Lipschitz D A, Skikne B A, Thompson C
Am J Clin Nutr. 1981 May;34(5):951-6. doi: 10.1093/ajcn/34.5.951.
For the epidemiological evaluation of iron stores the precision of serum ferritin measurement in the low range are important for the accurate determination of the prevalence of iron deficiency and the detection of subtle changes in serum ferritin levels after food iron manipulation. In addition the recognition of iron overload and the evaluation of its severity are important. In this study samples with low serum ferritin values were repetitively measured in a classic radioimmunoassay (RIA) and in two "2-site" immunoradiometric assays (IRMA), one of which used a polystyrene bead and the other a polystyrene tube fas the solid phase. Variability was significantly less with the IRMA using a bead than that using a tube. Optimum precision was noted when samples were run at the lowest possible dilution (1:10) with relatively long reaction times. The bead IRMA was also more precise that the RIA which had a standard curve with 50% radioactive binding (maximum precision) of 40 ng/ml. Within the normal serum ferritin range (12 to 300 ng/ml) extremely similar results were obtained with an RIA and IRMA. However, when iron overload samples (serum ferritin values greater than 2000 ng/ml) were examined the RIA gave values significantly lower than those obtained by IRMA. The lower values by RIA may be related to the immunological heterogeneity of serum ferritin which is maximized by an assay performed in antigen excess (RIA) and minimized by one performed in antibody excess (IRMA). These observations indicate a need for the development of specific serum ferritin assays for epidemiological studies. By manipulating the components of the standard curve the RIA and IRMA can be optimized to provide maximum precision when low serum ferritin values are being measured. in choosing an assay the ability of the method to determine the severity of iron overload must also be taken into consideration.
对于铁储备的流行病学评估而言，低浓度范围内血清铁蛋白测量的精密度对于准确确定缺铁患病率以及检测食物铁摄入调整后血清铁蛋白水平的细微变化至关重要。此外，识别铁过载及其严重程度的评估也很重要。在本研究中，对血清铁蛋白值较低的样本分别采用经典放射免疫分析法（RIA）以及两种“双位点”免疫放射分析法（IRMA）进行重复测量，其中一种IRMA采用聚苯乙烯珠作为固相，另一种采用聚苯乙烯管作为固相。采用珠的IRMA的变异性显著低于采用管的IRMA。当样本以尽可能低的稀释度（1:10）运行且反应时间相对较长时，可获得最佳精密度。珠IRMA也比RIA更精确，RIA的标准曲线在50%放射性结合（最大精密度）时为40 ng/ml。在正常血清铁蛋白范围内（12至300 ng/ml），RIA和IRMA获得的结果极为相似。然而，当检测铁过载样本（血清铁蛋白值大于2000 ng/ml）时，RIA给出的值显著低于IRMA获得的值。RIA得出较低值可能与血清铁蛋白的免疫异质性有关，在抗原过量（RIA）的检测中这种异质性被最大化，而在抗体过量（IRMA）的检测中被最小化。这些观察结果表明，需要开发用于流行病学研究的特异性血清铁蛋白检测方法。通过调整标准曲线的成分，在测量低血清铁蛋白值时，可对RIA和IRMA进行优化以提供最大精密度。在选择检测方法时，还必须考虑该方法确定铁过载严重程度的能力。
