JAMA Ophthalmol 2014.
NEW YORK (Reuters Health) – The combination of urinary beta-2-microglobulin and serum creatinine is a sensitive diagnostic screening tool for diagnosing tubulointerstitial nephritis and uveitis (TINU) syndrome in young patients with uveitis, researchers from the Netherlands report.
Only 1% to 2% of all patients at specialized uveitis centers have TINU syndrome, which can lead to severe renal damage, they write in JAMA Ophthalmology, online October 30.
An increased urinary level of beta-2-microglobulin has been proposed as a potential screening tool for detecting acute interstitial nephritis (AIN) in order to reduce the number of diagnostic renal biopsies that are required for the diagnosis of TINU syndrome.
Dr. Ymkje M. Hettinga from University Medical Center Utrecht and colleagues investigated the predictive value of this marker as well as urinary protein in a study of 45 consecutive patients with uveitis.
Forty percent of patients had elevated urinary beta-2-microglobulin levels (mean, 6.52 mg/L), 22% had increased serum creatinine levels (mean, 1.15 mg/dL) and 47% had proteinuria, the researchers found.
Seven of eight patients with definite or probable TINU syndrome had beta-2-microglobulin levels of 1.0 mg/L or higher, and the median levels of urinary beta-2-microglobulin were significantly higher in these eight patients (1.95 mg/L) than in the patients with normal renal function (0.20 mg/L).
For a urinary beta-2-microglobulin level greater than 0.20 mg/L, the positive predictive value for TINU syndrome was 39%, and the negative predictive value was 96%. The PPV increased to 88% and the NPV to 97% for a cutoff of 1.0 mg/L.
By comparison, the PPV of increased serum creatinine for predicting TINU syndrome was 80%, and the NPV was 100% whereas the PPV and NPV of proteinuria were only 30% and 91%.
Combining elevated beta-2-microglobulin and elevated serum creatinine increased the PPV to 100% with an NPV of 97%.
“To identify the specific AIN in children with uveitis, thereby potentially leading to the diagnosis of TINU syndrome, we recommend that all young patients with bilateral anterior uveitis with or without intermediate or posterior involvement of unknown origin should be tested for both urinary beta-2-microglobulin and serum creatinine,” the researchers conclude.
“These data suggest that urinary beta-2-microglobulin and serum creatinine levels are a sensitive and relatively simple diagnostic screening tool for detecting renal dysfunction to diagnose TINU syndrome in young patients with uveitis similar to those evaluated in this study,” they add.
Dr. Hettinga did not respond to a request for comments.
JAMA Ophthalmol 2014.