Ochsner Clinical School, The University of Queensland, New Orleans, Louisiana.
Department of Nephrology, Ochsner Health, New Orleans, Louisiana.
Kidney360. 2022 Jan 19;3(4):627-635. doi: 10.34067/KID.0005692021. eCollection 2022 Apr 28.
Fractional excretion of urinary sodium (FENa) is a widely utilized clinical test to evaluate acute kidney injury (AKI). A low FENa (<1%) is deemed consistent with prerenal azotemia and inconsistent with acute tubular injury (ATI). Muddy brown granular casts (MBGC) on microscopic examination of urinary sediment (MicrExUrSed) are highly suggestive of ATI. We hypothesized that there is poor concordance between the presence of MBGC and FENa in ATI.
We conducted a prospective observational study in patients with AKI seen during inpatient consultation. We extracted patients who underwent assessment of percentage of low power fields (LPFs) with MBGC by MicrExUrSed and concomitant measurement of FENa. Diagnostic concordance between MBGC and FENa and their individual prognostic value were examined.
Our cohort included 270 patients, 111 (41%) of whom were women. Median age was 61 years (range 27-92 years), and median serum creatinine was 3.7 mg/dl ( range1.2-22.0 mg/dl). MBGC were found in 49% (133/270). FENa <1% (inconsistent with ATI) was found in 50/133 (38%), 38/115 (33%), and 16/45 (36%) of those with >0%, ≥10%, and ≥50% LPFs with MBGC, respectively. Concordance between FENa and MBGC for ATI diagnosis was deemed fair (estimated -coefficient=0.2), and poor (=-0.11) within a subgroup of patients with preexisting chronic kidney disease (=139). In patients with biopsy-proven ATI (=49), MBGC had 100% specificity and 100% positive predictive value for ATI. MBGC were associated with greater risk for ≥50% increase in creatinine from baseline at discharge (acute kidney disease [AKD]).
About two of five patients with MBGC identified by MicrExUrSed presented with FENa <1%. Presence of MBGC was consistent with ATI, as verified by biopsy, and were predictive of AKD. These data suggest that the sole reliance in low FENa to exclude ATI should be abandoned, and MicrExUrSed should be pursued for AKI diagnosis.
尿钠排泄分数（FENa）是一种广泛用于评估急性肾损伤（AKI）的临床检测方法。低 FENa（<1%）被认为与肾前性氮质血症一致，与急性肾小管损伤（ATI）不一致。尿沉渣（MicrExUrSed）显微镜检查中出现棕色泥样颗粒管型（MBGC）高度提示 ATI。我们假设 MBGC 的存在与 ATI 中的 FENa 之间存在较差的一致性。
我们对住院会诊时出现 AKI 的患者进行了一项前瞻性观察性研究。我们提取了接受 MicrExUrSed 评估低倍视野（LPF）中 MBGC 百分比和同时测量 FENa 的患者。检查了 MBGC 与 FENa 之间的诊断一致性及其各自的预后价值。
我们的队列包括 270 名患者，其中 111 名（41%）为女性。中位年龄为 61 岁（范围 27-92 岁），中位血清肌酐为 3.7 mg/dl（范围 1.2-22.0 mg/dl）。270 名患者中有 49%（133/270）发现 MBGC。FENa <1%（与 ATI 不一致）在>0%、≥10%和≥50% LPF 中有 MBGC 的 133 名、115 名和 45 名患者中分别发现 50/133（38%）、38/115（33%）和 16/45（36%）。FENa 和 MBGC 对 ATI 诊断的一致性被认为是适度的（估计 -系数=0.2），而在预先存在的慢性肾脏病患者（=139）中则较差（=-0.11）。在活检证实的 ATI 患者（=49）中，MBGC 对 ATI 具有 100%的特异性和 100%的阳性预测值。MBGC 与出院时肌酐从基线增加≥50%的风险增加相关（急性肾损伤[AKD]）。
在通过 MicrExUrSed 鉴定的 MBGC 患者中，约有五分之二的患者 FENa <1%。MBGC 的存在与 ATI 一致，通过活检证实，并且预测 AKD。这些数据表明，仅依赖低 FENa 来排除 ATI 的方法应该被放弃，并且应该进行 MicrExUrSed 以进行 AKI 诊断。
