medwireNews: The ratio of absolute neutrophil to lymphocyte count could be an effective additional biomarker for detecting infection in patients with systemic lupus erythematosus (SLE), research suggests.
Accurately diagnosing whether a patient has an infection or lupus flare can be difficult due to overlap of markers for both conditions, point out the investigators. But they add that it is “vital,” given that the former requires reduction of immunosuppressive drugs whereas the latter requires an increase or replacement with a more potent drug.
Among 120 patients with SLE, aged an average of 33 years, 60 patients were admitted to hospital with disease flare and 60 due to infection. The neutrophil-to-lymphocyte ratio (NLR) was significantly higher in the latter patients, at 14.2 versus 3.3 in those with disease flare.
The marker correlated positively with C-reactive protein (CRP) levels – a recognized biomarker for SLE infection – and both were significantly associated with infection in logistic regression analyses, with odds ratios of 1.62 and 2.91, respectively.
Researcher Chang-Hee Suh and team, from Ajou University School of Medicine in Suwon, South Korea, also studied the diagnostic potential of the platelet-to-lymphocyte ratio (PLR) and the monocyte-to-lymphocyte ratio (MLR).
But while the PLR was significantly increased in SLE patients with infection relative to those with flare and correlated positively with CRP levels, it was not significantly associated with infection. And the MLR did not differ significantly between the two patient groups.
In receiver operating characteristic curve analysis, NLR, at a cutoff of 5.70 and an area under the characteristic curve of 0.87, had good sensitivity and specificity for diagnosing infection, at a respective 75% and 90%.
This was less effective than CRP levels, which at a cutoff level of 1.28 mg/dL and an AUC of 0.942, had 93.3% sensitivity and 91.7% specificity.
But the authors note in Clinical Rheumatology that when NLR and CRP levels were combined specificity improved beyond that seen with CRP alone to 96.7%, although the difference was not statistically significant.
“CRP, neutrophil and lymphocyte count has been commonly used in clinical practice and it is relatively simple to perform. Therefore, NLR could be used additionally to distinguish infection from disease flare in SLE,” write Suh and co-authors.
The data also showed, however, only a weak association between NLR and SLE disease activity index scores and no association between NLR and other disease activity markers, such as complement 3 and 4, and anti-dsDNA, making it a poor marker for evaluating disease activity.
By Lucy Piper
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