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.