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 Two recent articles in JASN--one by Siew et al and the other by Paragas et al--provide further support to the idea of using urinary NGAL as a biomarker for acute kidney injury. An accompanying editorial by Lynda Szczech , entitled, "The Development of Urinary Biomarkers for Kidney Disease Is the Search for Our Renal Troponin", provides a thoughtful analogy for thinking about how best to use these tests. The author emphasizes that biomarkers will not necessarily replace creatinine and urine output as a means of assessing AKI--but rather it will supplement these more traditional tests, much like troponin is now used in conjunction with older methods (e.g., EKG analysis) is diagnosing myocardial injury. A marker such as urinary NGAL may be a better marker for injury, as serum creatinine is really a marker of kidney function, and becomes elevated far after the kidney insult.In the study by Siew et al , over 400 critically ill patients underwent urinary NGAL measurement within 24 hours of admission to an ICU; these patients were then followed prospectively and assessed for AKI, as defined by an increase in serum creatinine of greater than 0.3mg/dL or a greater than 50% increase in the baseline creatinine. The investigators found that elevated urinary NGAL levels was moderately successful in predicting AKI. In the second study by Paragas et al , investigators looked at the ability of urinary NGAL to distinguish between HIV patients with a collapsing FSGS pathology (e.g., "HIVAN") compared to HIV patients that had either normal kidney function or CKD from another cause. Importantly, patients with HIVAN had 11-fold higher urinary NGAL levels compared to HIV-positive controls without a reduced GFR, and still 5.5-fold higher urinary NGAL levels compared to HIV-positive controls with CKD due to a cause other than HIVAN. These findings may prove useful in terms of diagnosing patients with HIV and rapidly declining renal function with HIVAN in a non-invasive manner (e.g., no biopsy). While biopsy should still likely remain the gold standard until these findings can be confirmed with a larger n, it could potentially be useful information in patients where biopsy is deemed too risky to proceed--a situation in which HIVAN patients may commonly find themselves.
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