Leslie W D, Dupont J O, Peterdy A E
The University of Manitoba, Winnipeg, Canada.
J Nucl Med. 1999 Mar;40(3):422-8.
Measurement of red cell mass with isotope dilution remains an important diagnostic test in the evaluation of patients with suspected polycythemia vera (PCV). Results and reference ranges are typically expressed in units normalized for body weight (mL/kg). Obesity is common in polycythemic patients, and it is important to know how the various published normative ranges compare across a wide range of body weights.
We retrospectively reviewed 51 consecutive patients referred for red cell mass determination with 51Cr red blood cell dilution. Results were expressed in milliliters per kilogram (mL/kg) by using the actual patient weight and after adiposity adjustments using ideal body weight, body mass index (BMI) and combinations of height-weight, including body surface area. Results were classified as normal, elevated or PCV.
There was a high prevalence of obesity in our population (28/51 [55%] with BMI > 27 kg/m2, BMI range 16.0-54.8 kg/m2). The method used to compensate for obesity had a dramatic effect on the derived red cell mass, the fraction of patients with elevated measurements and the fraction of patients meeting criteria for PCV. Concordance for categorization as normal, elevated or PCV by all methods was only 47.1%.
Obesity is a common confounding factor in the interpretation of red cell mass measurements. Currently published reference ranges generate inconsistent results when extrapolated to obese patients. Further normative data on obese subjects are needed to determine which method (if any) is optimal.
采用同位素稀释法测量红细胞容量仍然是评估疑似真性红细胞增多症（PCV）患者的一项重要诊断测试。结果和参考范围通常以按体重标准化的单位（毫升/千克）表示。肥胖在红细胞增多症患者中很常见，了解各种已发表的正常范围在广泛体重范围内的比较情况很重要。
我们回顾性分析了51例连续接受51Cr红细胞稀释法测定红细胞容量的患者。结果以每千克毫升数（mL/kg）表示，分别采用患者实际体重以及使用理想体重、体重指数（BMI）和身高体重组合（包括体表面积）进行肥胖调整后的数据。结果分为正常、升高或PCV。
我们研究人群中肥胖的患病率很高（28/51 [55%] 的BMI > 27 kg/m2，BMI范围为16.0 - 54.8 kg/m2）。用于补偿肥胖的方法对得出的红细胞容量、测量值升高的患者比例以及符合PCV标准的患者比例有显著影响。所有方法将患者分类为正常、升高或PCV的一致性仅为47.1%。
肥胖是红细胞容量测量解读中常见的混杂因素。目前发表的参考范围外推至肥胖患者时会产生不一致的结果。需要更多关于肥胖受试者的规范数据来确定哪种方法（如果有的话）是最佳的。
