ANA Test: How to Read a Positive Antinuclear Antibody Result

A typical result reads something like "positive, 1:160, speckled". The reference method, called indirect immunofluorescence, dilutes the blood serum step by step and checks after each step whether the nuclei of cultured cells (HEp-2 cells) still glow under a microscope.

• The titer is the most diluted step at which the glow can still be seen. A faint signal disappears after one or two steps and reads 1:40; a strong one survives to 1:640 or beyond. It shows how strong the signal is, not an amount of antibody.
• The pattern is the shape the glow makes inside the nucleus, such as homogeneous or speckled, and it hints at which specific antibody is present.

Some labs screen with an ELISA or bead-based test instead. These report an index or units with no titer or pattern, and the two kinds of result cannot be converted into each other. The 2019 EULAR/ACR lupus classification criteria accept either method, provided the solid-phase test performs at least as well, so the method is worth noting alongside the result.

Those figures come from a 1997 study in which fifteen reference laboratories tested samples from healthy donors. Positive results became more common with age, especially in women over 65. The guide to flagged values explains why a test designed to miss almost no cases produces so many flags in healthy people.

Because the symptoms that prompt an ANA are common, the test picks up many positives that have nothing to do with lupus:

• other autoimmune conditions, including Sjögren's syndrome, scleroderma, rheumatoid arthritis and autoimmune thyroid disease;
• a recent or ongoing viral infection, where the antibodies are usually temporary;
• some medicines, which can cause a drug-induced positive ANA that fades after the drug is stopped (no medicine should be stopped without the prescriber);
• older age, and in many people no identifiable reason at all.

The same titer can mean opposite things in different people. A 1:640 in someone who feels well and a 1:80 in someone with a butterfly-shaped rash across the cheeks and swollen joints are read very differently.

The International Consensus on ANA Patterns (ICAP) gives each pattern a code from AC-1 to AC-29. Patterns are judged by a person at a microscope, and two labs can describe the same slide differently, so a pattern guides the next test rather than settling anything.

AC-2 is the one pattern where a high titer points away from disease: when anti-DFS70 is the only antibody found and nothing else suggested an autoimmune disease, it is commonly seen in healthy people. Nucleolar patterns (AC-8 to AC-10), with the glow concentrated in small bodies inside the nucleus, are classically linked with systemic sclerosis.

The next step is finding out which specific antibody caused the positive result, because that is what maps to a named disease. The American College of Rheumatology's Choosing Wisely advice is that tests such as anti-dsDNA, Smith, RNP, SSA, SSB, Scl-70 and centromere should not be ordered without a positive ANA and a clinical reason, because they are almost always negative when the ANA is negative.

Depending on the pattern and symptoms, follow-up usually includes the extractable nuclear antigen (ENA) panel, which covers the Smith antibody, RNP, anti-SSA and anti-SSB; complement proteins C3 and C4, which help show whether lupus is active; and ESR and CRP for inflammation.

When joints are the main problem, anti-CCP and rheumatoid factor test for rheumatoid arthritis. When there is a history of blood clots, anticardiolipin antibodies and the other antiphospholipid tests are often added. A low-titer positive with no symptoms is often simply watched, which is a reasonable plan rather than a dismissal. The guide to reading an autoimmune panel shows how these results fit together.

Rarely. The lupus classification criteria count an ANA as positive if it was positive at least once, so a later negative does not cancel an earlier positive. For people already diagnosed with lupus or juvenile idiopathic arthritis, Choosing Wisely advises against repeating a confirmed positive ANA, because the titer does not track disease activity. The results that do move with lupus activity are complement C3 and C4, which fall, and anti-dsDNA, which rises; those are the ones followed over time on an autoimmune panel.