Lab Tests for Lupus
Blood Tests for Lupus continued...
- What it is: Complement proteins are involved in inflammation. The test can look for levels of specific complement proteins or for total complement.
- Why the test is used: Complement levels are often low in patients with active disease, especially kidney disease. So doctors may use the test to gauge or monitor disease activity.
- Limitations of the test: Like other tests, complement must be taken in the context of clinical findings and other test results. A low complement in itself is not diagnostic of lupus.
Erythrocyte Sedimentation Rate (ESR)
- What it is: ESR measures the speed of red blood cells moving toward the bottom of a test tube. When inflammation is present, blood proteins stick together and fall and collect more quickly as sediment. The more quickly the blood cells fall, the greater the inflammation.
- Why the test is used: ESR is used as a marker of inflammation. Inflammation could indicate lupus activity. This test could be used to monitor inflammation, which could indicate changes in disease activity or response to treatment.
- Limitations of the test: Like CRP, the ESR is not specific to lupus. Because there are many causes for a positive result, including infection, the test is not diagnostic for lupus. Nor can it distinguish a lupus flare from an infection. Also, the level doesn't directly correlate with lupus disease activity. So it isn't necessarily useful for monitoring disease activity.
Complete Blood Cell Count (CBC)
- What it is: CBC is a test to measure levels of different blood cells.
- Why the test is used: Abnormalities in blood cell counts, including white blood cells and red blood cells, may occur in people with lupus. This may be related to the lupus, lupus treatments, or infection. For example, leukopenia, a decrease in the number of white blood cells, is found in about 50% of people with lupus. Thrombocytopenia, or a low platelet count, occurs in about 50% of people with lupus, as well. Doctors can use this test to monitor these potentially serious problems.
- Limitations of the test: Many other medical conditions can cause abnormalities in blood cell counts. So the test by itself is not specific to a lupus diagnosis.