The onset of lupus may be acute, resembling an infectious process, or it may be a progression of vague symptoms over several years.

As a result, diagnosing SLE is often a challenge. A consistent, thorough medical examination by a doctor familiar with lupus is essential to an accurate diagnosis.

This must include a complete medical history and physical examination, laboratory tests, and a period of observation (possibly years).

The doctor, nurse, or other health professional assessing a patient for lupus must keep an open mind about the varied and seemingly unrelated symptoms that the patient may describe.

For example, a careful medical history may show that sun exposure, use of certain drugs, viral disease, stress, or pregnancy aggravates symptoms, providing a vital diagnostic clue.

No single laboratory test can definitely prove or disprove SLE. Initial screening includes a complete blood count (CBC); liver and kidney screening panels; laboratory tests for specific autoantibodies (e.g., antinuclear antibodies [ANA]) such as anti-Ro, anti-La, anti-dsDNA, anti-Sm, anti-RNP, lupus anticoagulant, and anticardiolipin; an anti-phospholipid antibody test; urinalysis; blood chemistries; and erythrocyte sedimentation rate (ESR).

Abnormalities in these test results will guide further evaluations. Anti dsDNA antibody or anti-Sm antibody are autoantibodies found only in lupus. Specific immunologic studies, such as those of complement components (e.g., C3 and C4) and other autoantibodies (e.g., anti-La, anti-Ro, anti-RNP), can be helpful in diagnosis. At times, biopsies of the skin or kidney using immunofluorescent staining techniques can support a diagnosis of SLE (see Chapter 3, Laboratory Tests Used to Diagnose and Evaluate SLE, for further information).

A variety of laboratory tests, x rays, and other diagnostic tools are used to rule out other pathologic conditions and to determine the involvement of specific organs. It is important to note, however, that any single test may not be sensitive enough to reflect the intensity of the patient's symptoms or the extent of the disease's manifestations.

The American College of Rheumatology (ACR), an organization of doctors and associated health professionals who specialize in arthritis and related diseases of the bones, joints, and muscles, has developed and refined a set of classification criteria (see table below).

American College of Rheumatology Criteria for Classifying SLE for Research Purposes Malar rash Discoid rash Photosensitivity Oral ulcers Arthritis Serositis (pleuritis or pericarditis) Renal disorder (persistent proteinuria or cellular casts) Neurological disorder (seizures or psychosis) Hematologic disorder (anemia, leukopenia or lymphopenia on two or more occasions, thrombocytopenia) Immunologic disorder (abnormal anti-dsDNA or anti- Sm, positive antiphospholipid antibodies) Abnormal ANA titer Source: Tan E. The 1982 criteria for the classification of systemic lupus erythematosus (with revisions in 1997). Arthritis and Rheumatism 1982;25:1271-1277. © 1982 American College of Rheumatology. Used with permission of Lippincott-Raven Publishers.

If at least 4 of the 11 criteria develop at one time or individually over any period of observation, then the patient can be classified as an SLE patient for research purposes. However, a diagnosis of SLE can be made in a patient having fewer than four of these symptoms.

Source: National Institutes of Health, U.S.Dept of Health and Human Services