Systemic Lupus Erythematosus - Diagnosis

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Skin Tests

If a skin rash is present, the doctor may take a biopsy (a tissue sample) from the margin of a skin lesion. A test known as a lupus band detects antibodies known as immunoglobulin G (IgG), which are located just below the outer layer of the tissue sample. They are present in about 80% of patients with active SLE and in between 30 - 40% of those with inactive disease. The biopsy will not differentiate between systemic and discoid lupus, but it can rule out other diseases. Tests for other antibodies will rule out or confirm discoid lupus and subacute cutaneous lupus.

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Tests for Serious Complications of SLE

Kidney Damage and Lupus Nephritis. Kidney damage in patients already diagnosed with SLE may be detected from the following tests:

• Blood tests that measure creatinine, a protein metabolized in muscles and excreted in the urine. High levels suggest kidney damage, although it can also be present with normal creative levels.
• Tests for detecting anti-ds DNA antibodies and complement. High levels of anti-ds DNA and low levels of complement C3 suggest kidney damage. (It should be noted, however, that some patients with severe kidney damage show low levels of anti-ds DNA.) Testing for anti-C1q antibodies now appears to be an even more reliable indicator of lupus nephritis.
• Urine analyses. They should be performed at 4- to 6-month intervals to check for signs of kidney involvement.
• A kidney biopsy. This may be performed to determine if lupus nephritis is present when less invasive tests indicate kidney involvement. It is not absolutely accurate but it helps determine treatment. Electron microscopy (very high-powered electronic microscopes) may be especially important in obtaining critical information on the degree of kidney damage.

Lung and Heart Involvement. A chest x-ray may be performed to check lung and heart function. An electrocardiogram and an echocardiogram are administered if heart disease is suspected.