Clearing Up Confusion About C-Reactive Protein Numbers
Dear Dr. Roach: I am a healthy 57-year-old woman, relatively fit and active. Ten years ago, during a routine wellness exam, my bloodwork indicated an elevated CRP of 10. In the next decade, it has gradually increased and seems to dance around 15 or 16, though it has been as high as 26.
Concerned about the numbers, my primary care doctor referred me to a rheumatologist, who diagnosed me with mild spondyloarthropy and sacroiliitis. He wanted to put me on a disease-modifying drug, but when I read about the side effects, I would say I have basic age-appropriate pain/stiffness that is managed with regular exercise and an occasional Aleve for flare-ups, so I decided not to try any other drugs to bring down the lab number. When I said to the doc, “But I don’t have a disease,” his response was, but you will.” I also passed a stress test with flying colors, so I don’t think it is a cardiac issue.
My primary doctor and rheumatologist have both told me it is truly just a mystery and that I can wait until something manifests (unless I want to go on the heavy-duty disease-modifying drug recommended by the rheumatologist).
At one time, my primary doctor recommended a low-dose statin (my cholesterol is normal range), but the CRP increased after six months, so I stopped that. — S.S.
Dear Dr. Roach: I am a professor emeritus of Medicine at Case Western Reserve University, and have studied C-reactive protein for many years. I am troubled by a recent column. Your correspondent told you that his “cardiac CRP was 3.9.” This is a term often used to refer to CRP level usually reported as mg/L.) It is very important to note that there is no uniformity in the units that are used to report CRP levels. Some laboratories report CRP concentrations as mg/dL while others employ mg/L.
You responded with a reasoned, brief discussion of arthritis and CRP. However, you concluded by stating “Your CRP is much higher than I would expect from osteoarthritis.” In fact, concentrations in this range are highly prevalent, occurring in about 30 percent of the American population, and seem to reflect some degree of metabolic stress. Many relatively benign conditions are associated with levels in this range. If the units had been mg/dL, then it would indeed have truly been elevated. — Irving Kushner, M.D.
Answer: I took Dr. Kushner’s advice and checked the CRP units for SS, which were indeed mg/L. Levels of 15-26 are not minor elevations, and are more likely to represent an inflammatory condition, such as the underlying cause of the sacroiliitis seen on your X-ray. Several conditions can cause sacroiliitis, such as ankylosing spondylitis, rheumatoid arthritis, reactive arthritis (formerly called Reiter’s syndrome) and arthritis due to inflammatory bowel disease.
We are taught in medicine not to treat a number. The high CRP is a clue to an underlying condition, as is the X-ray, but I would think twice before using a disease-modifying drug (like methotrexate) in absence of symptoms. Treatment for these serious rheumatic diseases is based on careful assessment of symptoms, exam, labs and imaging. The rheumatologist needs to consider where you are now, as well as prevent problems in the future.
I would not recommend a statin based on the CRP in your case.
Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.c ornell.edu or write to P.O. Box 536475, Orlando, FL 32853-6475.