Biochemistry - Determination of Serum Creatinine PDF

Almaaqal University Biochemistry Determination of Serum Creatinine Dr/ Wael Sobhy Darwish Biochemistry PhD  Overview Creatine is synthesized in the liver, pancreas, and kidneys fro...

Almaaqal University Biochemistry Determination of Serum Creatinine Dr/ Wael Sobhy Darwish Biochemistry PhD  Overview Creatine is synthesized in the liver, pancreas, and kidneys from the amino acids arginine, glycine, and methionine. Creatine is transported through the circulatory system to muscle where it is converted to phosphocreatine and acts as an energy reservoir much like ATP. Creatinine is a waste product produced in your muscles from the breakdown of creatine (Creatinine is formed by the hydrolysis of creatine).  Almost all creatinine is excreted by the kidneys, so blood levels are a good measure of how well your kidneys are working.  Why it is done? Determine whether the kidneys are functioning normally. Serum creatinine is a more specific and sensitive indicator of renal disease than BUN why? Production of creatinine depends on an individual's muscle mass, which usually fluctuates very little with normal kidney function, then, the amount of creatinine in the blood remains relatively constant and normal. For this reason, and because creatinine is affected very little by liver function, an elevated blood creatinine is a more sensitive indication of impaired kidney function than the BUN  Disadvantage of creatinine Unfortunately, serum creatinine is very insensitive to even substantial declines in glomerular filtration rate. Glomerular filtration rate may be reduced by up to 50% before serum creatinine becomes elevated.  Sample Serum or plasma, Urine The only acceptable anticoagulants are heparin and EDTA Stability in serum: Creatinine in serum is stable for twenty-four (24) hours at refrigerated temperatures (2 - 8°C) and several months when frozen (-20° C). Spot urine or 24-hour urine sample collection is needed for the measurement of urine creatinine.  ASSAY PRINCIPLE In 1886 Jaffé described a method for the measurement of creatinine in biological fluids. This method involved precipitation of protein. Although several methods have been described since then, the original Jaffé technique is still the most widely used today. Creatinine in alkaline solution forms a yellow-red complex with alkaline picrate.  PROCEDURE 1. Assay conditions: Wavelength: 480-520 nm Cuvette: 1 cm light path Temperature: 20-25ºC  PROCEDURE Blank Standard Sample WR(mL) 1.0 1.0 1.0 Standard (µL) -- 100 -- Sample (µL) -- -- 100 Mix, after 30 sec. read initial absorbance (A1). After exactly 2 min. later, read absorbance (A2).  Normal range: Male: 0.6–1.4 mg/dl Female: 0.6–1.2 mg/dl Note: The quantity produced depends on the size of the person and their muscle mass. For this reason, creatinine concentrations will be slightly higher in men than in women and children.  Creatinine levels higher than normal levels may be due to Prerenal causes Caused by a decrease in cardiac output, resulting in inadequate blood supply to the kidneys as in heart disease, dehydration, excessive blood loss that causes shock. Caused by Muscle disease such as acromegaly Renal causes Impaired kidney function; 50% loss of renal function is needed to increase serum creatinine from 1.0 to 2.0 mg/dL; therefore the test is not sensitive for mild to moderate renal injury. Creatinine levels increase more slowly than blood urea nitrogen (BUN) levels, so an increase in creatinine usually indicates chronic kidney problems.  Some factors that can lead to higher creatinine levels Eating large amounts of cooked meats Taking creatine supplements Recent high intensity exercise High muscle mass (very muscular body frame, bodybuilder) Taking medications such as cimetidine, fenofibrate, or trimethoprim  Low levels of creatinine Low levels of creatinine are not common and are not usually a cause for concern. Low blood creatinine levels can indicate: A diet very low in protein. A decrease in muscle mass caused by a disease, such as muscular dystrophy. Myasthenia gravis Pregnancy can also cause low blood creatinine levels