Kidney Function Tests PDF

Kurdistan Regional Government – Iraq Ministry of Higher Education & Scientific Research University of Duhok College of Health Sciences Department of Medical Laboratory Sciences Kidney Function Tests serum creatinine...

Kurdistan Regional Government – Iraq Ministry of Higher Education & Scientific Research University of Duhok College of Health Sciences Department of Medical Laboratory Sciences Kidney Function Tests serum creatinine Biochemistry Practical Lecture 2nd stage- 3rd semester Barhav Issa Abdullah BIOCHEMIST Metabolism: Interconversion of phosphocreatine and creatine is a particular feature of the metabolic processes of muscle contraction. Creatine and phosphocreatine are partially converted to a waste product called “Creatinine”. Thus the amount of creatinine produced each day is related to the muscle mass (and body weight), age, gender, diet, and exercise and does not greatly vary from day to day. In humans, half of stored creatine originates from food (like meat and fish), while the other half is synthesized mainly in the liver, pancreas and kidneys from three amino acids: arginine, glycine and methionine. 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 2  After synthesis, 95% of creatine is stored as phosphocreatine (or creatine phosphate) in skeletal muscles, while the rest is stored in the brain, heart and testis. Creatine phosphate is a high energy-yielding compound that supplies energy for muscle contraction. Creatinine is eliminated by glomerular filtration through the kidneys and excreted in urine without tubular reabsorption. 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 3 Clinical Significance: When there is kidney dysfunction, the ability of the kidneys to filter creatinine is diminished leading to a rise in serum creatinine. Therefore, serum creatinine level is used as an indicator of kidney function and is considered a better index than blood urea. The finding of an increased plasma creatinine indicates a fall in glomerular filtration rate (GFR). Value of Biochemical investigations in kidney disease: - Detecting the presence of renal disease. - Assessing the progress of the disease. But they are of less value in determining the cause of the disease 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 4 Increased plasma creatinine: is due to fall in glomerular filtration rate (GFR), the causes of decreased GFR include: 1. Any condition in which there is impaired renal perfusion (e.g., reduced blood pressure, fluid depletion, and renal artery stenosis). 2. Most diseases in which there is loss of functioning nephrons (e.g., acute glomerulonephritis, chronic glomerulonephritis). 3. Diseases in which pressure is increased on the tubular side of the nephron (e.g. urinary tract obstruction due to prostatic enlargement) 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 5 Decreased serum creatinine is of no significance and is seen in the following cases: Severe liver damage e.g. liver cirrhosis. Decreased muscle mass in the elderly. Small stature. Inadequate protein intake. Muscle wasting disease. 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 6 Laboratory measurement Specimen: Serum or plasma Principle of the test: Jaffe reaction: colorimetric reaction of creatinine with alkaline picrate to form a red-orange complex, the absorbance of which is measured kinetically at 490 nm and is directly proportional to creatinine concentration in the sample. 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 7  Reagents: R1: picric acid R2: Sodium hydroxide R3: Standard creatinine 2mg/dl. Manual Procedure: Test Tubes Blank Standard Test Working Reagent 1 ml 1 ml 1 ml (R1+R2) Demineralized water 100 µl Standard 100 µl Sample 100 µl Mix well. After 30 seconds, record absorbance A1 at 490 nm against reagent blank. Exactly 2 minutes after the first reading, record absorbance A2. 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 8  Calculation: A= absorbance Creatinine standard concentration = 2 mg/dl Expected values: In adults male 0.9 - 1.3 mg /dl female 0.6 -1.1 mg/dl 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 9  Creatinine Clearance 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 10 Creatinine clearance test: Clearance is defined as number of ml of a substance in blood cleared per minute. Creatinine clearance can be measured as an indicator of glomerular filtration rate (GFR). Creatinine clearance determination 1-by using 24h urine collection and serum creatinine: 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 11 2-by serum creatinine Expected values: Creatinine clearance (ml /min): Male 90-130 ml /min Female 80-120 ml /min 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 12  Limitations of Creatinine clearance equation: Th is calculation should not be used when serum [creatinine] is changing rapidly, when the diet is unusual (strict vegetarian diets, or creatine supplements), in extremes of muscle mass (malnutrition, muscle wasting, amputations) or in obesity. 11/5/2024 Barhav Issa Abdullah (BIOCHEMIST) 13