Antinuclear Antibodies

An antinuclear antibody test detects autoantibodies against self-antigens in the nucleus, cytoplasm and mitotic apparatus. The name is therefore narrower than the biology. International Consensus on ANA Patterns (ICAP) increasingly favours anti-cell antibodies because cytoplasmic and mitotic reactivity can carry important diagnostic information. The reference method is indirect immunofluorescence on a HEp-2 human epithelial cell substrate. HEp-2 cells display approximately 100–150 autoantigens in a near-native arrangement, allowing the laboratory to report two linked findings: - a reciprocal titre, such as 1:80, 1:320 or 1:1,280; and - a staining pattern, reported using ICAP’s alphanumeric AC code when available. The titre is a measure of how far the patient’s serum can be diluted before the fluorescence is no longer detected. A higher titre increases the probability of an ANA-associated systemic rheumatic disease, but no titre diagnoses SLE, systemic sclerosis, Sjögren disease or any other condition by itself. A starting screening dilution of 1:80 is the current consensus threshold. Using a lower cut-off such as 1:40 identifies many more healthy people without meaningfully improving clinical sensitivity. ANA positivity is common without autoimmune disease;...