Biological variability and reference intervals for total plasma homocysteine

We compared plasma phosphate concentrations in general practice patients and hospital inpatients and outpatients over an 8-month period. The distribution of results in all three groups was similar and 12-16 % of results were at or below 0.8 mmol/L. In general practice patients, 8.3% of results from males and 12.1% from females were below the lower limit of their respective reference ranges. Eighteen of these patients (0.2% of results) had plasma phosphate concentrations <=0.4 mmol/L. On follow-up, only two of these patients had any attributable cause for their severe hypophosphataemia; in the remainder, it was unexpected and unexplained. Hypophosphataemia in outpatients and general practice patients is more common than has previously been appreciated. We present a strategy for further investigation of these patients.