- This test is done on serum(clotted blood 3-5 ml) or plasma.
- The plasma may be prepared in fluoride or heparin.
- Flouride or heparin are not suitable for the enzymatic methods of creatinine.
- The sample is stable for 24 hours when kept at 4 °C.
- The non-fasting sample is acceptable.
- No preparation needed and the random sample can be taken.
- Lipemic and hemolyzed sample give a falsely high level.
- Heparin and fluoride are not good for the enzymatic procedure.
- Excessive exercise and high meat diet increase the level.
- Drugs may increase the level like gentamicin, cimetidine, chemotherapy (cisplatin),
Purpose of the test
- Creatinine level is done to assess kidney function.
- creatinine can be advised to see any effect of blood pressure or diabetes on the kidney.
- Creatinine is advised to monitor the renal diseases.
- Creatinine may be measured in amniotic fluid to assess the gestational (fetal) age and (fetal-maturity index), and cephalosporins.
- Creatinine is the end product of catabolism of creatine phosphate.
- Free creatinine is a waste product of creatine metabolism, is present in all body fluids and secretions.
- It is freely filtered by the glomerulus.
- There is diurnal variation when it is low at 7 AM and high at 7 PM.
- There is a slight increase after the meal and especially after the meat in the diet because a small amount is present in the meat.
- There is a very little effect by the liver function.
- Creatine phosphate is used in the contraction of skeletal muscles, by providing the energy.
- Creatinine is the waste product formed in the muscles from high energy compound creatine phosphate.
- The daily production of creatine and creatinine is dependent upon the muscle mass.
- The daily excreted creatinine is the function of muscle mass and is not dependent upon:
- Women excrete less creatinine than men because of less muscle mass.
- The daily excretion of the creatinine is relatively constant and is ±15% for a person per day.
- Creatinine excretion is not affected by protein metabolism or other external factors.
- So serum creatinine is the best measure of glomerular function (filtration).
- Creatinine is raised only when the 50% function of the kidney is lost.
- There is a minimal amount of creatinine in the urine from tubular secretion.
- Creatinine amount in the urine increases as the creatinine concentration rises in the blood.
- Creatinine is entirely excreted by the kidneys so directly proportional to the kidney function.
- Creatinine level remains normal with the normal excretory function of kidneys.
- Creatinine is excreted by the glomeruli as the filtrate and then it is not absorbed by the tubules.
- If there is any problem with glomerular filtration function then its level will increase in the blood.
- So renal disorders of kidneys give rise to increase in creatinine level like:
- Acute tubular necrosis.
- Urinary obstruction.
- This is more specific and sensitive parameter of the renal function and renal disease than blood urea nitrogen.
- This is specific for renal function and gives an idea about renal dysfunction.
- This is not a sensitive indicator of early renal disease.
- For 50% reduction in GFR, serum creatinine level will be double.
- BUN/creatinine ratio is important to evaluate the renal function.
- Normal in adult = 6 to 25
- Optimum level = 15.5
||0.6 to 1.2
|Newborn 1 to 4 day
||0.3 to 1.0
||0.2 to 0.4
||0.3 to 0.7
||0.5 to 1.0
|18 to 60 year
||0.9 to 1.3
||0.6 to 1.1
||1.0 to 1.7
||0.6 to 1.3
- To convert to SI unit x 88.4 = µmol/L
- Child = 0.3 to 0.7 mg/dl
- Adult = 0.5 to 1.0 mg/dl
- 18-60 years :
- male = 0.9 to 1.3 mg/d
- Female = 0.6 to 1.2 mg/dl
- Above 90 years
- Male =1.0 to 1.7 mg/dl
- Female = 0.6 to 1.3 mg/dl
Serum creatinine and creatinine clearance with the condition of the patient:
|Serum creatinine mg/dL
||Creatinine clearance mL/minute
|| The condition of the patient
|0.6 to 1.3
||100 ± 20
|1.4 to 2.4
||61 to 99
||still Seen in active person
|2.5 to 4.9
||24 to 60
||difficulty in performing the physical activity
|5.0 to 7.9
||12 to 23
||the patient cannot do daily activity
|8 to 12
||7 to 12
||acidosis and severe limitation of the activity
||6 or less
||patient in a coma and disorientated
Increased creatinine may be due to three causes:
- Pre-renal factors are:
- Congestive heart failure.
- Salt and water depletion due to:
- GIT fistulas.
- Increased use of diuretics.
- Uncontrolled diabetes mellitus.
- Diabetes insipidus.
- Excessive sweating (decreased salt intake).
- Renal factors are:
- Damage to:
- Interstitial tissue.
- Blood vessels.
- Post-renal factors are:
- Benign prostatic hyperplasia.
- Neoplasia compressing the ureter.
- Calculi obstructing the ureter.
- Congenital abnormalities obstructing or compressing the ureter.
The increased level is seen in:
- Renal function impairment both acute and chronic diseases.
- Postrenal obstruction of urine.
- Decrease in the blood perfusion because of any reason.
- Gigantism and Acromegaly.
- Injury to the muscles (Rhabdomyolysis).
- Myasthenia gravis.
- Muscular dystrophy.
- Dehydration due to loss of body fluids.
- May be seen in pregnancy during eclampsia and preeclampsia.
The decreased level is seen in:
- Decreased muscle mass.
- Pregnancy especially in a first and second trimester.
- Advanced and severe liver disease.
- inadequate dietary intake.
Drugs leading to an increased level of creatinine:
- Heavy metals chemotherapy e.g. Cisplatin.
- Nephrotoxic drugs like Cephalosporin e.g. Cefoxitin.
- Ascorbic acid can increase creatinine level.
- A diet high in protein like meat can increase the level.
The critical value is >4 mg/dL suggest severe renal disease.
Possible References Used
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