Background Abnormal serum magnesium (Mg) concentrations are common and associated with worse mortality in kidney-transplant recipients. Many kidney and transplant-related factors affect Mg homeostasis. The concentration of the active form, ionized Mg (iMg), is not measured clinically, and total Mg (tMg) and iMg correlations have conflicted. We hypothesized that iMg and tMg concentrations show poor categorical agreement (i.e., low, normal, and high) in kidney-transplant recipients but that ionized calcium (iCa) correlates with iMg. Methods We retrospectively evaluated hypomagnesemia in kidney-transplant recipients over a 2-yr period. We prospectively collected blood at 0-28 days post-transplant to measure correlations between iMg and iCa/tMg. iMg and iCa concentrations in the reference ranges of 0.44-0.65 and 1.0-1.3 mmol/L, respectively, were considered normal. Fisher's exact test and unweighted kappa statistics revealed category agreements. Pearson's correlation coefficients and linear regression measured correlations. Results Among 58 retrospective kidney-transplant recipients, 54 (93%) had tMg<0.66 mmol/L, 28/58 (48%) received Mg supplementation, and 20/28 (71%) had tacrolimus dose adjustments during supplementation. In 13 prospective transplant recipients (N=43 samples), iMg and tMg showed strong category agreement (P=0.0003) and correlation (r=0.71, P<0.001), whereas iMg and iCa did not (P=0.7; r=-0.25, P=0.103, respectively). Conclusions tMg and iMg exhibited strong correlation following kidney transplantation. However, iCa may not be an accurate surrogate for iMg. Determining the effect of Mg supplementation and the Mg concentration where supplementation is clinically necessary are important next steps.

中文翻译：

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肾移植后儿科患者的离子镁与血镁总量相关。

背景 血清镁 (Mg) 浓度异常很常见，并且与肾移植受者死亡率恶化相关。许多肾脏和移植相关因素影响镁稳态。临床上并未测量活性形式离子镁 (iMg) 的浓度，并且总镁 (tMg) 和 iMg 的相关性存在冲突。我们假设肾移植受者中 iMg 和 tMg 浓度表现出较差的分类一致性（即低、正常和高），但离子钙 (iCa) 与 iMg 相关。方法 我们回顾性评估了肾移植受者两年内的低镁血症。我们前瞻性地在移植后 0-28 天采集血液，以测量 iMg 和 iCa/tMg 之间的相关性。iMg 和 iCa 浓度分别在 0.44-0.65 和 1.0-1.3 mmol/L 的参考范围内被认为是正常的。Fisher 的精确检验和未加权 kappa 统计揭示了类别一致性。皮尔逊相关系数和线性回归测量相关性。结果 58 例回顾性肾移植受者中，54 例（93%）tMg<0.66 mmol/L，28/58（48%）例接受镁补充剂，20/28（71%）例在补充剂期间调整他克莫司剂量。在 13 名预期移植受者（N=43 样本）中，iMg 和 tMg 显示出很强的类别一致性（P=0.0003）和相关性（r=0.71，P<0.001），而 iMg 和 iCa 则没有（P=0.7；r=- 0.25，P=0.103，分别）。结论 肾移植后 tMg 和 iMg 表现出很强的相关性。然而，iCa 可能不是 iMg 的准确替代品。确定镁补充剂的效果以及临床上需要补充镁的浓度是重要的后续步骤。