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Lab Tests for Lupus

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Blood Tests for Lupus continued...

Anti-Ro(SSA) and Anti-La(SSB)

  • What it is: Anti-Ro(SSA) and Anti-La(SSB) are two antibodies that are commonly found together. They are specific against ribonucleic acid (RNA) proteins.
  • Why the test is used: Anti-Ro is found in anywhere from 24% to 60% of lupus patients. It's also found in 70% of people with another autoimmune disorder called Sjögren's syndrome. Anti-La is found in 35% of people with Sjögren's syndrome. For this reason, their presence may be useful in diagnosing one of these disorders. Both antibodies are associated with neonatal lupus, a rare but potentially serious problem in newborns. In pregnant women, a positive Anti-Ro(SSA) or Anti-La(SSB) warns doctors of the need to monitor the unborn baby.
  • Limitations of the test: Like other antibodies, the fact that the test is not positive in many people with lupus means it can't be used to diagnose lupus. Also, it is more indicative of Sjögren's syndrome than of lupus.

C-Reactive Protein (CRP)

  • What it is: CRP is a protein in the body that can be a marker of inflammation. 
  • Why the test is used:The test looks for inflammation, which could indicate active lupus. In some cases, the test could be used to monitor inflammation. Results of the test could indicate changes in disease activity or in response to treatment.
  • Limitations of the test: Because there are many causes for an elevated result, including infection, the test is not diagnostic for lupus. Nor can it distinguish a lupus flare from an infection. Also, the level of CRP doesn't directly correlate with lupus disease activity. So it isn't necessarily useful for monitoring disease activity.

Complement

  • 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.

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