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Antinuclear antibodies (ANAs) are valuable laboratory markers to screen for and support the diagnosis of various rheumatic diseases (known as ANA-associated rheumatic diseases). The importance of ANA testing has been reinforced by the inclusion of ANA positivity as an entry criterion in the 2019 systemic lupus erythematosus classification criteria. In addition, specific ANAs (such as antibodies to Sm, double-stranded DNA (dsDNA), SSA/Ro60, U1RNP, topoisomerase I, centromere protein B (CENPB), RNA polymerase III and Jo1) are included in classification criteria for other rheumatic diseases. A number of techniques are available for detecting antibodies to a selection of clinically relevant antigens (such as indirect immunofluorescence and solid phase assays). In this Review, we discuss the advantages and limitations of these techniques, as well as the clinical relevance of the differences between the techniques, to provide guidance in understanding and interpreting ANA test results. Such understanding not only necessitates insight into the sensitivity and specificity of each assay, but also into the importance of the disease context and antibody level. We also highlight the value of titre-specific information (such as likelihood ratios).

Anti-nuclear antibodies (ANA) are fundamental for the diagnosis of autoimmune diseases, and have been determined by indirect immunofluorescence assay (IIFA) for decades. As the demand for ANA testing increased, alternative techniques were developed challenging the classic IIFA. These alternative platforms differ in their antigen profiles, sensitivity and specificity, raising uncertainties regarding standardisation and interpretation of incongruent results. Therefore, an international group of experts has created recommendations for ANA testing by different methods. Two groups of experts participated in this initiative. The European autoimmunity standardization initiative representing 15 European countries and the International Union of Immunologic Societies/World Health Organization/Arthritis Foundation/Centers for Disease Control and Prevention autoantibody standardising committee. A three-step process followed by a Delphi exercise with closed voting was applied. Twenty-five recommendations for determining ANA (1-13), anti-double stranded DNA antibodies (14-18), specific antibodies (19-23) and validation of methods (24-25) were created. Significant differences between experts were observed regarding recommendations 24-25 (p<0.03). Here, we formulated recommendations for the assessment and interpretation of ANA and associated antibodies. Notably, the roles of IIFA as a reference method, and the importance of defining nuclear and cytoplasmic staining, were emphasised, while the need to incorporate alternative automated methods was acknowledged. Various approaches to overcome discrepancies between methods were suggested of which an improved bench-to-bedside communication is of the utmost importance. These recommendations are based on current knowledge and can enable harmonisation of local algorithms for testing and evaluation of ANA and related autoantibodies. Last but not least, new more appropriate terminologies have been suggested.

The impact of autoimmune diseases is growing from both a clinical and a laboratory point of view. Diagnostic assays are now being transferred from dedicated specialised laboratories into high-throughput service laboratories. The increasing number of available methods has raised the variability among the laboratories, making their reproducibility a critical problem. On the other hand, reliable tests are needed for early diagnosis and prompt treatment, and the cost of repeated confirmatory tests should be reduced and unnecessary further investigations avoided. New methodologies, particularly for antinuclear antibodies (ANAs), have been applied to autoantibody detection in order to screen and process larger volumes of clinical specimens more quickly and at less cost than the traditional methods. However, because of the lack of their sensitivity to detect all ANAs and standardisation, inaccuracies (including false positives and negatives) in the results have been reported. A committee of the American College of Rheumatology was formed to address this issue. Specific recommendations have been suggested that represent a realistic first step in the standardisation of diagnostic tests for autoimmune diseases.

The symptoms of fibromyalgia and lupus can be similar, but the treatments are very different. Although the antinuclear antibody (ANA) test has often been used to make the distinction, this approach has its pitfalls. This paper offers strategies for more accurate diagnosis.

This study was performed by the Italian Society of Laboratory Medicine (SIMeL) in order to establish the variability between the different analytical systems currently used in clinical laboratories for the detection of autoantibodies diagnostic of systemic autoimmune disease. Sixteen industrial, and two university laboratories participated in this study which entailed the determination of anti-nuclear (ANA), anti-dsDNA and anti-ENA antibodies in 11 sera from patients with clinically diagnosed systemic rheumatic disease, using reagents produced by these companies and different methodologies (indirect immunofluorescence, immunoenzymatic assay, counterimmunolectrophoresis, immuno and western blotting). We found 93.5% agreement between the methods used for the detection of ANA, 85.2% for anti-dsDNA antibodies, and 86.9% for anti-ENA antibodies. Among the anti-ENA antibodies, regardless of the method used, detection percentages were excellent for anti-RNP and anti-SSB/La (100%), good for anti-SSA/Ro (93%), but unacceptable for the anti-Jo-1 (67%), anti-Scl70 and anti-Sm (47%) antibodies. This further stresses the need for rigorous standardisation of commercial reagents and analytical procedures, as well as the introduction of external quality assessment (EQA) programs, and a complete definition of operative protocols adjusted to the sensitivity and specificity of the various methods.

Considerable progress has been made in the improvement of clinical assays for the detection of autoantibodies to nuclear and intracellular antigens with the use of available World Health Organization (WHO) and Arthritis Foundation/Centers for Disease Control (AF/CDC) standards. The ultimate goal of standardization is for various clinical laboratory test results to be interchangeable and for an exchange of data to be done with confidence. This report discusses the available standards. In addition, significant technical problems and variations in methodologies for the detection of autoantibodies to intracellular antigens noted during a 4-year study by a European Consensus Study Group are detailed. Currently, there is a need for a future generation of reference preparations and standards that will show specific antibody reactivity on sensitive enzymes and immunoblotting assays. Standardization efforts should be done to characterize specific nuclear and cellular antigen preparations that may be of natural or of recombinant technology origin.