Laboratory Abnormalities

There are no specific tests for lupus. The lupus erythematosus cell, formed when complexes of nuclei and antibodies are phagocytosed by PMNs, is highly specific but of low sensitivity. ANA, anti-double-stranded DNA, and antiphospholipid antibody are all markers for SLE, but antibody test results are misleading if not considered in the clinical context. From 2% to 5% of patients with SLE are ANA negative, whereas 5% of the normal population and up to 20% of healthy young women are ANA positive (Fritzler et al., 1985). Antibodies to an RNA-protein complex called Sm (anti-Smith antibody) and to double-stranded DNA (dsDNA) are almost unique for SLE, both being 95% specific. ESR is normally increased, whereas CRP is normal (Linares et al., 1986).

Autoantibodies in SLE include ANA and anticytoplas-mic antibodies (including lipoproteins), antibodies against blood cells, antibodies against various organs and structures (e.g., gastric mucosa, neurons, muscle sarcolemma, thyro-globulin), and antibodies against collagen. Different antibodies against different parts of the cell nucleus appear as the four patterns of ANA staining. These include membranous antibodies against single-stranded DNA, speckled antibodies against extractable ribonucleoproteins, dsDNA antibodies against native dsDNA, nucleolar antibodies against nucleo-lar antigens and sometimes associated with scleroderma, and homogeneous antibodies against deoxyribonucleoproteins.

In active SLE, serum complement (C3, C4, and often CH50) levels are depressed. ESR is often elevated during active disease but is not a precise indicator of disease activity. DNA autoantibodies also do not correlate well with periods of active disease. A normochromic normocytic anemia, leu-kopenia (2500-4000 WBCs/mm3), and thrombocytopenia are common because of bone marrow suppression or the autoimmune process, although other causes must be ruled out first. SLE can manifest as immune thrombocytic purpura years before the patient develops other symptoms of lupus.

The confirming tests for lupus (e.g., ANA, anti-DNA titers) are generally not helpful in follow-up. Monitoring for disease or treatment sequelae often involves serial CBC, renal function testing (creatinine), urinalysis, C3 and C4, and laboratory tests monitoring specific drug toxicities, including homocysteine and cholesterol levels for patients taking corticosteroids.

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