[Vitamin D3 overdosage due to rashly diagnosed rachitis in a child with distal tubular acidosis].

Metabolic acidoses are diseases causing many diagnostic and therapeutic problems. Compensated metabolic acidosis can be unrecognised for a long time. This refers especially to isolated renal tubular acidosis (RTA). Unrecognised RTA causes calcium and phosphorus balance disturbances with clinical signs of improper bone mineralization. It happens that some patients with mentioned problems are "treated" as rachitic and take high doses of vitamin D. As a result, serum calcium and phosphates as well as urine calcium increase, without the satisfied influence on bone mineralization. We present a case of a 3.5 months old baby, who was "treated" as ricket in vitamin D deficiency. This baby was "cured" with high doses of cholecalciferol (0.0875 mg/24h for 2 weeks, then 0.175 mg/24h for 3 weeks) because of craniotabes. This treatment was carried on without any metabolic tests and caused the following disturbances: 25(OH)D serum level - 102.7 ng/ml (normal 11-54), 1,25(OH)2D serum level - 39.5 pg/ml (normal 15-70), calcaemia 2.7-2.85 mmol/l, phosphataemia 2.1 mmol/l. In this time the considerable hipercalciuria (second morning urine sample Ca/cr ratio 2.06 mmol/mmol) occurred. The other laboratory test showed as follows: serum albumins 4.5 g/dl, alkaline phosphatase 188 U/l, acid phosphatase 10.7 U l, Cl- 114.9 mmol/l, Na 146 mmol/l, K 4.8 mmol/l, HCO3a 16.6-20.1 mmol/l and pCO2 3.63-3.85 kPa, serum anion gap 11 mEq/l; pH of morning urine 6.5-7. These results suggested the presence of distal RTA aside from symptoms of vitamin D overdosage. The high serum levels of calcium and phosphates, craniotabes, rather low serum alkaline phosphatase activity and presence of metabolic acidosis the symptoms after the normalisation of calcium and phosphorus balance suggested that the distal RTA had been prior to calcium disturbances.