Chemical pathology case conference - Renal function tests

Abstract

Glomerular filtration rate (GFR) is the best index for assessing the overall renal function but it can only be determined indirectly. Measurement of serum creatinine is the simplest and the most widely used method for GFR assessment. Correct interpretation of serum creatinine levels requires knowledge about the age, sex, muscle mass and physiological states of individual patients and factors that may interfere with laboratory measurements. Determination of creatinine clearance (CrCl) using 24-hour urine sample is also used for GFR assessment. CrCl can overestimate GFR because of the renal tubular secretion of creatinine. Under or over collection of 24-hour urine can cause significant errors in CrCl calculations. The Cockcroft & Gault formula and the abbreviated MDRD equation can provide additional information to serum creatinine level alone. Understanding their limitations is required for accurate application of these equations in clinical practice. Numerous disease processes and pharmaceutical agents have primary and secondary effects on the kidneys. A stepwise investigative approach is required to delineate the underlying cause of renal impairment. Physical examination, routine laboratory tests and some basic radiological examinations help divide the cause of renal impairment into prerenal, renal and postrenal forms. This information is very useful in guiding appropriate management and further investigations.