Serum Creatinine Test is the most common method used to measure the Kidney function. The Serum creatinine has utmost important role in medical diagnosis as it acts as an indicator of GFR or glomerular filtration rate which is an expression of the quantity of glomerular filtrate formed each minute in the nephrons of both kidneys, usually measured by the rate of clearance of creatinine and is based on constant production from muscle creatine and constant excretion rate from Kidneys. Everyday 1-2% Creatine present in the muscles gets transformed into Creatinine which is approximately 15-30 mg creatinine/Kg weight. The quantity of Creatinine formed is directly related with the muscle mass in the body. The removal of Creatinine takes place from plasma by Glomerular filtration rate which is then removed out of the body through excretion and no major tubular reabsorption is seen of it.
The Serum Creatinine test is a crude indicator of the disease pertaining to the Kidney. The Creatinine levels in the serum may not likely detect the moderate changes in GFR.A change in the serum Creatinine level from 0.6 to1.2 mg/dL will indicate 50% decline in GFR even though creatinine level is in normal levels. A serum Creatinine level of 1.2 mg/dL can be of no clinical significance if an earlier baseline Creatinine is not present for the comparison purpose.
People with muscle disease, cachexia which is weight loss, small heighted individual or with amputations have decreased level of Serum creatinine. It is seen that during certain advanced liver disease, decrease in the serum creatinine levels take place due to decrease in the hepatic conversion of Creatine to Creatinine. Other than that serum creatinine is seen to fall due to decreased dietary protein intake, rise renal tubular secretion of creatinine and muscle wasting it is seen that patients with certain liver disease can have normal levels of serum creatinine even if the creatinine clearance is less than 60 mL/min.
In aged people the Creatinine production is decreased as they have decreased muscle mass. An increased GFR is seen during pregnancy which causes the fall in the level of Creatinine levels in the body. A sudden loss of Kidney function which occurs over several hours to days is known as acute renal failure. Increased serum creatinine concentrations more than 0.5 mg/dL, decline in urinary output, a 50% increase of serum creatinine levels and accumulation of nitrogenous wastes or >25% decline in creatinine clearance are the main indicators of the Acute Renal Failure.
The increased Serum creatinine takes place when the Glomerular filtration rate is decreased. The reasons behind the High Creatinine levels is attributed to conditions such as intrinsic renal disease, reduced renal blood flow from congestive heart failure, urinary tract obstruction or shock/dehydration. When there is acute renal failure, serum creatinine is seen l rising 1 to 2 mg/dL per day.
- If the rate by which this rise takes place is less, then it is an indicator of residual renal function existence.
- If the rise in the levels is greater than 3 mg/dL per day indicates the presence of increased catabolism or skeletal muscle.
- The condition of Rhabdomyolysis which is an acute, fulminant, potentially fatal disease that destroys skeletal muscle can also lead to rise in the levels of serum creatinine.
If the rate of rise exceeds, the rise in the Creatinine is comparatively slower than rise in Blood Urea Nitrogen In patients suffering from reduced renal blood
The formula used for the calculation of Creatinine clearance from the serum creatinine is
Creatinine clearance= weight x (140 - age)/72 x serum creatinine
Creatinine clearance = weight x (140 - age) x 0.85/72 x serum creatinine
To determine the origin of the acute renal failure, the ratio of BUN to creatinine is considered.
The normal ratio Of BUN to Creatinine is 10: 1. This ratio is seen to exceed 20 in conditions of prerenal failure which takes place due to decreased renal perfusion which is also seen in certain condition such as hypertension, haemorrhage, or dehydration.
Certain Postrenal (pertaining to those parts of the urinary system that, anatomically and physiologically, are distal to the kidney) diseases like urinary tract obstruction also increase the BUN to Creatinine ratio between 10 and 20.
The ratio of I (10 :12) is considered normal in intrinsic renal disease because BUN and creatinine levels rise proportionately The clinical usefulness of this ratio becomes limited by nonrenal factors which increase the Blood Urea Nitrogen such as Gastrointestinal bleeding, parenteral nutrition which is administration of nutriment intravenously or during glucocorticoid therapy. The Gastrointestinal bleeding increases BUN more compared to creatinine because of increased amino acid absorption from digested blood and hypovolemia which is diminished volume of circulating blood in the body.
0.9 – 1.3
0.6 – 1.3
0.6 – 1.1
0.4 – 1.1
The original equation to determine Glomelular filtration rate was developed by modifying the diet in condition of Renal disease study using the using the older creatinine methods with a slight positive
The low values of Creatinine measurements is generally seen in paediatric (pertaining to health of children) patients as they have greater variability in the levels than for values seen in adults. For the estimation of kidney function, based on these values likely show greater variability than in adults.
The Normal range for Creatinine in Urea is
Male 0.8 – 2.0 g/24 hour
Female 0.6 – 1.8 g/24 hour
In certain conditions such as Impaired renal function, Shock, Muscle diseases such as gigantism, acromegaly which is abnormal enlargement of limbs, and myasthenia gravis which is an autoimmune disease that causes muscle weakness, Urinary tract obstruction or Chronic nephritis, the increased in Serum Creatinine levels is seen.
Decreased creatinine levels may be seen in aged person, persons with small stature or having decreased muscle mass or during inadequate dietary protein. Muscle atrophy known as decrease in the mass of the muscle can also result in decreased in the level of serum creatinine. If any type of muscle atrophy is detected the monitoring of serum Creatine which is an important enzyme required for the normal muscle functioning.
A condition where the level of serum creatinine level determination is important is when there is a damage to a large number of nephrons. The serum creatinine level is not affected by hepatic protein metabolism as it’s seen during the Blood Urea Nitrogen. (BUN)The tests which measures creatinine of serum, urine and creatinine clearance are all used exclusively for the evaluation of the Functioning of the Kidneys. Any dysfunction in the Kidneys will definitely change the results of the test. The rise in Serum creatinine level will happen only when the half of nephrons present in the kidney becomes dysfunctional due to damage of these nephrons. It is seen that the rise and fall in the levels of Creatinine is comparatively slower than the levels of Blood Urea Nitrogen levels so because of this reason Creatinine levels are mostly preferred to diagnose the effective Kidney function.
The Blood Creatinine Levels
The Creatinine is present in the body in tissues of muscles. In the human body constant breakdown and rebuilt of this substance by the protein fibres is essential for the strong and healthy maintenance of the muscles. The secondary result of this process results in the production of Creatinine levels in the body.
The Kidneys play an important role in removing creatinine from the body and it denotes the efficient working of the Kidneys. But any dysfunction of the Kidneys may lead to higher than normal levels of Creatinine in the body. In such scenario the doctor can for a blood test to check the levels of Creatinine in the body of the patient.
What is the normal level of Creatinine in the body?
The level of Creatinine in the blood depends on mass of the muscles and even the gender of the person. The normal value comes around to be 0.8 to 1.4 mg/dL. But in sportsmen and athletes the level of the Creatinine is seen higher than normal individual which are around 1.8 mg/dL as these people have more muscle mass for the breakdown which increases the Creatinine levels. The reason for Women having lower Creatinine levels is attributed to the low muscle mass in the body as compared with their male counterparts.
What Symptoms call for the Serum Creatinine test?
The doctor can order the Creatinine test as a part of the Basic metabolic test. The most common symptoms associates with the disease of Kidneys are as follows:
- Lack of energy, feelings of muscle weakness(Fatigue)
- Foamy/Frothy urination
- Trouble in sleeping
- Body swelling
- Pain in the back of the body specially the mid back
- High BP(Blood pressure)
But in certain cases it is seen that symptoms do not appear but then also the Creatinine levels come out abnormal.
What are the Abnormal Results?
If the level of Blood Creatinine levels goes beyond 2.0 mg/dL then it is considered a sign to worry as this level will suggest that the filtration of the Creatinine out of the body is not effectively done by the Kidneys.
A higher level of Creatinine is suggestive of various diseases such as eclampsia (convulsions and coma) Muscular dystrophy (in which strength and muscle bulk gradually decline), dehydration, kidney failure, Glomerulonephritis (inflammation of the glomerular, bundles of tiny vessels inside the kidneys) or urinary tract obstruction.
Abnormal results doesn’t only mean higher than normal but can also be lower than the required amounts.
This can happen due to excessive breakdown of the muscles cells in the body. Some other conditions which also results in the lowering of the levels of Creatinine are muscular dystrophy and myasthenia gravis a disease that causes muscle weakness. Any abnormal result is subjected to further testing so as the doctor can accurately determine the medical condition of the person.
What are the other additional uses of this test?
Apart from serving as a tool for the diagnosis these levels can also be used to determine the effect of certain medications for the effective functioning of the kidneys.
A fall in the creatinine level is suggestive that the medication is doing its job effectively.
If a person undergoes the process of dialysis the Creatinine can be a useful test to determine the effectiveness of the dialysis treatment.
During the metabolism process which is the complex physical and chemical processes occurring within a living cell or organism that are necessary for the maintenance of life the Creatinine is formed when the food gets converted into energy. The Creatinine and Creatinine clearance test is useful to check the level of Creatinine in the blood and urine of a person. These tests play an effective role in determining the proper functioning of the Kidneys. The breakdown product of creatine is Creatinine which comes out of the blood by Kidneys and is passed outside the human body through urination process. The diet of a person or any normal physical activities is not seen to hamper the level of Creatinine in the human body .The dysfunction or the damage of the kidneys will hamper the proper working of the Kidneys which in turn leads to the rise in the level of Creatinine in the blood while fall in the level of the substance in the urine of the body.
The types of Creatinine test are as follows:
Blood creatinine level
The Creatinine levels in the blood are indicative of the proper working of the kidneys. A rise in the level indicates that the kidneys are not working properly. The level of creatinine in the blood depends on the mass of muscle tissue and it is seen that generally men have higher levels of Creatinine than the female counterparts due to the more muscle mass in men than women.
Creatinine clearance test
This test is done on a sample of both blood and 24 hour urine sample, and it is used to determine how well the substance Creatinine is removed from both the blood/Kidneys. This test is gives a better idea than the Creatinine test to determine the proper working of the kidneys.
What Is BUN?
BUN/Creatinine ratio is used for the determination of the level of the Creatinine and Blood Urea Nitrogen and is an effective tool which can aid the physicians for problems related with Dehydration or the loss of water and salts essential for normal body function which leads to the abnormal rise in the level of creatinine or the Blood Nitrogen Urea levels in the body.
The breakdown of protein results in the formation of a waste product called Urea in the human body. The Urea is manufactured in the Liver and is excreted out of the body through Urine. The BUN test is useful in determining the amount of Urea present in the blood .Just like the Creatinine test can help the physician in determining the proper working of the Kidneys.
The breakdown of Creatine results in the formation of Creatinine, a part of the cells of muscles in the body. The measurement of Creatinine can also be done by testing the sample of Urine in the body.
This test is deployed to examine the amount of Creatinine a waste product in the blood sample of a person. Apart from that this test is effective to determine the proper working of the Kidneys in the human body. The metabolism of proteins results in the formation of Creatine which on further breakdown forms Creatinine. The kidneys act as a filter by remove the Creatinine from the body through the Urine. Any disease /damage to the Kidney can lead to the rise in the level of Creatinine in the blood and a decreased level in the Urine of a person.
The Creatinine test is basically done to determine whether the kidneys are working properly or not .This test is also important to monitor the progress of a renal disease and to assess the response shown by the patient to the treatment of the kidney disease. This test can also be useful in determining if a person is suffering from Dehydration.
The BUN to creatinine ratio also helps in identifying whether the person suffers from any renal disease or dehydration (loss of water and salts essential for normal body function.)
The ratio can also be used to check the renal toxicity in patients who are likely to be affected to Kidney damage or are on certain medications which can affect the working of the Kidneys severely.
It is advised not to indulge in any vigorous exercise for minimum 2 days prior to the test. The intake of food rich in protein like fish, eggs or meat should be restricted for minimum one day prior to the test. Fluid intake should be adequate but consumption of tea, coffee should be avoided as they contribute to urine formation and loss of salts from the body of a person.
The normal values of the test change from lab to lab which depends upon the apparatus and its use during calibration purpose. But generally the normal creatinine levels in the blood lies within 0.7 and 1.2 milligrams per deciliter (mg/dL).
The normal range of creatinine clearance lies between 90 and 140 millilitres per minute (mL/min).
If the level of Creatinine in the blood is high it indicates serious kidney damage/dysfunction. Other than that higher Creatinine clearance can also take place during conditions such as vigorous exercise, carbon monoxide poisoning, burns or injury to the muscle cells in the body.
A higher BUN/Creatinine ratio depicts any renal (Kidney) damage or bleeding in the respiratory/digestive tract of a person. It is advisable that the urine sample should be kept free from hair,stool,menstrual blood or any type of foreign matter so that the results of the test comes to be accurate and is not altered by these substances.
This test is generally free from any major complications but it is seen that the improper blood collection or clearance of the punctured site can lead to inflammation, bruising etc.
In early days methods were explored for measuring, creatinine plasma and serum. But in today’s time use of Jaffe reaction for determining creatinine level in blood, using alkaline picrate is one of the most reliable methods, which helps in overcoming the challenges of analytical interferences. Nowadays as projected eGFR (glomerular filtration rate) rate can be determined, inter-laboratory arrangement of serum creatinine results has turned out to be of top priority.
The clinical biochemists should have a thorough knowledge about the relative performance of the daily creatinine methods. The Creatinine test is also known as Serum Creatinine.
The role of Creatinine is important for the determination of the Kidney (Renal) function because of the several properties it possess which is useful for the determining the test. The Creatinine levels in the blood is an indicator of GFR (Glomerular Filtration Rate) while in Urine it can used as a quality assurance tool and will eradicate the necessity for 24-hour collections.
Following are the normal reference range for the serum creatinine and urine creatinine.
In males: 0.5–1.2 mg/dL
In females: 0.4 – 1.1 mg/dL
Infants/Children up to 12years-0.0–0.7 mg/dL
The variation of the reference range is seen with difference in race, gender and ethnicity of an individual. In order to actively determine/monitor the Kidney function one should look upon the calculated estimated glomerular filtration rate which is measured from the serum creatinine .The creatinine clearance can also be used for determining the GFR level.
- Males: 20-25 mg/kg/day
- Females: 15-20 mg/kg/day
As the concentrations of Urine Creatinine changes with the water intake in body, they are not very useful to determine the creatinine levels.
The presence of Low Serum Creatinine values is less often seen as it is the indicator of lower mass of the muscles in the body. Theoretically lower values can also be attributed with the increased in the GFR or glomerular Filtration rates.
During acute or chronic renal/Kidney damage a rise in Creatinine along with the fall in the GFR is seen.
The rise in serum creatinine is very less during the primary stage of the disease.
The difference in the muscle mass varies from person to person depending upon the age,race.gender and ethnicity .Keeping this factor in mind most labs measure GFR along with the Serum Creatinine for patients above the age of 18 years. The eGFR is responsible for some variables which can help physician to be aware of the reductions in the GFR even if the creatinine levels in the serum comes to be normal or slightly raised than normal.
These calculations are considered void in patients who belong to the group like children/aged/pregnant or are suffering from malnutrition, paraplegia, patients suffering from disease of the skeletal muscles or in those where the Kidney functions change rapidly.
As the muscle mass varies from person to person the use of only one reference range cannot bring accurate results .A serum creatinine of around 1 in a aged women will show a reduced GFR level as compared to the value of a male of age group around 25 yrs which will be considered as a normal GFR level.
The determination of GFR correctly can be a laborious task as it requires Intravenous infusions, radioactive compounds and esoteric laboratory measurements etc. Creatinine clearance is considered to be more practical method as it’s easy and requires one day urine sample and measuring the creatinine of serum and urine etc.
24-hour creatinine clearance is also helpful in determining more absolute results for GFR, for this accurate 24 hour urine collection is to be done and then urine & serum creatinine is measured.
Why the test is done?
Serum Creatinine test is done to check the following conditions.
- To determine the normal functioning of the Kidneys.
- To check how severe the Kidney disease is.
- To monitor the effect certain medications this can cause the Kidney damage/failure.
- To observe the condition of severe dehydration where the BUN levels are seen to rise more than the Creatinine levels in the body.
What are the preparations to be done for the test?
The doctor can ask the patient to stop the intake of certain medications which can alter the results of the test.
The drugs which can do the same are.
- Aminoglycosides like the Gentamicin
How it is done?
- Perform a venipuncture(Puncture of a vein, as for drawing blood) is done and the sample is collected in a tube around 3-4 ml
- The sample should be taken care of to prevent the condition of Hemolysis
- The sample should be send to lab for further investigation.
- The sample should be send to lab as soon as possible
- The site were the puncture was done should be pressed by applying pressure so that the bleeding stops from that site.
- The site should be monitored for a localized swelling filled with blood resulting from a break in a blood vessel and if its’ been sensed pressure should be applied on the same to stop the Hematoma.
- The medication which was stopped due to the test can be continued as the test is done.
What are the Risks attached with the test?
The risk attached with the drawing of the blood sample is little.
But certain other risks attached with it can be
- Infection or risk when the skin breaks during the sample collection
- The condition of Blood accumulation under the skin
- Felling loss of consciousness
- Excessive bleeding from the body of the person.
The Creatinine and Creatinine Clearance test measures the levels of the Creatinine in the blood and urine respectively to provide knowledge about the proper working of the Kidneys. The Creatinine Clearance value is found from the level of Creatinine in the Urine and blood and also from the Urine passed within 24 hours.
The normal values differ from lab to lab .But following range can still be considered normal.
In men, 0.8 to 1.2 mg/dl (
In women, 0.6 to 0.9 mg/dl
What are the Abnormal Results?
Higher levels of the Creatinine indicate:
Kidney damage around 50% or more than that due to certain disease of the Kidney.
- Indication of the condition of gigantism(abnormally large size.) and acromegaly( enlargement of the bones of the extremities, face, and jaw)
- Blockage of the urinary tract
- Heart failure
- Excessive blood loss which can lead to shock, gout other disease.
- Myasthenia gravis
High creatinine clearance
- Can be due to Vigorous exercise
- Injury to the muscle cells
- Carbon monoxide poisoning
High BUN-to-creatinine ratio:
- sudden (acute) kidney damage
- Blockage of the urinary tract like Kidney stone etc
- Bleeding of the digestive/respiratory tract
What does Lower level mean?
The reasons behind the Lower Serum Creatinine level can be due to following reasons:
- Loss of muscle mass due to certain disease such as muscular dystrophy (deterioration and wasting of muscle fibres,) or aging.
- Severe disease of Liver
- Intake of diet which has very poor protein content in it.
- It is seen that certain conditions such as Pregnancy the Creatinine levels do fall.
The reasons behind the Low creatinine clearance
Level can be due to following reasons:
- Serious /Fatal Damage of the Kidneys.
- Any severe fatal infection
- Cancerous growth
- Insufficient or low blood flow to the Kidneys.
- Urinary tract blockage.
- Presence of heart failure
- Dehydration or loss of fluids from the body.
- Cirrhosis of the Liver
The reasons behind Low BUN-to-creatinine ratio:
- Intake of diet poor in protein
- Severe injury to the cells of the muscles known as Rhabdomyolysis
- Pregnancy related conditions
- Cirrhosis of liver
- SIADH(A syndrome where the secretion of ant diuretic hormone is not proper)
What are the factors to be taken care of during the test?
Medications such as ascorbic acid, diuretics or barbiturates are seen to raise the levels of Creatinine in the blood.
- The athletes or sportsmen have massive muscle mass which is likely to increase the Creatinine levels despite the normal Kidney function.
- Phenolsulfonphthalein given prior to the test can raise the Creatinine levels if the Test is particularly done using the Jaffe’s reaction
During the metabolism process of muscle cells Creatinine is formed within tissue, or cell from Creatine and Creatinine phosphate and Creatinine gets removed into the urine from the plasma by the method of glomerular filtration without reasbsorption by the tubules.
The Renal tubular secretion is also one of the reasons behind the presence of small levels of Creatinine in the urine of a person So its seen that due to this the Creatinine Clearance overestimates the GFR rate more than 10% most of the times.
To determine the effective functioning of the Kidneys, it is important to access both the Creatinine levels and the renal Clearance of Creatinine. It is seen that the levels of blood creatinine don’t rise till sufficient damage has been done to the Kidneys.
People suffering from chronic kidney disease and those with risk factors attached to it such as diabetes, hypertension, cardiovascular disease, or hereditary kidney disease the estimation or prediction equation to estimate GFR from serum creatinine should be employed in such people.