A short duration renal acidification test

As earlier investigations of renal acidification capacity were poorly standardized it was considered important to develop a clinically useful method. The ability of the kidneys to acidify urine was studied in 19 normal persons by short ammonium chloride loading. Ammonium chloride was given in a dose of 150 mmol/m2 body surface in one of four different ways: whole tablets, crushed tablets, capsules and in solution. The degree of acidosis developed in each subject was measured in arterialized capillary blood samples. Urine was analysed for pH, titratable acid, ammonium ions (TA and NH4+) and phosphate. The excretion of TA, NH4+ and phosphate increased with the degree of acidosis in blood whilst urine pH decreased. The critical level appeared to lie around a base excess of -6 mmol/l below which all subjects could acidify their urine to a pH below 5.0. For clinical applications a frame of reference with tolerance limits is given for acidification capacity related to the degree of acidosis expressed as base excess.