoid food or drinks or limit certain medications before the test.When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.
An alkaline phosphatase test is often done at the same time as a routine blood test. You do not need to do anything before having a routine blood test.
If you are having a follow-up ALP test, you may be asked to not eat or drink for 10 hours before the test. The ALP level generally goes up after eating, especially after eating fatty foods.
Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
The health professional drawing your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure to the site and then a bandage.
Normal results vary by age and by sex. They also vary based on the laboratory and the method used.
The normal range is 44 to 147 IU/L (international units per liter).
Normal values may vary slightly from laboratory to laboratory. They also can vary with age and gender. High levels of ALP are normally seen in children undergoing growth spurts and in pregnant women. The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
An alkaline phosphatase (ALP) test measures the amount of the enzyme ALP in the blood.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Adults: 25–100 units per liter (U/L) or 0.43–1.70 microkat/liter (mckat/L)
Children: Less than 350 U/L or less than 5.95 mckat/L
Women in the third trimester of pregnancy have high ALP levels because the placenta makes ALP. Children normally have much higher ALP than adults because rapid bone growth is normal in children and bones make ALP.
The optimal range for alkaline phosphatase depends on your age. A growing adolescent will have a much higher alkaline phosphatase than a full grown adult because his/her osteoblasts are laying down bone very rapidly. For an adult, 50-75 mg/dl is considered a reasonable optimal range.
An increased serum Alkaline Phosphatase may be due to:
Congestion or obstruction of the biliary tract, which may occur within the liver, the ducts leading from the liver to the gallbladder, or the duct leading from the gallbladder through the pancreas that empty into the duodenum (small intestine). Any of these organs (liver, gallbladder, pancreas, or duodenum) may be involved.
- Oral contraceptives
- Obstructive pancreatitis
- Congestive heart failure
- Malignancy involving liver
- Paget's Disease
- Herpes Zoster (Shingles)
- Over-activity of the Parathyroid glands (Primary Hyperparathyroidism, Secondary Hyperparathyroidism from kidney disease, osteomalacia, malabsorption)
- Rickets - Vitamin D deficiency
- Healing fractures, rapid bone growth Rapid bone growth such as after a fracture, bone cancers like osteogenic sarcoma, Osteomalacia, and Paget's Disease.
- Osteoporosis treatment
- Adrenal cortical hyperfunction
- As a normal part of late pregnancy since the placenta produces alkaline phosphatase (placenta - ~2x normal)
- Granulation tissue
- Gastrointestinal inflammation (Inflammatory Bowel Disease: Ulcerative colitis, Crohn’s; ulcers)
- Systemic infections (sepsis)
- Rheumatoid arthritis.
- Certain cancers such as Hodgkin's Lymphoma, gynecologic malignancies.
- Acute tissue damage in the heart or lungs (myocardial or pulmonary infarctions).
An elevated alkaline phosphatase almost always requires other tests to determine the origin of the condition. For example, liver enzyme tests to check the integrity of the liver, x-rays or other bone images if a bone abnormality is evident. Although not used often, the isoenzyme profile of alkaline phosphatases can be determined to see if the elevation of alkaline phosphatase came primarily from liver (ALP-1), bone (ALP-2), or elsewhere. Most often, however there is a modest elevation from ideal but the actual value is within the laboratories reference range and the origin is inferred from the symptoms, exam, or existing lab results.
A decreased serum alkaline phosphatase may be due to:
- Zinc deficiency.
- Vitamin C deficiency/Scurvy.
- Folic acid deficiency.
- Excess Vitamin D intake.
- Low phosphorus levels (hypophosphatasia)
- Celiac disease.
- Malnutrition with low protein assimilation (including low stomach acid production/hypochlorhydria).
- Insufficient Parathyroid gland function.
- Pernicious anemia
- Vitamin B6 insufficiency
Explanation of test results:
A high alk phos level does not reflect liver damage or inflammation. A high alk phos level occurs when there is a blockage of flow in the biliary tract or a buildup of pressure in the liver--often caused by a gallstone or scarring in the bile ducts.
Other things to know:
- Many patients with hepatitis C have normal alk phos levels.
- Hepatitis C treatment usually does not affect alk phos levels.
- Alk phos is produced in other organs besides the liver--it is also found in the bones and the kidneys.
- If your alk phos level is high, your doctor will probably order additional tests to determine why.
Below is the Age wise Reference Values:
4 years: 149-369 U/L
5 years: 179-416 U/L
6 years: 179-417 U/L
7 years: 172-405 U/L
8 years: 169-401 U/L
9 years: 175-411 U/L
10 years: 191-435 U/L
11 years: 185-507 U/L
12 years: 185-562 U/L
13 years: 182-587 U/L
14 years: 166-571 U/L
15 years: 138-511 U/L
16 years: 102-417 U/L
17 years: 69-311 U/L
18 years: 52-222 U/L
> or =19 years: 45-115 U/L
4 years: 169-372 U/L
5 years: 162-355 U/L
6 years: 169-370 U/L
7 years: 183-402 U/L
8 years: 199-440 U/L
9 years: 212-468 U/L
10 years: 215-476 U/L
11 years: 178-526 U/L
12 years: 133-485 U/L
13 years: 120-449 U/L
14 years: 153-362 U/L
15 years: 75-274 U/L
16 years: 61-264 U/L
17-23 years: 52-144 U/L
24-45 years: 37-98 U/L
46-50 years: 39-100 U/L
51-55 years: 41-108 U/L
56-60 years: 46-118 U/L
61-65 years: 50-130 U/L
> or =66 years: 55-142 U/L
Reference values have not been established for patients that are <4 years of age.
ALP elevations tend to be more marked (more than 3-fold) in extrahepatic biliary obstructions (eg, by stone or cancer of the head of the pancreas) than in intrahepatic obstructions, and the more complete the obstruction, the greater the elevation. With obstruction, serum ALP activities may reach 10 to 12 times the upper limit of normal, returning to normal upon surgical removal of the obstruction. The ALP response to cholestatic liver disease is similar to the response of gamma-glutamyltransferase (GGT), but more blunted. If both GGT and ALP are elevated, a liver source of the ALP is likely.
Among bone diseases, the highest level of ALP activity is encountered in Paget's disease, as a result of the action of the osteoblastic cells as they try to rebuild bone that is being resorbed by the uncontrolled activity of osteoclasts. Values from 10 to 25 times the upper limit of normal are not unusual. Only moderate rises are observed in osteomalacia, while levels are generally normal in osteoporosis. In rickets, levels 2 to 4 times normal may be observed. Primary and secondary hyperparathyroidism are associated with slight to moderate elevations of ALP; the existence and degree of elevation reflects the presence and extent of skeletal involvement. Very high enzyme levels are present in patients with osteogenic bone cancer. A considerable rise in ALP is seen in children following accelerated bone growth.
ALP increases of 2 to 3 times normal may be observed in women in the third trimester of pregnancy, although the reference interval is very wide and levels may not exceed the upper limit of normal in some cases. In pregnancy, the additional enzyme is of placental origin.
Bone and liver disease increase alkaline phosphatase more than any other disease, up to five times the normal level. Irritable bowel disease, germ cell tumors, and infections involving the liver, such as viral hepatitis and infectious mononucleosis, increase the enzyme also, but to a lesser degree. Healing bones, pregnancy, and normal growth in children also increase levels.
Higher-than-normal ALP levels may be due to:
- Biliary obstruction
- Bone disease
- Eating a fatty meal if you have blood type O or B
- Healing fracture
- Liver disease
- Osteoblastic bone tumors
- Paget's disease
Lower-than-normal ALP levels (hypophosphatasemia) may be due to:
- Protein deficiency
- Wilson's disease
Additional conditions under which the test may be performed:
- Alcoholic liver disease (hepatitis/cirrhosis)
- Biliary stricture
- Giant cell (temporal, cranial) arteritis
- Multiple endocrine neoplasia (MEN) II
- Renal cell carcinoma
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
There is very little chance of a problem from having blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
Reasons you may not be able to have the test or why the results may not be helpful include:
- Taking medicines that may damage the liver, such as some antibiotics, birth control pills, long-term aspirin use, and oral diabetes medicines.
- Being pregnant. Women in the third trimester of pregnancy have high ALP levels because the placenta makes ALP.
- Going through menopause. Postmenopausal women may have higher ALP levels than women who still have menstrual cycles.
- Your age. Children normally have much higher ALP levels than adults because rapid bone growth is normal in children and bones make ALP.
- Drinking a lot of alcohol.
Very high levels of ALP can be caused by liver problems, such as hepatitis, blockage of the bile ducts (obstructive jaundice), gallstones, cirrhosis, liver cancer, or cancer that has spread (metastasized) to the liver from another part of the body.
High ALP levels can be caused by bone diseases, such as Paget's disease, osteomalacia, rickets, bone tumors, or tumors that have spread from another part of the body to the bone, or by overactive parathyroid glands (hyperparathyroidism). Normal healing of a bone fracture can also raise ALP levels.
Heart failure, heart attack, mononucleosis, or kidney cancer can raise ALP levels. A serious infection that has spread through the body (sepsis) can also raise ALP levels.
Conditions that lead to malnutrition (such as celiac disease) or are caused by a lack of nutrients in the diet (such as scurvy) can cause low ALP levels.
What To Think About
If the ALP level is high, other tests may be done to determine whether a liver or bone problem is present.
If liver disease is suspected, more blood tests, an ultrasound, or a CT scan are generally recommended to find the problem.
Other tests to check liver function, such as alanine aminotransferase, aspartate aminotransferase, and bilirubin, are often done at the same time as an alkaline phosphatase (ALP) test. For more information, see the medical tests Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), and Bilirubin.
Gamma glutamyl transferase (GGT), or gamma glutamyl transpeptidase, may be measured in the blood to check the difference between bone ALP and liver ALP. High levels of GGT are present when the liver is damaged but not present with bone disease. A high level of GGT may be caused by alcohol use or may mean that blocked bile ducts are causing inflammation. The level of GGT may be high with the use of certain medicines, such as phenytoin and phenobarbital. In some medical centers, a test that measures a substance called 5-nucleotidase is done instead of the GGT test because it is better at finding liver disease.