Pseudohypophosphataemia as a result of bilirubin interference.

During the routine use of a discrete analyser it was noted that, when the serum bilirubin concentration was greater than 50 mumol/L, there was interference with serum phosphate determination measured by the formation of unreduced phosphomolybdate using a bichromatic system of measurement. The degree of interference was assessed by comparison with a reduced phosphomolybdate method (molybdenum blue). The interference cannot be removed by changing the secondary wavelength or by the use of a sample blank. It is proportional to the serum bilirubin concentration, but is not significant when this is less than 50 mumol/L. The monochromatic non-reduced phosphomolybdate method compares well with the reduced method.

Determination of reference intervals for serum magnesium.

Using a discrete analyzer and a dye-binding method, we measured magnesium in 800 patients' samples received for routine analysis. By excluding data from samples for which the calcium and (or) alkaline phosphatase values were outside defined reference limits, we established a reference interval for magnesium. Because the data showed a gaussian distribution, we could use parametric analysis to establish age-related intervals for both males and females.