ANA (antinuclear antibodies)

Your immune system makes antibodies against things that do not belong in your body. In autoimmunity that goes wrong and it makes antibodies against parts of your own cells. Antinuclear antibodies, ANA, are directed against parts of the cell nucleus: the DNA itself, the proteins around it and the machinery the cell uses to divide. They occur in systemic autoimmune diseases, in which the immune system affects several organs at once, such as lupus, Sjögren's syndrome, scleroderma and mixed connective tissue disease. The test places your blood on cells and looks whether antibodies stick to the nuclei. The result is therefore a word, negative or positive, and not a concentration with a unit. With a positive result the blood is diluted step by step until the staining disappears, and the last dilution at which staining was still visible is the titre: a titre of 1:80 means the blood still stained when diluted eighty times, and the higher the second number, the more antibodies there are. In addition the pattern of the staining is described, which gives a clue against which part of the nucleus the antibodies are directed. There is no band and no unit. Negative is the usual result. Which titre counts as positive is decided by the laboratory that runs the test, usually from 1:80; a low titre occurs in about one in eight healthy people, and that share rises with age and is higher in women.

ANA is the sieve at the start of the work-up of a systemic autoimmune disease. Anyone with joint pain in several joints, a rash that worsens in the sun, lasting tiredness, dry eyes and mouth, or fingers that turn white and blue in the cold gets this test as the first step. In lupus the ANA is almost always positive, so a negative result makes that diagnosis very unlikely, and that is the strongest side of the test. The second reason is that a positive ANA sets the direction of what comes next. The pattern and the titre say which follow-up tests make sense: antibodies against double-stranded DNA in lupus, against specific nuclear proteins in Sjögren, scleroderma or mixed connective tissue disease. Without the first sieve you would have to measure all of those at once. The honest limitation is that the test proves nothing on its own. About one in eight healthy people has a low titre, more often with age and in women, and an infection, some medicines and a thyroid inflammation also make the ANA positive. A positive ANA without complaints is therefore usually a finding without consequence, and the test does not belong in a panel for anyone who has no complaints; without fitting complaints it mainly produces worry.

Look first at the word and only then at the number. Negative is the usual result: the test found no antibodies against your cell nuclei, and a systemic autoimmune disease such as lupus is thereby very unlikely. A negative result does not rule out every autoimmune disease, because rheumatoid arthritis and most autoimmune thyroid and bowel diseases have their own antibodies, but for the diseases this test exists for, negative is reassuring. A positive ANA means the antibodies are there, and the question is what that is worth. In order of how often it occurs: antibodies without complaints, a low titre in someone who is otherwise healthy, which occurs in about one in eight people and usually remains a finding without consequence; your age, because the share of positive results rises with the years without there being more disease; a systemic autoimmune disease such as lupus, Sjögren or scleroderma, usually with a high titre, a specific pattern and fitting complaints; and medicines, such as some blood pressure medicines, antibiotics and medicines against heart rhythm disorders, which give a positive ANA that disappears after stopping. The higher the titre, the more likely it is more than chance. Always read ANA beside your complaints, because without complaints a positive result says little, beside the titre and the pattern, which say how strongly and against what, beside rheumatoid factor and anti-CCP if the question is about the joints, and beside CRP and ESR, which say whether an inflammation is at play.