Renal function tests glomerular filtration rate

Histopathological evidence of renal damage has been observed in lead-exposed workers. Renal ultrastructure and function were examined in five men with heavy occupational exposure to lead (Cramer et al. 1974). In addition, renal function was evaluated in two men from whom renal biopsies were not obtained. PbB levels ranged from 71 to 138 pg/dL. Renal function tests were normal in all except for a reduced glomerular filtration rate in one worker. Two subjects with relatively short exposure to lead (6 weeks and 8 months) and PbB levels of 89-129 pg/dL had intranuclear inclusions in the proximal tubules. Renal biopsies from workers with longer periods of lead exposure (4-20 years, PbB levels of 71-138 pg/dL) had diffuse interstitial or peritubular fibrosis. Glomeruli were normal in all subjects. 

Inulin is used in an important test for renal failure called the inulin clearance method (Gretz et al., 1993 Chiu, 1994). As inulin is neither secreted nor reabsorbed in the kidney, it can be administered by injection to measure glomerular filtration rate. The relative amounts of inulin in the plasma and urine give an indication of renal function. 

As renal function improves, the excretion of urea increases and the concentration of urea in blood declines. So a reduction in blood urea nitrogen (BUN) is also a useful sign of returning kidney function. More complex tests, such as creatinine clearance, would be needed to check whether the glomerular filtration rate (GFR) has returned to normal. 

Renal function is an indication of the physiological state of the kidney glomerular filtration rate (GFR) describes the flow rate of Altered fluid through the kidney, while creatinine clearance rate (Ccr) is the volume of blood plasma that is cleared of creatinine per unit time, and is a useful measure for approximating the GFR. Most clinical tests use the plasma concentrations of the waste substances of creatinine and urea, as well as electrolytes, to determine renal function. The nephron is the functional unit of the kidney (Figure 10.1) it consists of two parts ... 

Creatinine has no useful function and is eliminated by renal glomerular filtration and to a small extent by renal tubular secretion. Creatinine clearance approximately parallels the glomerular filtration rate (GFR) and is used as a kidney function test. It is calculated as follows ... 

Although the EDTA test has been shown to be safe even in the presence of renal failure [77], the cumulative nephrotoxicity of prolonged EDTA therapy in patients with markedly reduced glomerular filtration rates is unknown. Reports that CaNa2EDTA therapy has been followed by deterioration of renal function warrant careful follow-up of treated patients [78]. Despite these caveats, it may be appropriate to perform EDTA lead-mobilization tests in individuals with gout or hypertension and renal failure or interstitial nephritis of unknown etiology since a positive test may provide the best available indication of etiology. 

Early kidney disease is difficult to detect. The urinalysis is normal in early lead nephropathy and the blood urea nitrogen and serum creatinine increase only when two-thirds of kidney function is lost. Measurement of creatinine clearance can often detect earlier disease as can other methods of measurement of glomerular filtration rate. An abnormal Ca-EDTA mobilization test has been used to differentiate between lead-induced and other nephropathies, but this procedure is not widely accepted. A form of Fanconi syndrome with aminoaciduria, glycosuria, and hyperphosphaturia indicating severe injury to the proximal renal tubules is occasionally seen in children. 

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