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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.

algorithmic approach to Mx of a positive ANA

clinical features suggestive of SLE
  • anti ds DNA
  • anti Sm antibody
  • if these are +ve then SLE is likely, if these are negative, SLE is unlikely
clinical features of Sjogren's
  • SS-A and SS-B antibodies
clinical features of systemic sclerosis (SS), scleroderma or myositis
  • check IF-ANA pattern:
    • centromere ⇒ limited cutaneous SSC CREST syndrome likely
    • nucleolar ⇒ SSC likely
    • other pattern ⇒ specific ENA tests
      • only RNP ⇒ MCTD
      • anti-U3 RNP ⇒ scleroderma
      • undiff. ENA (non Sm RNP, SSA, SSB) ⇒ if Jo-1 +ve ⇒ polymyositis (inflammatory myopathy)
clinical features NOT consistent with SLE or CTD
  • other causes of raised ANA:
    • drug-induced ANA
    • autoimmune liver or thyroid disease
    • chronic HCV infection
    • recent viral infection
    • elderly female
    • false positive
ana.txt · Last modified: 2012/07/12 18:33 (external edit)