When Lab Tests Lie | Rheumatoid Arthritis

Twelve years ago, I met R.T., a 35-year-old female patient who had previously been diagnosed with rheumatoid arthritis. Her rheumatoid factor was positive at 49. Her sedimentation rate and C-reactive protein were also elevated. Her joints were visibly swollen and tender on exam. Everything was indicative of significant disease activity.

After discussing treatment options, we decided to start R.T. on a titration dose of methotrexate, 3 pills (7.5 mg) a week on the first Friday and increasing by one pill every Friday until she reached a goal of 17.5 per week. One month later, her liver enzymes were 3 times the upper limits of normal on her laboratory panel, or roughly 130. I called R.T. immediately and had her come in for an evaluation.

In my head, I began running through possible explanations. Did she have a drinking problem that she was covering up? Had she failed to tell me about other medications she was taking such as acetaminophen?

When R.T. next came in, I began by asking if she had any stressors at home. “Yes, my husband is very sick with hepatitis C,” she told me.

I took a second or two to collect myself and then asked R.T. if she had ever been tested for hepatitis C. She told me, “No,” and so I asked if I could run a hepatitis panel and viral load if the panel was positive. She reluctantly agreed.

Her viral load came back showing more than a million copies of the virus. It was then clear that the patient’s high rheumatoid factor level and other elevated test results were due to her active hepatitis C and that her joint pain was a manifestation of her viral disease and not due to rheumatoid arthritis. I referred R.T. to an infectious disease specialist after apologizing for misdiagnosing her.

The Centers for Disease Control and Prevention recommends testing all patients between the ages of 13-64 for HIV infections, and testing all individuals born between 1945-64 for hepatitis C.1 According to the package inserts for current biologics used to treat RA, hepatitis B screening should be performed prior to the initiation of those medications in all patients.

While it is impossible to overestimate the importance of a complete physical exam—including a formal joint count—a case like this shows how lab results can be misinterpreted if we don’t ask patients the right questions.

AUTHOR PROFILE: Iris Zink, MSN, NP, is a nurse practitioner at the Beals Institute in Lansing, Michigan, and the President of the Rheumatology Nurses Society.




  1. Centers for Disease Control and Prevention. Screening Recommendations Referenced in the 2015 STD Treatment Guidelines and Original Recommendation Sources. Available at www.cdc.gov/std/tg2015/screening-recs-2015-std-tx-guidelines.pdf. Accessed July 8, 2015.