Department of Animal Science, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.
J Dairy Sci. 2017 Nov;100(11):9285-9293. doi: 10.3168/jds.2017-12971. Epub 2017 Sep 13.
The objectives of this study were to (1) compare a test for serum measurement of total Ca (tCa), Mg, and P (VetTest Chemistry Analyzer, IDEXX Laboratories Inc., Westbrook, ME) to reference methods (spectrophotometric assays on a Beckman Coulter 640e automated clinical chemistry analyzer; Beckman Coulter, Brea, CA), (2) determine the relationship between ionized Ca (iCa) and reference method tCa in the immediate postpartum period, and (3) assess the relative value of these blood Ca indices as predictors of neutrophil oxidative burst activity. Samples were collected from multiparous Holstein cows (n = 33) over the first 5 d in milk. A total of 183 samples for objective 1 and 181 samples for objective 2 were available. Neutrophil oxidative burst activity was assessed once between 2 and 5 d in milk (n = 29). Linear regression demonstrated strong relationships between serum tCa, Mg, and P concentrations measured by the VetTest compared with the reference method. Bland Altman analysis indicated that the VetTest values were higher than the reference method by 0.22 mmol/L for tCa, 0.12 mmol/L for Mg, and 0.16 mmol/L for P. Compared with hypocalcemia categorized at ≤2.0 or ≤2.125 mmol/L with the reference method tCa, thresholds for the VetTest measured tCa of ≤2.23 mmol/L (sensitivity = 87%, specificity = 89%) or ≤2.30 mmol/L (sensitivity = 86%, specificity = 96%) could be used. The relationship between whole-blood iCa and reference method serum tCa differed by sampling time point after calving. Compared with identification of hypocalcemia with serum tCa measurements from the reference method (thresholds of ≤2.0 and 2.125 mmol/L), a whole-blood iCa threshold of ≤1.17 mmol/L resulted in the highest combined sensitivities (94 and 82%) and specificities (80 and 94%) at either threshold. Ionized Ca measurements were more consistently related to outcomes of neutrophil oxidative burst activity measured in vitro. The VetTest measurements of serum tCa reliably identified hypocalcemia when thresholds were adjusted to account for the bias of the test. The variation in the relationship between iCa and reference method tCa in the days following parturition suggest that these measures cannot be used interchangeably as indicators of Ca status. The more consistent associations between iCa and in vitro measures of neutrophil function, compared with tCa, indicated that this may be a more sensitive predictor of functional outcomes associated with postpartum Ca status.
(1) 比较一种用于检测血清总钙 (tCa)、镁和磷的测试方法（VetTest Chemistry Analyzer，IDEXX Laboratories Inc.，Westbrook，ME）与参考方法（贝克曼库尔特 640e 自动化临床化学分析仪上的分光光度法；贝克曼库尔特，Brea，CA）；(2) 确定产后即刻离子钙 (iCa) 与参考方法 tCa 的关系；(3) 评估这些血钙指标作为预测中性粒细胞氧化爆发活性的相对价值。对 33 头经产荷斯坦奶牛在产犊后第 1 至 5 天期间采集了样本。共有 183 份样本用于目标 1，181 份样本用于目标 2。在产犊后 2 至 5 天之间（n=29）对中性粒细胞氧化爆发活性进行了一次评估。线性回归显示，VetTest 检测的血清 tCa、Mg 和 P 浓度与参考方法之间存在很强的关系。Bland-Altman 分析表明，VetTest 值比参考方法高 0.22 mmol/L 的 tCa、0.12 mmol/L 的 Mg 和 0.16 mmol/L 的 P。与参考方法 tCa 分类的低钙血症（≤2.0 或 ≤2.125 mmol/L）相比，VetTest 测量的 tCa 的阈值为≤2.23 mmol/L（敏感性=87%，特异性=89%）或≤2.30 mmol/L（敏感性=86%，特异性=96%）可用于识别低钙血症。产后不同时间点全血 iCa 与参考方法血清 tCa 的关系不同。与参考方法血清 tCa 测量值识别低钙血症（阈值为≤2.0 和 2.125 mmol/L）相比，全血 iCa 阈值为≤1.17 mmol/L 可获得最高的联合敏感性（94%和 82%）和特异性（80%和 94%）。离子钙的测量结果与体外中性粒细胞氧化爆发活性的测量结果更一致。当调整 VetTest 检测的阈值以适应检测的偏差时，血清 tCa 的检测结果可靠地识别出低钙血症。产犊后几天内 iCa 与参考方法 tCa 之间关系的变化表明，这些指标不能作为 Ca 状态的指示物互换使用。与 tCa 相比，iCa 与体外中性粒细胞功能测量之间更一致的关联表明，这可能是产后 Ca 状态相关功能结果的更敏感预测指标。
