Typically, GFR must be reduced by ~50 % before plasma urea or creatinine concentration rise above the upper limits of their respective reference range. it is only affected by change in GFR)īoth plasma urea and plasma creatinine concentration are imperfect indices of GFR neither analyte entirely fulfills the above criteria (see Table I below) and both lack sensitivity to detect minimal change in GFR.

Blood concentration of the substance must be unaffected by diet and/or change in the rate of endogenous.all that is filtered at the glomerulus appears in urine, and all that is in urine is due to glomerular filtration) It must be neither reabsorbed from the filtrate to blood nor secreted from blood to the filtrate by renal tubulecells (i.e.It must be freely filtered from blood at the glomerulus.It must be excreted only by the kidneys.kidney function) declines, urinary excretion of urea and creatinine also declines and blood concentration of both increases.įor the blood concentration of an endogenously produced substance to most accurately reflect GFR in health and disease, that substance must have the following properties: Irrespective of its cause, kidney disease is associated with decrease in GFR, and the severity of kidney disease correlates closely but inversely with GFR.Ī normal GFR (~125 mL/min) is presumptive evidence of healthy, functioning kidneys. The rationale for the use of creatinine or urea measurement to assess renal function is that plasma/serum levels of both reflect glomerular filtration rate (GFR), the parameter that defines kidney function for the clinician. Creatinine and urea blood levels reflect glomerular filtration rate (GFR)

Low bun creatinine ratio normal range