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Does anyone have a paediatric protocol for a bicarbonate load test? We are investigating a 4 year old who has an x-ray diagnosis of osteopetrosis. The diagnosis which was made following a routine X-ray of a fracture. The child is deaf but has none of the haematological hallmarks of the lethal variant. Our routine investigations revealed a suggestion of renal tubular acidosis which may indicate that this patient is suffering from the milder form of osteopetrosis associated with carbonic anhydrase deficiency: Serum bicarbonate(venous) 21.6 mmol/L (22 - 30) Venous pH 7.354 serum lactate 1.8 mmol/L (0.63 - 2.4) Serum chloride 104 mmol/L (96 - 109) Urine pH 7.17 Overnight culture of urine no significant growth (This urine specimen was taken a week after the blood, unfortunately, due to the difficulties encountered during phlebotomy The text books suggest that a bicarbonate load test should help. I understand the theory, but can anyone help with a protocol for the bicarbonate load test which is practical in an uncooperative 4 year old? I think that it is possible to measure red cell carbonic anhydrase isoenzymes but nobody in the UK is listed as offering the service. -- Robert Hill %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%