Abstract

Reference change values (RCVs) are used by the physician to judge whether a change in analyte concentration from one sample to the next may represent a clinically significant change. Published RCVs are usually given as fixed percentages of the analyte concentration in the first sample. The accuracy of published RCVs is not well known. We obtained public-use data from the US National Health and Nutrition Examination Survey (NHANES) 2001–2002 to study the distribution of changes in the concentration of eight commonly used analytes. Specimens were obtained on two occasions 7–47 days apart from 279 to 411 individuals with an analyte concentration within the reference interval in both samples. The analytes were albumin, calcium, cholesterol, phosphate, potassium, sodium, hemoglobin and thrombocytes. For each analyte, normal within-subject biological coefficient of variation from the EFLM Working Group on Biological Variation and the NHANES analytical coefficient of variation were used to calculate the 5 and 95 percentile RCVs. These RCVs were calculated as fixed percentages of the analyte concentrations in the first sample and compared to the empirical 5 and 95 percentiles. The sensitivity of the RCVs in detecting changes outside the empirical percentiles ranged from 0.35 for sodium to 0.80 for albumin. The specificity of the RCVs in detecting changes inside the empirical percentiles ranged from 0.85 for potassium to 0.97 for thrombocytes. Calculating RCVs as fixed percentages of the analyte concentration in the first sample lessened the diagnostic accuracy. RCVs given as a function of the first result would perform better.

摘要

医生使用参考变化值 (RCV) 来判断分析物浓度从一个样品到下一个样品的变化是否代表临床上显着的变化。公布的 RCV 通常以第一个样品中分析物浓度的固定百分比给出。已发布的 RCV 的准确性尚不清楚。我们从 2001-2002 年美国国家健康和营养调查 (NHANES) 中获得了公共使用数据，以研究八种常用分析物浓度变化的分布。除了 279 到 411 个人之外，两个样本中的分析物浓度都在参考区间内，在 7-47 天内两次获得了样本。分析物是白蛋白、钙、胆固醇、磷酸盐、钾、钠、血红蛋白和血小板。对于每种分析物，来自 EFLM 生物变异工作组的正常受试者内生物变异系数和 NHANES 分析变异系数用于计算 5 和 95 百分位 RCV。这些 RCV 计算为第一个样品中分析物浓度的固定百分比，并与经验 5 和 95 百分位数进行比较。RCV 检测经验百分位数以外变化的灵敏度范围从钠的 0.35 到白蛋白的 0.80。RCV 在检测经验百分位数内变化的特异性范围从钾的 0.85 到血小板的 0.97。将 RCV 计算为第一个样品中分析物浓度的固定百分比会降低诊断准确性。作为第一个结果的函数给出的 RCV 会表现得更好。