Lab Tests Used To Diagnose Lupus: Limitations & Results

0
136

Lupus is a difficult disease to diagnose, because its symptoms can be vague. And unlike some other diseases, it cannot be diagnosed with a single lab test. However, when certain clinical criteria are met, lab tests can help confirm a diagnosis of lupus. work and other tests can also help monitor the disease and show the effects of treatment.

WebMD takes a look at the uses and limitations of the tests that are commonly used to diagnose and monitor lupus.

Blood Tests for Lupus

Antinuclear Antibody (ANA)

Antiphospholipid Antibodies (APLs)

Anti-Sm

  • What it is: Anti-Sm is an antibody directed against Sm, a specific protein found in the cell nucleus.
  • Why the test is used: The protein is found in up to 30% of people with lupus. It’s rarely found in people without lupus. So a positive test can help confirm a lupus diagnosis.
  • Limitations of the test: Up to only 30% of people with lupus have a positive anti-Sm test. So relying on an anti-Sm result alone would miss a large majority of people with lupus.

Anti-dsDNA

  • What it is: Anti-dsDNA is a protein directed against double-stranded DNA. DNA is the material that makes up the body’s genetic code.
  • Why the test is used: Between 75% and 90% of people with lupus have a positive anti-dsDNA test. Also, the test is very specific for lupus. Therefore, a positive test can be useful in confirming a diagnosis. For many people, the titer, or level, of the antibodies rises as the disease becomes more active. So, doctors can also use it to help measure disease activity. Also, the presence of anti-dsDNA indicates a greater risk of , a kidney that occurs with lupus. So a positive test can alert doctors to the need to monitor the kidneys.
  • Limitations of the test: Up to 25% of people with lupus have a negative test. So, a negative test doesn’t mean a person doesn’t have lupus.

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

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

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)

Chemistry Panel

Glomerular Filtration Rate

What it is: A glomerular filtration rate measures how effective the kidneys are at filtering the blood to eliminate waste products. It can be found in a blood work report. The GFR is a calculation that includes creatinine level, age, gender, race, and weight. It shows the stage of a person’s kidney disease.

Urine Tests for Lupus

Besides blood tests used to diagnose and monitor lupus, doctors use urine tests to diagnose and monitor the effects of lupus on the kidneys. These tests include the following:

  • Urine Protein/Microalbuminuria. These tests measure the amount of protein (or albumin) in urine. Even a small amount may indicate a risk for kidney disease.
  • Creatinine Clearance: This test measures how effective the kidneys are at filtering the blood to eliminate waste products. It is conducted on urine collected over a 24-hour period.
  • Urinalysis: Urinalysis can be used in screening for kidney disease. The presence of protein, red blood cells, white blood cells, and cellular casts may all indicate kidney disease.