Proximal RTA in CAII deficiency with osteopetrosis is less common than distal RTA (I think), and given that the child is not particularly acidotic it might be worth considering a form of ammonium chloride loading test in the first instance. If fractional bicarbonate excretion was normal this might not exclude CAII deficiency. The urine pH would be more significant if it was a first void morning urine. Even then I'm not sure you need to do a bicarbonate load: what you want to know is the fractional excretion of HCO-3 during NaHCO3 loading, OR at a time when the plasma HCO-3 is normal. I think I would probably just measure fractional bicarbonate excretion in the first instance without necessarily loading. The plasma bicarbonate is only minimally lower than you would want to achieve with a loading test in any case, and if the bicarbonate is pouring out into the urine, the loading test would not be of additional value. Any other thoughts? Aubrey Blumsohn Dundee At 22:20 30/03/99 +0100, you wrote: >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 > > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%