Thompson Kimberly A, Rayburn Marie C, Chigerwe Munashe
J Am Vet Med Assoc. 2017 Sep 15;251(6):702-705. doi: 10.2460/javma.251.6.702.
OBJECTIVE To evaluate the usefulness of serum immunocrit measurement to detect failure of passively acquired immunity (FPI) in dairy calves. DESIGN Diagnostic test evaluation. ANIMALS 249 female dairy calves (age, 2 to 6 days). PROCEDURES A blood sample was collected from each calf, and serum was harvested. Immunocrit was measured in serum samples by use of 55% ammonium sulfate solution and the standard technique. Serum IgG concentration was measured by means of radial immunodiffusion (reference standard), with FPI defined as a result < 1,000 mg/dL. The immunocrit value (cutpoint) that maximized both sensitivity and specificity of the method for detection of FPI was determined by construction of receiver operating characteristic curves, and likelihood ratios for positive and negative test results were calculated. RESULTS Immunocrit values were significantly correlated (ρ = 0.71) with serum IgG concentration as measured by radial immunodiffusion. An immunocrit cutpoint of 11% was optimal for detection of FPI in the calves. Sensitivity and specificity of the immunocrit method at this cutpoint were 0.88 (95% confidence interval [CI], 0.79 to 0.97) and 0.51 (95% CI, 0.44 to 0.58), respectively. Likelihood ratios for positive and negative test results were 1.80 (95% CI, 1.51 to 2.14) and 0.23 (95% CI, 0.11 to 0.51), respectively. CONCLUSIONS AND CLINICAL RELEVANCE The immunocrit method was useful for identifying dairy calves with FPI and was simple and could be quickly performed. Because precipitation of immunoglobulins by ammonium sulfate is not species specific, the immunocrit method should be evaluated for detection of FPI in other veterinary species as well.
目的 评估血清免疫比容测定在检测奶牛犊牛被动获得性免疫失败（FPI）中的作用。 设计 诊断试验评估。 动物 249 头雌性奶牛犊牛（年龄 2 至 6 天）。 程序 从每头犊牛采集血样并收获血清。 使用 55%硫酸铵溶液和标准技术测定血清免疫比容。 通过放射免疫扩散法（参考标准）测定血清 IgG 浓度，FPI 定义为结果<1000mg/dL。 通过构建受试者工作特征曲线确定使检测 FPI 方法的敏感性和特异性最大化的免疫比容值（切点），并计算阳性和阴性试验结果的似然比。 结果 免疫比容值与放射免疫扩散法测定的血清 IgG 浓度显著相关（ρ = 0.71）。 免疫比容切点为 11%时最适合检测犊牛的 FPI。 此切点下免疫比容法的敏感性和特异性分别为 0.88（95%置信区间[CI]，0.79 至 0.97）和 0.51（95%CI，0.44 至 0.58）。 阳性和阴性试验结果的似然比分别为 1.80（95%CI，1.51 至 2.14）和 0.23（95%CI，0.11 至 0.51）。 结论及临床意义 免疫比容法有助于识别患有 FPI 的奶牛犊牛，且方法简单、可快速实施。 由于硫酸铵沉淀免疫球蛋白不具有种属特异性，免疫比容法也应评估用于检测其他兽医物种的 FPI。
