Reduced renal acid excretion in malnutrition: a result of phosphate depletion

Abstract

Eleven infants recovering from protein-calorie malnutrition secondary to acquired monosaccharide intolerance were found to have reduced plasma bicarbonate concentration associated with inadequate weight gain. Renal net acid excretion (NAE) was decreased to a mean of 34.2 µEq/1.73m²/min. Titratable acidity (TA) was markedly reduced, accounting for only 16% of NAE. This marked reduction in TA was associated with reduced mean phosphate (PO₄) excretion (.074 mg/min) and a reduced mean serum PO₄ (3.9 mg/dl), suggesting PO₄depletion. Two patients received intravenous phosphate loads, resulting in an increase in mean NAE from 35.1 to 89.7 µEq/1.73m²/min. A similar response was seen after oral PO₄ supplementation. Three patients were studied after partial correction of their acidosis. At a relatively low plasma bicarbonate concentration (mean = 16.6 mmoles/liter) significant amounts of bicarbonate were detected in the urine (mean = 8.7 µEq/1.73m²/min), suggesting a defect in bicarbonate reabsorption. Five patients studied after complete recovery from malnutrition had normal NAE in response to ammonium chloride load. The reduction in NAE appears to be secondary to unavailability of urinary buffers and a reduction in bicarbonate reabsorption; both of these defects can be explained by phosphate depletion.