UACR a reliable alternative to 24hUP
The urine albumin-to-creatinine ratio (uACR) is an easy and reliable method of ruling out proteinuria >500 mg per day among patients with systemic light chain (AL) amyloidosis, performing relatively well against the 24-hour urine protein collection (24hUP) gold standard, a recent study has found.
The uACR also appears to be a good prognostic tool for renal outcomes and can help assess renal response to therapy.
A total of 575 patients (median age, 67 years; 64 percent male) participated in this retrospective study. All participants had paired 24hUP and uACR samples collected less than 7 days apart. The primary objective was to evaluate the correlation between 24hUP and uACR; the secondary goal was to validate the renal staging system, substituting uACR for 24hUP.
UACR correlated well with 24hUP in all patient subsets, including those whose samples were collected within 30 days of diagnosis (Pearson’s r, 0.87), or at any point during the course of their disease (Pearson’s r, 0.88).
Similarly, correlation was strong between systemic AL amyloidosis patients with estimated glomerular filtration rate <30 mL/min/1.73 m2 (Pearson’s r, 0.84) and proteinuria <3 g per day (Pearson’s r, 0.81).
Receiver operating characteristic curve analysis identified an optimal cutoff of >283 mg/g, at which value uACR had peak predictive capacity of 24hUP >500 mg. The resulting area under the curve (AUC) was 0.989, while sensitivity and specificity values were 94 percent and 97 percent, respectively. For 24hUP >5,000 g, the optimal uACR cutoff was 3,580 mg/g, yielding an AUC of 0.976, and a 94-percent sensitivity and specificity.
Finally, both uACR and 24hUP as measures of proteinuria were effective in determining the renal stage at disease diagnosis (k, 0.823).