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Chapter 045. Azotemia and Urinary Abnormalities (Part 2)

Assessment of Glomerular Filtration Rate Monitoring the GFR is important in both the hospital and outpatient settings, and several different methodologies are available (discussed below). In most acute clinical circumstances a measured GFR is not available, and the serum creatinine level is used to estimate the GFR in order to supply appropriate doses of renally excreted drugs and to follow short-term changes in GFR. Serum creatinine is the most widely used marker for GFR, and the GFR is related directly to the urine creatinine excretion and inversely to the serum creatinine (U Cr/PCr). The creatinine clearance is calculated from. | Chapter 045. Azotemia and Urinary Abnormalities Part 2 Assessment of Glomerular Filtration Rate Monitoring the GFR is important in both the hospital and outpatient settings and several different methodologies are available discussed below . In most acute clinical circumstances a measured GFR is not available and the serum creatinine level is used to estimate the GFR in order to supply appropriate doses of renally excreted drugs and to follow short-term changes in GFR. Serum creatinine is the most widely used marker for GFR and the GFR is related directly to the urine creatinine excretion and inversely to the serum creatinine UCr PCr . The creatinine clearance is calculated from these measurements for a defined time period usually 24 h and is expressed in mL min. Based upon this relationship and some important caveats discussed below the GFR will fall in roughly inverse proportion to the rise in PCr. Failure to account for GFR reductions in drug dosing can lead to significant morbidity and mortality from drug toxicities e.g. digoxin aminoglycosides . In the outpatient setting the serum creatinine is often used as a surrogate for GFR although much less accurate see below . In patients with chronic progressive renal disease there is an approximately linear relationship between 1 PCr and time. The slope of this line will remain constant for an individual patient and when values are obtained that do not fall on this line an investigation for a superimposed acute process e.g. volume depletion drug reaction should be initiated. It should be emphasized that the signs and symptoms of uremia will develop at significantly different levels of serum creatinine depending upon the patient size age and sex the underlying renal disease existence of concurrent diseases and true GFR. In general patients do not develop symptomatic uremia until renal insufficiency is usually quite severe GFR 15 mL min . A reduced GFR leads to retention of nitrogenous waste products azotemia such as .