Systemic Lupus Erythematosus - Diagnosis

As with the ANA, these antibodies also have a tendency to appear and disappear in a single patient. Patients who have these autoantibodies as well as blood clotting problems or frequent miscarriage are diagnosed with antiphospholipid syndrome (APS), which often occurs in SLE but can also develop independently.

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Miscellaneous Blood Tests

Complement. Blood tests of patients with SLE often show low levels of serum complement, a protein in the blood that aids the body's infection fighters. Individual proteins are termed by the letter "C" followed by a number; common complement tests measure C3, C4, C1q, and CH50. There is some evidence that complete deficiencies of C1q may be a key factor in the inability of the immune system to contain the autoimmunity process. Complement levels are especially low if there is kidney involvement or other disease activity.

LE Cell Tests. The first blood test ever used for SLE called LE (lupus erythematosus) cell test is positive in only about half of patients with SLE and is no longer used that often.

Blood Count. White and red blood cell and platelet counts are usually lower than normal and, depending on severity, are used to determine complications, such as anemia or infection.

Click the icon to see an image of the formed elements of blood.

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.

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.