The spectrum of nuclear patterns with stained metaphase chromosome plate: morphology nuances, immunological associations, and clinical relevance.

The indirect immunofluorescence assay (IFA) on HEp-2 cells is the prevailing method used to screen for autoantibodies in the investigation of systemic autoimmune diseases (SAID). When positive, the titer provides a semi-quantitative assessment of the autoantibody serum concentration whereas the immunofluorescence pattern indicates the possible autoantibody specificities. The Brazilian Consensus on ANA Patterns (BCA) and the International Consensus on ANA Patterns (ICAP) provide recommendations for the harmonization on the pattern nomenclature and test reporting. Nuclear patterns are among the most frequent in the clinical laboratory and some of them are highly relevant in the diagnosis of SAID. Nuclear patterns with stained metaphase plate (MP) indicate autoantibodies against chromatin components or against chromatin-bound antigens. These include the nuclear homogeneous (AC-1), nuclear dense fine speckled (AC-2), Topo 1-like (AC-29), and nuclear fine speckled with stained MP (AC-30) patterns. The Brazilian consensus has also classified the -homogeneous nuclear pattern (QH). The correct identification of these patterns is important because each one is associated with different autoantibody specificities and clinical scenarios. However, the recognition of the nuances in texture of the staining pattern and other specific features that characterize each of them may be challenging for the analyst at the microscope. This review focuses on the morphological characteristics, immunological identities, and clinical relevance of nuclear patterns with stained MP. The aim is to assist laboratory analysts and clinicians in identifying and interpreting these patterns, thus optimizing the use of the HEp-2 IFA test in the investigation of patients under suspicion of SAID.