The testing of the antinuclear antibody titer, or ANA titer for short, is one of the most reliable diagnostic tests for lupus. 95% of patients with lupus are positive for the ANA titer. However, lower titers of this test can also be found in elderly patients or some patients with other autoimmune disorders.
As mentioned in the introduction there is a cross connection between six autoimmune diseases, probably because they all involve autoimmune antibodies (the other ones are rheumatoid arthritis, scleroderma, polymyositis, Sjögren’s syndrome and dermatomyositis).
Each of these has its own symptom expression. With a flare-up of lupus the sedimentation rate (ESR or erythrocyte sedimentation rate) is elevated and remains so for quite some time, even when the flare-up is abating. As infections can also have an increased ESR, other tests are needed to distinguish between lupus and infection.
One such test is the C-reactive protein, which usually stays normal in a lupus flare, but is elevated in infection (Ref. 1, p. 61). Other blood tests show a low white blood cell count (“leukopenia”) and anemia. The anemia can be nonspecific or hemolytic. Low platelet counts less than 100,000 per microliter is also common with lupus.
The ANA titer usually tends to increase with a lupus flare and then get lower again when the flare is over. A more specialized test, antibodies to double stranded DNA, can be found in less than 50% of lupus patients.
But if this is rising while C3 and C4 complement in the blood is falling with repeat tests, it may indicate that lupus is now affecting the kidneys (Ref. 1, p.62). Another subset of lupus patients who develop blood clots (thromboembolic complications) or fetal loss (in pregnant patients) have antiphospholipid antibodies such as anticardiolipin antibodies in their blood tests. There are more specific antibodies to soluble cellular antigens that the rheumatologist may utilize to categorize more subsets among lupus patients (Ref. 1, p.62).
References:
1. ABC of rheumatology, second edition, edited by Michael L. Snaith , M.D., BMJ Books, 1999. Chapter 15.
2. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 50.
3. BP Tsao et al. Curr Rheumatol Rep 2001 Jun;3(3):183-190.
4. D Alarcon-Segovia Isr Med Assoc J 2001 Feb;3(2):127-130.
5. CC Mok Semin Arthritis Rheum 2001 Jun;30(6):426-435.
6. Goldman: Cecil Textbook of Medicine, 21st ed.(©2000)W.B.Saunders
7. Ferri: Ferri’s Clinical Advisor: Instant Diagnosis and Treatment, 2004 ed., Copyright © 2004 Mosby, Inc.
8. Rakel: Conn’s Current Therapy 2004, 56th ed., Copyright © 2004 Elsevier
