A recently developed, simple and sensitive radioimmunoassay has been used to examine 24 h excretion and plasma levels of Tamm-Horsfall glycoprotein (THG) in normal subjects, stone formers and patients with stable chronic renal disease. In normal subjects THG excretion ranged from 22 to 66 mg/24 h, with no sex difference and no correlation with creatinine clearance or body surface area. There was no correlation between 24 h THG excretion and urine volume, pH or osmolality, excretion of Na+, K+ or Ca2+ or free-water clearance. There was a small significant correlation between plasma THG concentration and urinary THG excretion. A good correlation was obtained between the THG/creatinine ratio in 24 h and random samples. This made possible the use of random samples to establish a reference range for THG excretion of 0.15-0.50 micrograms/ml of creatinine clearance which did not depend on sex or age. The excretion rate of THG in stone formers was generally within the reference range. It was not significantly different in those who were hypercalciuric or in those taking thiazides. In patients with chronic renal disease there was a good correlation between 24 h THG excretion, plasma THG concentration and creatinine clearance. The range of excretion of THG per ml of creatinine clearance was greater than in normal subjects, independent of the type of renal disease and unrelated to proteinuria. In patients with glomerulonephritis the excretion of THG per ml of creatinine clearance was significantly higher in those with well-preserved tubules compared with those with tubular atrophy.

A rapid, specific radioimmunoassay has been used to measure Tamm-Horsfall glycoprotein (TH glycoprotein) in urine. The apparent concentration increased with increasing dilution of urine in water, reaching a plateau at 1 in 20. This increase was greater the higher the osmolality and TH glycoprotein concentration and the lower the pH of the original sample. A dilution of 1 in 100 was chosen for routine assay. Whole urine was centrifuged and the dissolved precipitate and supernatant assayed to quantify the proportion of TH glycoprotein of TH glycoprotein initially present in highly aggregated form. This correlated positively and significantly with increasing osmolality, decreasing pH and increasing TH glycoprotein concentration. When the urine was diluted 1 in 100 in water, no TH glycoprotein was precipitated by centrifugation and the measured concentrations were unaffected by alterations of urine pH or calcium concentration or by addition of sodium dodecyl sulphate. Parallelism was demonstrated between the diluted samples and the disaggregated standard preparation. Recovery of added standard to diluted urine varied between 96 and 114%. The apparent concentration of TH glycoprotein in neat or diluted urine was not affected by freezing or by storage at 4 degrees C or room temperature for at least 2 days. A physiological range for the urinary excretion rate was established as 22--56 mg/24 h, based on samples from 29 individuals with normal renal function, as defined by their creatinine clearance. There was no significant correlation between serum concentrations of TH glycoprotein and its urinary excretion rate, nor between urinary excretion rate and creatinine clearance.

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