СКФ (скорость клубочковой фильтрации) eGFR, CKD-EPI

Creatinine clearance (Rehberg test; creatinine clearance test) estimates glomerular filtration by comparing creatinine concentration in serum with that excreted in a timed urine collection. The test is used to assess overall kidney function, approximate the glomerular filtration rate (GFR), and assist with staging and monitoring chronic kidney disease. It supports clinical decision-making when nephrotoxic medications are prescribed and in settings where volume depletion may depress filtration, such as severe dehydration. Measured creatinine clearance is particularly useful when a direct clearance value is needed; however, in routine practice, estimated GFR derived from serum creatinine is often used for convenience.

The kidneys filter circulating plasma through millions of glomeruli; most filtrate is reabsorbed, while solutes not reclaimed are eliminated in urine. Creatinine is generated at a relatively steady rate from creatine phosphate in muscle, is freely filtered, undergoes minimal tubular reabsorption, and a small fraction is secreted by the tubules. As filtration falls, serum creatinine rises. By measuring creatinine in a timed (often 24‑hour) urine collection together with a concurrent serum value, creatinine clearance can be calculated to approximate the glomerular filtration rate. In healthy young adults, clearance is roughly 125 mL/min, reflecting the aggregate filtration of all functioning nephrons. When kidney function is substantially reduced, the proportional contribution of tubular secretion increases, causing measured creatinine clearance to overestimate true GFR, particularly in advanced renal failure. Although clearance can be measured directly with urine collection, serum‑based equations that estimate GFR are frequently used in practice because they are simpler for patients and clinics. A reduced GFR warrants evaluation for underlying etiology. Chronic kidney disease is most commonly driven by hypertension and diabetes mellitus; if those are absent, additional diagnostic workup is indicated. Serial creatinine clearance (or serial eGFR) enables tracking of renal function over time and supports adjustment of drug therapy. Factors that suppress tubular creatinine secretion—such as cimetidine, trimethoprim, and ketoacids—can lower measured clearance and diminish the accuracy of GFR estimation, with the effect most evident in severe renal impairment.