Renal handling of citrate in children with various kidney disorders.

Citrate (CIT) excretion was measured in 24 h urine of children with various kidney disorders and controls. It was normal in urinary tract infection, idiopathic urolithiasis, and idiopathic hypercalciuria in the absence of renal dysfunction, but reduced in acute glomerulonephritis, distal renal tubular acidosis, and chronic renal failure. Increased citraturia was observed in cystinosis and in idiopathic de Toni-Debré-Fanconi syndrome. Renal handling of CIT was studied in 45 children with various chronic kidney disorders under standard inulin clearance conditions. CIT clearance correlated well with GFR above 50 ml/min/1.73 m2. At lower levels, percent tubular reabsorption of CIT decreased rapidly, reaching levels between 17% and 41% at GFR less than 10 ml/min/1.73 m2; this disproportionate fall might be related to reduced renal CIT utilization at a relatively early stage of renal insufficiency. During acid loading tests, citraturia was lowered, with a decrease of both urinary pH and plasma bicarbonate in tubular disorders and in controls. The lowest CIT excretion was measured in incomplete renal tubular acidosis with magnesium wasting. The findings are discussed in view of recent physiological data on renal metabolism of CIT.