Short Acidification Test and Its Interpretation with Respect to Age

O. Schück, MD, DS, Institute for Clinical and Experimental Medicine, PO Box 10, 14000 Prague – Krč (Czechoslovakia) Dear Sir, Agarwal and Cabebe [Nephron 26: 291, 1980] have shown in 16 persons in the age range of 29– 86 years that the capacity of the kidneys to excrete an acid load is diminished in elderly subjects. Reduced ammonium excretion and a small pH gradient defect could be demonstrated in old subjects. However, our knowledge pertaining to the influence of aging on this renal function is limited, and normal values of urine pH, titratable acidity (TA) and ammonium excretion in individual decades of healthy subjects achieved under conditions of the short acidification test are not available. We have studied this problem in 60 healthy volunteers in the age range of 18–70 years, using the short acidification test of Wrong and Davies. After 1-hour baseline urine collection ammonium chloride (0.1 g/kg body weight over a period of 30 min) was administered and subsequent by 5 1-hour periods were collected. We have tested the difference of urine pH, TA and ammonium excretion between the control period and the period in which the lowest urine pH was achieved. The results obtained are summarized in table I. From these data it is evident that the elderly individuals responded to acid loading by decreasing urine pH to the same level as young subjects did. TA excretion calculated per 100 ml Ccrbefore loading Table I. Average values ( ± SD) of urine pH, TA and ammonium excretion before (A) and after (B) acid loading (at the time of lowest urine pH) Age, years PH 3⁄8^·IOO μmol/min/100 Cc L1⁄8v.100 l_ cr μmol/min/100 Cc