ml/min), and P = plasma concentrationĬreatinine clearance should be corrected for body surface area. ![]() Creatinine clearance is then calculated using the equation:Ĭ = clearance, U = urinary concentration, V = urinary flow rate (volume/time i.e. The calculated clearance of creatinine is used to provide an indicator of GFR. This involves the collection of urine over a 24-hour period or preferably over an accurately timed period of 5 to 8 hours since 24-hour collections are notoriously unreliable. The most commonly used endogenous marker for the assessment of glomerular function is creatinine. The inconvenience associated with the use of exogenous markers, specifically that the testing has to be performed in specialized centers, and the difficulty to assay these substances, has encouraged the use of endogenous markers. The most promising exogenous marker is the non-radioactive contrast agent, iohexol, especially in children. Other exogenous markers used are radioisotopes such as chromium-51 ethylene-diamine-tetra-acetic acid (51 Cr-EDTA), and technetium-99-labeled diethylene-triamine-pentaacetate (99 Tc-DTPA). It involves the infusion of inulin and then the measurement of blood levels after a specified period to determine the rate of clearance of inulin. Assessment of GFR using inulin, a polysaccharide, is considered the reference method for the estimation of GFR. It should not undergo extrarenal elimination.Īs no such endogenous marker currently exists, exogenous markers of GFR are used. This article provides an update on the relevant biochemical tests for the assessment of renal function. Worldwide, the most common causes of CKD are hypertension and diabetes. According to the National Institutes of Health, the overall prevalence of chronic kidney disease (CKD) is approximately 14%. Tests of renal function have utility in identifying the presence of renal disease, monitoring the response of kidneys to treatment, and determining the progression of renal disease. Assessment of renal function is important in the management of patients with kidney disease or pathologies affecting renal function. The functional unit of the kidney is the nephron, which consists of the glomerulus, proximal and distal tubules, and collecting duct. We concluded that the normal range of BUN and Cr levels differed between young and elderly subjects, and that the decline in renal function correlated with age after the seventh decade.The kidneys play a vital role in the excretion of waste products and toxins such as urea, creatinine and uric acid, regulation of extracellular fluid volume, serum osmolality and electrolyte concentrations, as well as the production of hormones like erythropoietin and 1,25 dihydroxy vitamin D and renin. Although Cr levels did not correlate with age in elderly subjects, Cr levels divided by body surface area significantly correlated with age. Significant positive correlation was found between BUN levels and age in male elderly subjects. The mean Cr level in the elderly subjects was slightly higher than that in the control subjects. The mean BUN level in the elderly subjects was significantly higher than that in the control young subjects. The estimated normal range of BUN was 14-23 mg/dl both in male and female elderly subjects, and that of Cr was 0.9-1.3 mg/dl in male and was 0.7-1.1 mg/dl in female. We defined the normal range as range within the single SD-line of the remainder. We calculated the mean and the standard deviation (SD) in each group, and excluded subjects with values beyond twice the SD-line. This study was a part of the Kahoku Longitudinal Aging Study (KLAS) that aims to reveal the comprehensive functions in the aged. We measured the variables also in 315 cases of sex-matched young control subjects (male, 139 female, 176). ![]() To estimate normal ranges of blood urea nitrogen (BUN) and serum creatinine (Cr) levels in the aged, we measured BUN and Cr levels in 332 cases of apparent-healthy elderly subjects (male, 152 female, 180) aged 70 years or more.
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