Serum Creatinine Test 53 By Fifth Stage Student Dr. Sakar Karem Abdulla M.Sc. Clinical Biochemistry

Creatinine Creatinine is a waste product that forms from breakdown of creatine, 95% of creatine occurring in skeletal muscle. Creatinine only have endogenous source and the amount of production depend on muscular mass.

Synthesis of creatine Creatine is synthesized in liver and kidney by two reactions: Transamidination of arginine and glycine to give ornithine and guanidinoacetic acid (GAA). Methylation of guanidinoacetic acid in presence of S-adenosylmethionine as methyl donor to give creatine and S-adenosyl homocysteine.

Synthesis of creatine

Fate of Creatine Creatine is reversibly phosphorylated to creatine phosphate by creatine kinase and stored in muscle as high energy phosphate. During muscle contraction the energy derived from ATP hydrolysis there after the ATP is regenerated by hydrolysis of creatine phosphate. Creatine and creatine phosphate spontaneously cyclize to form Creatinine and excreted in urine.

Fate of Creatine

Clinical significance of Creatinine Creatinine can be used to estimate muscle mass because the amount of Creatinine formation is proportional to the creatine phosphate content of the muscle. Serum Creatinine is a sensitive indicator of kidney disease so it may be ordered in patient with a suspected kidney disorder for diagnosis or periodically for monitoring of kidney disease .

Factors increasing serum Creatinine Decrease renal blood flow (shock, dehydration, Congestive heart failure) Renal dysfunction Post renal obstruction to urine

Factors decreasing serum Creatinine Decrease muscle mass (muscular dystrophy, paralysis) Pregnancy

Creatinine clearance Creatinine clearance: the volume of serum or plasma that would be cleared of creatinine in 1 mint. Creatinine clearance one of the most common methods used for estimating Glomerular filtration rate. Glomerular filtration rate (GFR): rate at which a waste product is cleared from the blood by the kidneys. Creatinine clearance is usually determined from measurement of creatinine in a 24-hour urine specimen and from a serum specimen obtained during the same collection period.

Creatinine clearance Normal value 88–128 mL/min in women 97–137 mL/min in men

Procedure for S. Creatinine Reagents Assay Standard Reagent A 500 µl Reagent B Mix and incubate for 5 minutes 100 µl serum First reading after 30 second( A1) 2nd reading after 90 second(A2) at 500 nm

Calculation S.Creatinine= ( A2-A1) Assay / (A2-A1) standard x conc.standard ( 2 mg/dl) Normal value female 0.5-1.1 mg/dl male 0.6-1.2 mg/dl Nephritis 2-4 mg/dl Renal failure 6 mg/dl