1ST MORNING URINE PH IN THE DIAGNOSIS OF RENAL TUBULAR-ACIDOSIS WITH NEPHROLITHIASIS

Few reports of patients with renal stones compare fasting first mornin g urine pH with the lowest urine pH after a single oral dose of 0.1 g/ kg ammonium chloride. We studied these values in 110 individuals, incl uding 96 stone formers and 14 non-stone forming controls. We hypothesi zed that fasting first morning urine pH greater-than-or-equal-to 6. 1 0 is abnormal. Nine of ten patients who had urine pH greater-than-or-e qual-to 5.25 after NH4Cl, had pH greater-than-or-equal-to 6.10 for bot h a single and a second first morning urine, giving a sensitivity of 9 0%. In contrast, a single fasting first morning urine pH greater-than- or-equal-to 6.10 was found in 19 of 100 individuals with pH <5.25 afte r ammonium chloride. However, only 4 of these 100 individuals had abno rmal fasting first morning pH greater-than-or-equal-to 6.10 on two occ asions, giving a specificity of 96% for the two urines. Useful predict ion of urine pH greater-than-or-equal-to 5.25 after ammonium chloride occurs when two fasting first morning urines have pH greater-than-or-e qual-to 6.10.