Møller J, Rasmussen K, Christensen L
Aarhus University Hospital at Skejby, Department of Clinical Biochemistry, DK-8200 Aarhus N, Denmark.
Clin Chem. 1999 Sep;45(9):1536-42.
The use of analyses for methylmalonic acid (MMA) and total homocysteine (HCY) in plasma has become widespread. Realizing the need for external quality assessment for these measurements, we started a program in 1997. The results for 1998 are reviewed in this report.
Fourteen laboratories participated with 15 sets of results for MMA, and 28 laboratories participated with 34 sets of results for HCY. Results for four identical samples, made up from the same unmodified serum (MMA) or EDTA-plasma (HCY) pool, sent out under different identifications, were used for assessing the imprecision. Samples made up from the same pools supplemented with MMA or L-HCY to three concentrations were used for assessing the recovery. By using literature data for the biological variation, quality goals for both analytes were calculated.
The overall within-laboratory CV was 12% for MMA and 7.5% for HCY. Gas chromatography-mass spectrometric HCY results had lower imprecision than the HPLC or immunoassay results. For MMA, no significant between-laboratory component of variance was found. Only results for HCY obtained with HPLC methods showed significant between-laboratory variance.
Eight of the 15 participants achieved the minimum imprecision goal for MMA vs 9 of the 34 participants for HCY. The minimum quality goals for bias as approximated by the recovery were achieved by 13 participants for MMA and 26 for HCY.
血浆中甲基丙二酸（MMA）和总同型半胱氨酸（HCY）分析的应用已十分广泛。鉴于认识到对这些检测进行外部质量评估的必要性，我们于1997年启动了一项计划。本报告回顾了1998年的结果。
14个实验室参与了MMA的检测，提供了15组结果；28个实验室参与了HCY的检测，提供了34组结果。由同一未改性血清（MMA）或EDTA血浆（HCY）混合液制成的四个相同样本，以不同标识分发，用于评估不精密度。由同一混合液补充MMA或L-HCY至三种浓度制成的样本用于评估回收率。利用生物学变异的文献数据，计算了两种分析物的质量目标。
MMA的总体批内变异系数为12%，HCY为7.5%。气相色谱-质谱法检测HCY的结果不精密度低于高效液相色谱法或免疫分析法的结果。对于MMA，未发现显著的实验室间方差成分。仅高效液相色谱法检测HCY的结果显示出显著的实验室间方差。
15名参与MMA检测的人员中有8人达到了MMA的最低不精密度目标，而34名参与HCY检测的人员中有9人达到了该目标。以回收率近似的偏差最低质量目标，MMA有13名参与者达到，HCY有26名参与者达到。
