Department of Pediatrics, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8583, Japan.
Department of Pediatrics, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8583, Japan.
Clin Biochem. 2024 Oct;131-132:110807. doi: 10.1016/j.clinbiochem.2024.110807. Epub 2024 Jul 24.
Fractional excretion of magnesium (FE) is commonly used to diagnose of renal magnesium (Mg) wasting, but it can be affected by serum Mg (SMg) and serum creatinine concentration (SCr). We investigated the sensitivity and specificity of FE to diagnose Mg wasting in subgroups with different SMg and eGFR (estimated glomerular filtration rate) in pediatric nephrology practice.
One hundred and nineteen patients (59 males and 60 females, median 15 years) seen in our pediatric clinic were investigated for FE, SMg, eGFR, and urine Mg-to-creatinine ratio (Mg/Cr). Normal eGFR was defined as ≥ 90 ml/min/1.73 m or for infants SCr < chronic kidney disease stage 2. Urine Mg/Cr was compared with age-specific reference values.
Sixteen of all patients (13 %) had hypomagnesemia. All had FE greater than the cut-off value of 2 %. Only 4 patients had elevated urine Mg/Cr. Of 65 patients with normal SMg and eGFR, 19 had FE above the cut-off value of 4 %. Of these, 13 patients had elevated urine Mg/Cr i.e. Mg wasting (sensitivity and specificity of FE, 93 % and 88 %, respectively). Among 38 patients with normal SMg and low eGFR, 30 had FE > 4 %, but only 6 had elevated urine Mg/Cr (sensitivity 100 % and specificity 25 %). Overall, hypomagnesemic patients and normomagnesemic patients with elevated urine Mg/Cr were diagnosed with Mg wasting (36/119, 30 %).
FE has variable sensitivity and specificity depending on SMg and eGFR in the diagnosis of Mg wasting. Mg wasting is not uncommon in pediatric nephrology practice.
镁的分数排泄率（FE）常用于诊断肾脏镁（Mg）丢失，但它可能会受到血清镁（SMg）和血清肌酐浓度（SCr）的影响。我们研究了在儿科肾病实践中不同 SMg 和估算肾小球滤过率（eGFR）亚组中，FE 诊断 Mg 丢失的敏感性和特异性。
对我院儿科门诊 119 例患者（男 59 例，女 60 例，中位数 15 岁）进行 FE、SMg、eGFR 和尿镁/肌酐比值（Mg/Cr）检查。正常 eGFR 定义为≥90 ml/min/1.73 m 或婴儿 SCr<慢性肾脏病 2 期。尿 Mg/Cr 与年龄特异性参考值进行比较。
所有患者中（13%）有 16 例低镁血症。所有患者的 FE 均大于 2%的截断值。仅有 4 例患者尿 Mg/Cr 升高。在 65 例 SMg 和 eGFR 正常的患者中，19 例 FE 高于 4%的截断值。其中，13 例患者尿 Mg/Cr 升高，即存在 Mg 丢失（FE 的敏感性和特异性分别为 93%和 88%）。在 38 例 SMg 正常而 eGFR 较低的患者中，30 例 FE>4%，但仅有 6 例尿 Mg/Cr 升高（敏感性 100%，特异性 25%）。总的来说，低镁血症患者和尿 Mg/Cr 升高的正常镁血症患者被诊断为 Mg 丢失（119 例患者中 36 例，30%）。
FE 诊断 Mg 丢失的敏感性和特异性随 SMg 和 eGFR 而变化。在儿科肾病实践中，Mg 丢失并不少见。
