Rehberg Test.
Rehberg test (creatinine clearance) is a laboratory test that evaluates kidney function by determining the glomerular filtration rate (GFR) based on clearance of endogenous creatinine. This method measures the volume of plasma the kidneys clear of creatinine per minute, reflecting the filtration capacity of the glomeruli.
Method principle:
- Creatinine is a product of muscle metabolism, normally completely filtered by the glomeruli without reabsorption or secretion in the tubules.
- The Rehberg test measures creatinine concentration in the blood and 24-hour urine, along with the total urine volume collected in 24 hours.
- GFR is calculated by the formula:
\( \text{GFR} = \frac{U_{cr} \times V}{C_{cr} \times T} \),
where \( U_{cr} \) is urine creatinine concentration, \( V \) is urine volume during collection time, \( C_{cr} \) is plasma creatinine concentration, and \( T \) is urine collection time in minutes.
- The result is normalized to a standard body surface area of 1.73 m², considering the patient’s height and weight.
Indications for the test:
- Assessment of kidney function when chronic kidney failure is suspected.
- Diagnosis and monitoring of kidney diseases including glomerulonephritis, pyelonephritis, and other nephropathies.
- Evaluation of kidney damage in systemic diseases (e.g., diabetes mellitus, hypertension).
- Monitoring the effectiveness of kidney disease treatments.
Normal values:
- GFR in adults is usually 90–140 ml/min/1.73 m².
- After age 40, GFR decreases by approximately 1% per year.
Features and limitations:
- A decrease in creatinine clearance indicates impaired kidney filtration function.
- Accuracy decreases in severe kidney failure and proteinuria.
- The test requires collection of 24-hour urine and blood samples, necessitating careful adherence to collection and preparation protocols.
Thus, the Rehberg test is an important and informative method for comprehensive assessment of kidney function and determination of glomerular filtration rate.