Blood Tests to Diagnose Arthritis
Your doctor will use several blood tests to help diagnose you with rheumatoid arthritis (RA) and other inflammatory conditions.
Blood tests are usually fast. The doctor sends you to a lab where a worker puts a needle into one of your veins. They take, or "draw," blood into several test tubes. The tests take a few days, and the doctor will call you to go over the results. Common blood tests for rheumatoid arthritis include:
Rheumatoid factor (RF)
What it measures: Rheumatoid factor is a group of proteins your body makes when your immune system attacks healthy tissue.
What’s normal: 0-20 u/mL (units per milliliter of blood)
What’s high: 20 u/mL or higher
What it means: About 70% to 90% of people with a high reading have RA. But people without RA can still have rheumatoid factor. In general, if you have RA but don’t have high RF, your disease will be less severe. RF levels may stay high even if you go into remission.
Other conditions you might have include:
- A long-term infection
- Bacterial endocarditis
- Cancer
- Diabetes
- Lupus
- Dermatomyositis
- Infectious mononucleosis
- Leukemia
- Scleroderma
- Sjögren’s syndrome
Learn more about the rheumatoid factor test.
Anti-cyclic citrullinated peptide (anti-CCP)
What it measures: Proteins your body makes when there is inflammation. You’ll probably have it done along with the RF test.
What’s normal: 20 u/mL or less
What it means: This test offers a way to catch RA in its early stages. Levels are high in people who have RA or those who are about to get it. A positive test means there’s a 97% chance you have RA. If you have anti-CCP antibodies, your rheumatoid arthritis might be more severe.
Other conditions you might have: None. This test is used only to look for RA.
Erythrocyte sedimentation rate (ESR)
What it measures: The speed at which your red blood cells clump and fall together to the bottom of a glass tube within an hour. Your doctor might call it a sed rate.
What’s normal:
- Men younger than 50: 0-15 mm/h (millimeters per hour)
- Men older than 50: 0-20 mm/h
- Women younger than 50: 0-20 mm/h
- Women older than 50: 0-30 mm/h
What it means: In healthy people, the ESR is low. Inflammation makes cells heavier, so they fall faster. Higher levels tend to happen along with active disease, though not exactly.
Other conditions you might have: A high ESR rate doesn't point to any particular disease, but it's a general sign of how much inflammation is in your body. It could be tied to disease activity if you have:
- Polymyalgia rheumatica
- Systemic vasculitis
- Temporal arteritis
Get more information on the erythrocyte sedimentation rate test.
C-reactive protein (CRP)
What it measures: A protein your liver makes when inflammation is present
What’s normal: Generally, less than 10 milligrams per liter, but results vary from person to person and from lab to lab
What it means: CRP levels often go up before you have symptoms, so this test helps doctors find the disease early. A high level suggests significant inflammation or injury in your body. Doctors also use this test after you’re diagnosed to monitor disease activity and to understand how well your treatment is working.
Other conditions you might have:
- Autoimmune disease
- Heart attack
- Infection
Find out more on the C-reactive protein test.
Antinuclear antibody (ANA)
What it measures: This series of tests measures the presence of certain unusual antibodies in your blood.
What’s normal: These tests are measured in titer, a ratio for the lowest mix of a solution and a substance at which a reaction takes place. A value of 1:40 dilution (or 1 part antibodies to 40 parts solution) is negative.
If the ANA is positive, you may have an autoimmune disorder, but the test alone can't make a reliable diagnosis. If the ANA is negative, it is likely that you don't have one.
Other conditions you might have: The profile helps your doctor look for diseases such as:
- Lupus
- Scleroderma
- Sjögren's syndrome
Learn more about antinuclear antibody testing.
HLA-B27
What it measures: A protein on the surface of white blood cells
It is not an abnormal finding: 8%-10% of white people may have it, though most do not have a disease.
What it means: HLA-B27 is a gene that’s linked to a group of conditions (you might hear it called a genetic marker) known as spondyloarthropathies. They involve joints and the places where ligaments and tendons attach to your bones.
Other conditions you might have:
- Ankylosing spondylitis
- Juvenile arthritis
- Psoriatic arthritis
- Reiter's syndrome (reactive arthritis)
Complete blood count
What it measures:
- Red blood cells, which carry oxygen from your lungs to your body
- White blood cells, which fight infection
- Hematocrit, a measurement of how much red blood is in your system
- Hemoglobin, a protein that helps your blood carry oxygen
- Platelets, which help your blood clot
What’s normal:
- Red blood cells: 3.93 to 5.69 million per cubic millimeter (million/mm3)
- White blood cells: 4.5 to 11.1 thousand per cubic millimeter (thousand/mm3)
- Hematocrit:
- Men: 36% to 52%
- Women: 34% to 46%
- Hemoglobin:
- Men: 13.2 to 17.3 grams per deciliter (g/dL)
- Women: 11.7 to 16.1 g/dL
- Platelets: 150 to 450 thousand/mm3
What it means: It helps your doctor decide if your treatments or the disease itself is causing other problems, like anemia. It also checks for side effects caused by some medications.
Other conditions you might have:
- Anemia (various types)
- Infections
- Leukemia
Find out more about complete blood count testing.
Creatine kinase (CK)
What it measures: Levels of the muscle enzyme creatine phosphokinase (CPK)
What’s normal: Levels vary by age, gender, and race. Your doctor will tell you what your results mean.
What it means: You might have an inflammatory muscle disease. Higher levels of CPK can also show up after trauma, injections into a muscle, muscle disease due to an underactive thyroid, and while taking certain medications such as cholesterol-lowering drugs called statins.
Other conditions you might have:
- Lupus
- Heart attack
- Muscular dystrophy
- Early pregnancy
Complement
What it measures: More than 30 blood proteins that work together in your immune system during an inflammatory response. Complement proteins can get used up during this process.
What’s normal:
- Serum CH50: 30-75 u/mL (units per milliliter)
- Serum C3:
- Men: 88-252 mg/dL (milligrams per deciliter)
- Women: 88-206 mg/dL
- Serum C4:
- Men: 12-72 mg/dL
- Women: 13-75 mg/dL
What it means: Lower levels of all three components may signal lupus and vasculitis, or inflamed blood vessels. If you have lupus with kidney disease, your doctor may continue to give you this test because levels rise and fall along with disease activity.
Other conditions you might have:
- Infection
- Kidney disease
- Liver disease
Cryoglobulins
What it measures: Proteins that clump together when they’re exposed to cold and dissolve when they’re warm
What it means: There are three types of cryoglobulins:
- Type I is more common in cancer.
- Type II is usually seen with hepatitis C or viral infections.
- Type III is more likely to mean an autoimmune disease.
What’s normal: A negative result. There are no cryoglobulins in your blood.
Other conditions you might have:
- Hepatitis B and hepatitis C
- HIV
- Kidney disease
- Lyme disease
- Lupus
- Multiple myeloma
- Sjögren's syndrome
Testing for Other Autoimmune Conditions
Antineutrophil cytoplasmic antibodies (ANCA)
What it measures: Proteins that attack white blood cells
What’s normal: A negative result (no antibodies in your blood), or a titer of less than 1:20
What it means: You have a form of vasculitis, or inflamed blood vessels. You may get this test after you’re diagnosed, too. It helps your doctor see how your disease is progressing, though the link to disease activity isn’t perfect.
Other conditions you might have:
- Granulomatosis with polyangiitis
- Microscopic polyangiitis
- Churg-Strauss syndrome
