Blood, Fluid and Tissue Tests for Arthritis

Blood and other lab tests play a critical role in diagnosing and monitoring arthritis. When your doctor needs to confirm an arthritis diagnosis, monitor disease progress, check medication effectiveness or determine if medications are causing potentially dangerous – but not evident – side effects, lab tests are ordered. 

Most tests require drawing and testing the blood, but some may involve testing urine, joint fluid or even small pieces of skin or muscle.  

Diagnosing and Monitoring Disease Activity 

If your doctor suspects you have inflammatory arthritis, these are the most common tests used to diagnose as well as monitor the disease: 

• Antinuclear antibody (ANA) – Abnormal antibodies (blood proteins) can suggest the presence of lupus, polymyositis, scleroderma, Sjogren’s syndrome, mixed connective tissue disease or rheumatoid arthritis.
• Rheumatoid factor (RF) – Detects and measures the level of an antibody that acts against the blood component gamma globulin. This test is often positive in people with rheumatoid arthritis and negative in people with psoriatic arthritis
• Anti-cyclic citrullinated peptide (anti-CCP) – Looks for the presence of an autoantibody present in about 60-80 percent of people with RA.
• Uric acid – Measures the level of uric acid in the blood helping doctors diagnose gout
• HLA tissue typing – Detects the presence of certain genetic markers to confirm a diagnosis of ankylosing spondylitis or reactive arthritis
• Erythrocyte sedimentation rate (ESR) – Measures how fast red blood cells cling together, fall and settle to help determine the presence of inflammation. 
• C-reactive protein (CRP) – Measures body-wide inflammation and may help to diagnose rheumatoid arthritis, psoriatic arthritis or lupus 
• Lyme serology – Used to determine the presence of Lyme disease.

• Skin biopsy – A small piece of skin is removed by a doctor.  It’s usually done under local anesthetic. The sample is tested in a lab and the results help determine the presence of lupus, vasculitis and psoriatic arthritis.
• Muscle biopsy – A doctor takes the tissue sample from a muscle with a biopsy needle. The sample is reviewed for signs of damage to muscle fibers to help confirm a diagnosis of polymyositis or vasculitis. 
• Joint fluid tests – A doctor removes a small amount of fluid from a joint to determine the presence of uric acid and diagnose gout.

Monitoring Medication Response and Side Effects  

Prescription and over-the-counter medications are often used to treat arthritis, so your doctor will periodically order tests to check for effectiveness and adverse side effects. These include: 

• Muscle enzyme (CPK, aldolase) – Muscles damaged by arthritis and inflammation can release enzymes into the blood.  This test measures the amount of muscle damage and how well medications reduce the inflammation.  
• Creatinine – Used to monitor kidney function in people with lupus or in those taking medications that could affect the kidneys. 
• Multibiomarker disease activity (MBDA) – Checks 12 proteins, hormones and growth factors linked to rheumatoid arthritis to determine how aggressive a person's disease is, how likely a flare may occur if medications are stopped and the drug combinations may work best  
• Liver enzyme (SGOT, SGPT, bilirubin, alkaline phosphatase) – Measures levels of liver enzymes in the blood and can help determine if there is liver damage. 
• Hematocrit (HCT) and hemoglobin (Hgb) – Measures the number and quality of red blood cells. Low counts may suggest medications are causing gastrointestinal bleeding. 
• White blood cell count – Measures the level of white blood cells. A low number may suggest that medication is decreasing the supply, hurting the body’s chances of fighting infection. 
• Platelet count – Measures the number of platelets that help the blood to clot. A low number could suggest that medication has put you at risk of bleeding heavily. 

Checking for Comorbidities 

People with arthritis are prone to developing other serious chronic diseases, or comorbidities, such as heart disease, diabetes, kidney disease and lung disease. Your doctor may regularly monitor you for these diseases and order blood and other lab tests as part of that monitoring.