anti-nuclear antibodies (ANA)

introduction

Antinuclear antibodies (ANAs) are diverse, and some have specific disease associations. Many of the autoimmune diseases are associated with a positive ANA test. A positive ANA is 1 of the 11 criteria used in the diagnosis SLE.
This is a useful screening test if SLE is suspected because a negative test virtually rules out SLE. Results are reported as a titre with a pattern.
The ANA test is positive in 98% of patients with systemic lupus erythematosus (SLE), 40%-70% of those with other connective tissue diseases, up to 20% with autoimmune thyroid and liver disease and in 3-5% of healthy adults (at a cutoff titre of 1:160).
IF-ANA may be +ve in 3-5% of healthy adults (ie. false positive), and may be negative in mild or remission phases (false negatives)
An ANA should be ordered when a connective tissue disease such as SLE is suspected on the basis of several specific findings on history or physical examination. These findings could include photosensitivity, malar rash, alopecia, mouth ulcers, sicca symptoms, Raynaud's phenomenon, inflammatory arthritis or pleuropericarditis. systemic lupus erythematosus (SLE) can usually be ruled out if the test is negative. However, a positive test does not by itself ensure a diagnosis of a connective tissue disease. The ANA is valueless in monitoring disease activity and, thus, does not need to be repeated.

speckled pattern may be normal, especially in those aged over 60yrs, if anti-ENA is negative
a low titre 1:40, 1:80, 1:160 often suggests there is no auto-immune disease as normal people without auto-immune disease have a relatively high probability of a result in this range ¹⁾
a medium titre 1:320 is less clear and needs further context to interpret
a high titre 1:640, 1:1280 or 1:2560 generally indicates more severe auto-immune disease

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