Elsevier

Clinica Chimica Acta

Volume 359, Issues 1–2, September 2005, Pages 109-114
Clinica Chimica Acta

Laboratory screening of connective tissue diseases by a new automated ENA screening assay (EliA Symphony) in clinically defined patients

https://doi.org/10.1016/j.cccn.2005.03.042Get rights and content

Abstract

Background

The measurement of antinuclear antibodies (ANA) is used in the autoimmune laboratory for the screening of connective tissue diseases (CTD). ANA measurements are mainly performed by indirect immunofluorescence (IIF) on HEp-2 cells or by enzyme immunoassay (EIA). The objective of this study was to clinically evaluate an automated EIA for extractable nuclear antigens (ENA) which lacks anti-dsDNA for the screening of CTD.

Methods

The study involved a total of 170 serum samples, 54 from patients with CTD, 26 from patients with other autoimmune diseases, and 90 from patients with non-autoimmune diseases. For all sera, ANA detection was performed by IIF and by EliA™ Symphony (Pharmacia Diagnostics, Freiburg, Germany), an ENA screening which detects the following autoantibodies: SSA/Ro, SSB/La, U1RNP (70 kDa, A, C), Scl-70, JO-1, centromere B and Sm. Also, anti-dsDNA (EliA™ dsDNA, Pharmacia Diagnostics, Freiburg, Germany) was measured on all samples. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), efficiency, positive likelihood ratio (PLR), and negative likelihood ratio (NLR) were calculated.

Results

Diagnostic efficiency was similar for IIF (82.6%) and EliA™ Symphony (82.3%), as well as PLR (6.5 for IIF, and 7.3 for EliA™ Symphony), and NLR (0.35 for IIF, and 0.41 for EliA™ Symphony). The combined measurement of EliA™ Symphony and dsDNA increased sensitivity but not PLR. Area under receiver operator characteristic (ROC) curve was similar for IIF (0.847) and EliA™ Symphony (0.823).

Conclusions

The results of the study demonstrate that EliA™ Symphony solely or combined with anti-dsDNA detection has an efficiency similar to HEp-2 cells IIF with a cut-off of 1:160 for the diagnosis of CTD.

Introduction

The measurement of antinuclear antibodies (ANA) is used in the autoimmune laboratory for the screening of connective tissue diseases (CTD). ANA measurement are performed by indirect immunofluorescence (IIF) assay on cultured human epidermoid carcinoma cells (HEp-2 cells) [1]. However ANA-IIF is a time consuming procedure, difficult to automatize and standardize, and with poor reproducibility due to the subjective interpretation of results. After ANA-IIF positive results are subjected to ENA screening by enzyme immunoassay (EIA).

In the last few years, EIA kits have been developed for ANA and ENA screening, with the objective of replacing ANA-IIF and ENA screening by ANA–EIA. Commercially available kits for ANA determination use HEp-2 nuclear extracts, HEp-2 nuclear extracts plus purified or recombinant antigens, or purified and/or recombinant antigens. Comparison studies between ANA–IIF and ANA–EIA have been performed with discordant results [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], in part due to the antigenic composition of EIA screening reagents.

The objective of the present study was to evaluate an automated detection system for ENA screening which lacks anti-dsDNA for detection of connective tissue diseases (CTD) and to compare it with the classical HEp-2 cell ANA.

Section snippets

Samples

A total of 170 serum samples were included in the study. The diagnosis of the patients was: CTD (n = 54), other autoimmune diseases (other-AD) (n = 26) and non-autoimmune diseases (non-AD) (n = 90). All patients came from specialized centers and were characterized with respect to gender, age, diagnosis and treatment. So, the study design did not reflect the routine situation; instead, groups were constructed artificially from well-defined, pre-characterized patients. The CTD group consisted of

Results

A summary of the results obtained is shown in Table 1. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), efficiency and positive and negative likelihood ratios are shown in Table 2. A sensitivity of 69% (95% CI: 56–81%) was obtained for HEp-2 IIF, and a slightly lower value of 63% (95% CI: 50–76%) for EliA™ Symphony. The combination of EliA™ Symphony and EliA™ dsDNA gave a sensitivity of 74% (95% CI: 62–85%). A specificity of 89% (95% CI: 84–95%) was

Discussion

In this study we compared the clinical diagnostic efficiency of ANA analyzed by IIF with that obtained with a new automated ENA screening enzyme immunoassay (EliA™ Symphony), which lacks anti-dsDNA in patients with CTD. In the predefined set of patients analyzed, the performance of the two techniques was very comparable. Efficiency was on the same level (∼ 82%) as were positive and negative likelihood ratios. Surprisingly, the combined use of EliA™ Symphony which lacks anti-dsDNA with EliA™

References (17)

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