INTRALABORATORY AND INTERLABORATORY QUALITY-CONTROL FOR ASSAY OF AMINO-ACIDS IN BIOLOGICAL-FLUIDS - 14 YEARS OF THE FRENCH EXPERIENCE

The functioning of an external quality-control scheme for amino acids set up in 1978 is described. Two measurements were made each month by participating laboratories on a control plasma sample provided by the quality-control center; freeze-dried samples were used from 1978 to 19 89 and liquid samples since 1990. In addition, two ''blind'' samples w ere sent to the laboratories each year. Every 3 months, the overall re sults and those of the individual laboratories were analyzed statistic ally. The validity of the liquid sample control is demonstrated. The p rogressive improvement of results is commendable. In 1990, the coeffic ients of variation for all participants ranged from 8.4% for alanine t o 23.5% for methionine. The standards used for calibration could contr ibute to the broad range of results, especially those for histidine an d ornithine. The use of blind samples made it possible to detect probl ems of calibration, of linearity of measurement, of contamination, and of identification of unusual amino acids.