Serum neuron specific enolase (S-NSE) reference interval evaluation by time-resolved immunofluorometry compared with a radioimmunoassay

Abstract

The serum neuron specific enolase (S-NSE; EC 4.2. l.11) reference interval was evaluated by DELFIA (Wallac) in 161 healthy blood donors and the method compared with the S-NSE RIA assay (Pharmacia). The DELFIA assay total analytical variation coefficient (CV%) was between 3.7% and 6.6%., the RIA CV% 7.6% to 13.1%. Late centrifugation (after hours) increased the variation as a result of contamination with blood cells. Log transformation into a gaussian distribution was selected by Box-Cox analysis and tested by two models: the gauss-distribution and the Refval transformation. The 95% reference intervals and corresponding 90% confidence intervals were: female 2.9–9.6 μg/l (2.6–3.2 and 8.5–10.7) μg/l and male 3.4–11.7 μg/l (3.0–3.8 and 10.2–13.2 μg/l). Mean values were significantly different ( P < 0.001), female 5.3 (4.9–5.6), male 6.3 (5.8–6.7) μg/l. The serum NSE levels were analysed with both methods in a population of 110 patients. The results were significantly correlated (coefficient, 0.9896; r, 0.99; P < 0.0001 — two tailed). For high S-NSE values ( > 150.0 μg/1) differences between the methods exceeded the mean difference + 2S.D., while low concentrations were interconvertible. Maximal diagnostic efficacy was 0.91 for both assays, in DELFIA 17.2–23.9 pg/l and for RIA 17.2–21.9 pg/l. Identical sensitivity, specificity, discriminative power score, and likelihood ratio were found. The two methods are consequently interconvertible.