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Many thanks for all the replies to my query two months ago regarding the 30 year old lady whose total calcium was 1.8 mmol/L and whose ionised calcium was discrepant with this at 1.52 mmol/L. She was presumed to have idiopathic hypoparathyroidism and was on Vit D treatment. Special thanks go to Dermot Neely who suggested that this girl may have hypocalcaemia with hypercalciuria due to a mutation in her calcium sensing receptor (NEJM 1996; 335: 1115-22. Certainly, her biochemical presentation fits this condition exactly (although there is no mention of any total/ionised discrepancy). Genetic analysis is on its way to London. Interestingly, the authors of the NEJM paper could not explain the underlying mechanism responsible for the hypercalciuria and nephrocalcinosis that occurs in these patients with vitamin D therapy when their total calcium would suggest they are hypocalcaemic. Perhaps this discrepancy between total/ionised calcium is responsible, especially since we now know her mother, who is not on treatment, also has a total calcium of 1.8 mmol/L but a more consistent ionised calcium of 0.9 mmol/L. Needless to say this requires further investigation. Dr. Eric S. Kilpatrick Consultant in Chemical Pathology Department of Clinical Biochemistry Hull Royal Infirmary Anlaby Road Hull HU3 2JZ Tel 01482-674312 Fax 01482-674310 ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%