Faculty of Medicine, University of Toronto, Ottawa, Canada.
Clinical Epidemiology Program, The Ottawa Hospital Research Institute, Ottawa, Canada.
Clin Chem Lab Med. 2020 Nov 19;59(5):869-874. doi: 10.1515/cclm-2020-1286. Print 2021 Apr 27.
The value of the serum protein gap (PG, difference between total protein and albumin) in the detection of hyper- or hypogammaglobulinemia is not well established. We assessed the performance of PG for the detection of hyper- or hypogammaglobulinemia in a large sample of patients.
We reviewed all paired measurements of serum total protein, albumin, quantitative immunoglobulins, and serum protein electrophoresis tested between March 2014 and June 2017 at the Eastern Ontario Regional Laboratory Association. Sensitivity, specificity, positive predictive value, negative predictive value and likelihood ratios of PG at thresholds between 18 and 44 g/L for the detection of hyper- and hypogammaglobulinemia were assessed.
There were 19,575 and 5,426 simultaneous paired data points to assess hyper- and hypogammaglobulinemia identified by serum protein electrophoresis (SPE) and nephelometry, respectively. The mean PG was 36.3 g/L (SD 8.6). The prevalence of hypergammaglobulinemia (>16 g/L by SPE) and hypogammaglobulinemia (IgG <7 g/L) was 21.9 and 5.5%, respectively. High PG (≥38 g/L) had sensitivity and specificity of 76.2 and 71.5% respectively for hypergammaglobulinemia. PG ≥38 g/L had a negative predictive value (NPV) of 93.1% for monoclonal, and 96.9% for polyclonal gammopathy. A PG threshold of ≤18 g/L had of sensitivity of 0.4%, specificity of 100%, PPV of 100% and NPV of 80.1% to detect hypogammaglobulinemia (IgG <7 g/L).
High and low PG values were not sensitive in detecting hyper- or hypogammaglobulinemia, although negative predictive values were high for both. Performance of PG should be further evaluated prospectively in specific populations at risk of for abnormal IgG levels.
血清蛋白间隙（PG，总蛋白与白蛋白之差）在高或低γ球蛋白血症检测中的价值尚未得到充分确立。我们评估了 PG 在大量患者中检测高或低γ球蛋白血症的性能。
我们回顾了 2014 年 3 月至 2017 年 6 月期间在安大略省东部地区实验室协会进行的所有血清总蛋白、白蛋白、定量免疫球蛋白和血清蛋白电泳的配对检测。评估了 PG 在 18 至 44 g/L 之间的阈值下检测高和低γ球蛋白血症的敏感性、特异性、阳性预测值、阴性预测值和似然比。
分别通过血清蛋白电泳（SPE）和散射比浊法评估了 19575 个和 5426 个同时的配对数据点以确定高和低γ球蛋白血症。PG 的平均值为 36.3 g/L（SD 8.6）。SPE 检测到的高γ球蛋白血症（>16 g/L）和低γ球蛋白血症（IgG <7 g/L）的患病率分别为 21.9%和 5.5%。高 PG（≥38 g/L）对高γ球蛋白血症的敏感性和特异性分别为 76.2%和 71.5%。PG ≥38 g/L 对单克隆和多克隆γ球蛋白血症的阴性预测值（NPV）分别为 93.1%和 96.9%。PG 阈值≤18 g/L 对低γ球蛋白血症（IgG <7 g/L）的敏感性为 0.4%，特异性为 100%，阳性预测值为 100%，NPV 为 80.1%。
高和低 PG 值在检测高或低γ球蛋白血症时不敏感，尽管两者的阴性预测值均较高。PG 的性能应在特定的高危人群中进行前瞻性评估。
