The fluorescence patterns of antinuclear antibodies: morphological characteristics, immunological correlations and clinical significance

Most institutions adhere to the recommendations of the International Consensus on Antinuclear Antibody (ANA) Patterns (ICAP) for the nomenclature of ANA patterns and the standardization of laboratory reports. Some ANA patterns are frequently encountered in routine clinical laboratories, whereas others are rare. Additionally, certain patterns share highly similar morphological features and are therefore difficult to differentiate. Most ANA patterns are of high clinical relevance to the diagnosis of autoimmune diseases, while the clinical significance of certain patterns remains undefined. Each staining pattern corresponds to specific immunological epitopes. For different antigen targets within the same pattern, their clinical relevance may be partially comparable yet distinctly different in other aspects. Accurate identification of ANA patterns and comprehensive understanding of the clinical correlations among different patterns, as well as among distinct antigen targets of the same pattern, are of critical importance. Nevertheless, it remains challenging for laboratory analysts to distinguish subtle textural variations and other morphological characteristics of immunofluorescence staining patterns under light microscopy. Based on recent advances in relevant research, this review highlights the characteristic distinctions of morphologically similar ANA patterns, their immunological target antigens, and the similarities and differences in clinical relevance among various targets within an identical pattern. This review aims to assist laboratory professionals and clinicians in better identifying and interpreting ANA staining patterns, thereby optimizing the clinical application of HEp-2 indirect immunofluorescence (IFA) assays in the diagnostic workup of patients with suspected autoimmune diseases.