Creatinine clearance

DESCRIPTION:
Renal clearance is a measure of the functional capacity of the kidneys. The term clearance refers to the number of milliliters of plasma that is “cleaned” of a substance in 1 second. To test the functional ability of the kidneys using clearance, substances are used that meet the following conditions: they must be freely filtered through the glomerulus, they must not be bound to plasma proteins, and the plasma concentration and distribution of the substance must be constant.

Substances that are only filtered through the glomeruli and are neither reabsorbed nor excreted in the tubules are used to test glomerular function (eg inulin, mannitol, creatinine). Endogenous creatinine clearance is most often determined to test glomerular kidney function. Creatinine is filtered through the glomeruli, very little is reabsorbed in the tubules and some is secreted in the tubules. Endogenous creatinine clearance with minor deviations corresponds to glomerular filtration. Creatinine clearance values are slightly higher than glomerular filtration and this is due to the fact that some excretion of creatinine occurs in the tubules.

DETERMINATION:
Creatinine concentration is determined photometrically by the Jaffe method using picric acid. The sample for analysis is serum, plasma (EDTA or heparin) and urine (24 hours). Serum/plasma stability: 20°C to 25°C is 7 days, 2°C-8°C is 7 days, -20°C is one month. Urine stability: 20°C-25°C is two days, 2°C-8°C is 6 days, -20°C is six months.

CLINICAL SIGNIFICANCE:
Determination of creatinine value in serum and urine is an important diagnostic data for the assessment of renal function. However, the determination of serum creatinine concentration alone is not always reliable enough, because even people with normal creatinine values can have kidney damage and reduced glomerular filtration. In the early stages of kidney damage, relatively small changes in serum creatinine concentration are associated with large changes in glomerular filtration. 1) Physiological changes

When evaluating the results of creatinine clearance, the dependence of age and glomerular filtration should be taken into account. For adults, the following formula applies: Glomerular filtration (ml /min) = 157 – (1.16 x age expressed in years) or Glomerular filtration (ml /s) = 2.61 – (0.019 x age expressed in years) 2) Pathological changes A) Increased values of creatinine clearance in: Acromegaly / Burn B) Decreased values of creatinine clearance in: Acute and chronic pyelonephritis / Anorexia nervosa / Liver cirrhosis / Extrahepatic biliary obstruction / Renal artery embolism / Gout / Glomerulonephritis / Growth hormone deficiency / Hepatolenticular degeneration / Hyperparathyroidism / Congestive heart failure / Medullary cystic disease / Multiple myeloma / Polycystic kidney disease / Pre-eclampsia / Renal vascular hypertension / SLE

RISK FACTORS:
Reduced values:
– Dehydration – Age – Physical exertion (severe) – Starvation – Nephrectomy – Lead poisoning – Vegetarianism
Increased values:
– Diet rich in proteins – Daily rhythm – Physical effort – Menstrual cycle – Obesity – Pregnancy

EFFECT OF DRUGS:
Reduced values:
cephalothin, cefoxitin
Increased values:
cefoxitin, levodopa

RESULT:
The reference interval depends on gender, age and work method. The reference interval is displayed with each validated result.