A Young Woman with Recurrent Kidney Stones: Questions on Hypokalaemic Tubular Acidosis

Abstract

QUESTIONS @ POINT OF CARE range, 40-140 IU/L) and aspartate aminotransferase and bilirubin levels were normal. An arterial blood gas shows pH 7.36, PaCO 2 40 mmHg, PO 2 106 mmHg, and HCO 3 − : 21 mmol/L. The calculated plasma anion gap is: (140-(109 + 21) = 10 mmol/L. The intact parathyroid hormone and 25-hydroxyvitamin-D3 levels are within normal ranges. Serum calcium and serum phosphorus are 8.1 and 2.4 mg/dL, respectively. Urine volume is 1.5 L per 24 hours, pH 6.7 and 24-hour urine chemistries are calcium 2.9 mmol/day (d), phosphate 24 mmol/d, uric acid 5.5 mmol/d, oxalate 270 mmol/d, and citrate 0.6 mmol/d. Rheumatoid factor and antinuclear antibody are negative. Urine chemistry shows the following results: K + 31 mmol/L, Na + 100 mmol/L, Cl-105 mmol/L. The stones have been analysed biochemically and are composed of calcium phosphate (CaP)and calcium oxalate. On plain abdominal x-ray, calculi are seen in both kidneys (Fig. 1). In summary, this young woman suffers from recurrent nephrolithiasis and presents with a mild, hypokalaemic metabolic acidosis with normal anion gap, an inappropriately high urine pH and hypocitraturia. The aim of this contribution is to discuss the clinical approach to metabolic hypokalaemic tubular acidosis in a patient with recurrent nephrolithiasis. What is the significance of the plasma anion gap (PAG)? Addition of hydrogen ion (H+) can be detected by the appearance of new anions. These new anions may remain in the body, and/or be excreted in the urine or diarrhoea fluid. Acid