Abnormal renal physiology Abnormal glomerular filtration rate An abnormally increased or reduced amount of fluid filtered out of plasma through glomerular capillary walls into Bowman's capsules per unit of time. HP:0012212 Abnormal GFR Glomerular filtration, the first step in urine formation, is the passive process of ultrafiltration of plasma from blood into Bowman's space as it traverses the glomerular capillaries. Because GFR varies by body size, it is indexed relative to an average body surface area (BSA) of 1.73 m2 and expressed as ml/min/per 1.73 m2. GFR cannot be measured directly; it can be assessed from clearance measurements or estimated from serum levels of endogenous filtration markers, such as creatinine or cystatin C. Clearance measurements require either multiple measurements of serum concentrations or timed urine collections and are not routinely performed. GFR is usually estimated from serum concentrations of a marker of filtration using GFR estimating equations. 2013-03-14T07:49:53Z UMLS:C0854050