What Blood Tests Relate to Autoimmune Conditions?
No single blood test diagnoses an autoimmune condition. Testing usually combines broad markers, such as an ANA test, CRP or ESR and a complete blood count, with antibody tests aimed at one organ, like thyroid peroxidase antibodies for the thyroid. Which tests make sense depends on symptoms, so the choice sits with a clinician.
Why is there no single blood test for autoimmune disease?
Because there are more than 80 autoimmune diseases, and they attack different tissues. In each one the immune system makes antibodies against the body's own cells, but which antibodies, and against what, depends on the condition. Testing therefore pairs broad markers that point to immune activity or inflammation with antibody tests aimed at a specific organ.
Which broad markers are used?
| Test | What it detects | Its main limit |
|---|---|---|
| ANA (antinuclear antibody) | Antibodies against the nucleus of the body's own cells | Some healthy people test positive, and levels tend to rise with age |
| CRP | A protein the liver releases during inflammation | Rises with inflammation from any cause, including infection |
| ESR (sed rate) | How quickly red cells settle in a tube, which speeds up with inflammation | Not specific to any condition |
| Complete blood count | Red cells, white cells and platelets | Shows effects on the blood, not their cause |
ANA and ESR aren't in our price comparison. For CRP we carry the high-sensitivity version, which measures the same protein down to lower levels and is mostly ordered to assess heart risk.
Which antibody tests look at a single organ?
- Thyroid: thyroid peroxidase (TPO) antibodies. High levels are a sign of Hashimoto's disease, the most common cause of an underactive thyroid, and these antibodies can also be a sign of Graves' disease, the most common cause of an overactive one.
- Joints: rheumatoid factor (RF), used in evaluating rheumatoid arthritis.
- Small intestine: celiac disease screening, which looks for antibodies the body makes in reaction to gluten.
How do thyroid function tests fit with TPO antibodies?
They answer a different question. TSH, free T4 and free T3 show how well the thyroid is working; TPO antibodies show immune activity directed at it. The two don't have to agree, since antibodies can be present while thyroid hormone levels are still within range. That is why the antibody test and the function tests are so often ordered together.
| Test | Cheapest | Highest | Services |
|---|---|---|---|
| Complete Blood Count w/ Differential & Platelets (CBC) | $3.78 | $39.00 | 18 |
| Thyroid Peroxidase Antibodies | $4.90 | $119.00 | 17 |
| Thyroid Stimulating Hormone (TSH) | $4.92 | $59.00 | 18 |
| T4, Free | $5.52 | $89.00 | 17 |
| C-Reactive Protein, High Sensitivity | $8.32 | $69.00 | 18 |
| T3, Free | $9.83 | $99.00 | 17 |
Sources
- Autoimmune Diseases (MedlinePlus)
- ANA (Antinuclear Antibody) Test (MedlinePlus)
- Thyroid Antibodies (MedlinePlus)
- Celiac Disease Screening (MedlinePlus)
Common questions
Can a healthy person have a positive ANA test?
Yes. Some healthy people have antinuclear antibodies, levels tend to increase with age, and positive results are especially common in women over 65. A positive ANA is read alongside symptoms and other results.
What is the difference between CRP and hs-CRP?
Both measure C-reactive protein. The high-sensitivity test detects lower levels and is mostly used to assess cardiovascular risk, while a standard CRP test is used to look for inflammation.
What are thyroid peroxidase antibodies?
Antibodies directed at thyroid peroxidase, an enzyme the thyroid uses to make its hormones. High levels are a sign of Hashimoto's disease, and they can also be found in Graves' disease.
Does a high CRP mean an autoimmune condition?
No. CRP rises with inflammation from any cause, including infections and injuries, so it cannot identify an autoimmune condition by itself.