The future of RA testing…
Predicting Rheumatoid Arthritis is still impossible, but times are changing
Once upon a time, there was the Rheumatoid factor. Rheumatology could hope that the Rheumatoid factor (Rf) would be to Rheumatoid Arthritis what glucose measurement is to diabetes. But it was not so – neither for diagnosis nor for disease management. About a third of RA patients have negative Rheumatoid factor results. To my chagrin, there are still labs or rheumatologists who use the phrase “RA test” to refer to Rheumatoid factor.
But times are changing… slowly. The anti-CCP test which measures ACPA (anti-citrullinated protein/peptide antibodies) has gained in importance over the last decade is much more specific for RA (98% specificity for RA). However, many general practitioners still use an Rf or a sed rate to determine whether a rheumatology referral is warranted. The anti-CCP is said to have about 70% sensitivity for RA.
I was talking with my smart rheum doc several months ago about this problem. I asked, “I wonder how many other antibodies they will find and what they will know in a few years. The Rheumatoid factor was just the first one and the name still confuses people to think we have a definitive test.” Smart doc said, “Yes, and now they have found the MCV.” I remember reading an abstract that night which said the anti-MCV test may someday be used alternately with the anti-CCP. Scientists are doing tests to determine whether anti-MCV (anti-mutated citrullinated vimentin) better predicts Rheumatoid Arthritis diagnosis or disease severity or measures disease activity.
The future will come for predicting Rheumatoid Arthritis – eventually
Since finding anti-CCP and anti-MCV, researchers are looking for more antibodies against citrullinated proteins. Look at a study published this summer examining the synovial fluid of rheumatoid arthritis patients for other antigens that are citrullinated. Some points I read with interest:
- Besides the Rf, there are “immunoglobulins, complement factors, and other components” present in the immune complexes (IC) from the serum of RA patients. I knew it.
- “Because of the pathogenic nature of IC in RA, it is important to identify the antigens in these complexes. After identification of these antigens, a better understanding of the immunological process in the affected joints can be achieved.”
- Investigation of the immune complexes in synovial fluid could be even more informative than analyzing serum or plasma. This is a big one. What difference could this make to patients who have “normal” test results with blood serum?
- They concluded: anti-CCP positive “RA patients are more susceptible to the perpetuation of inflammation and possibly have a more severe disease state.” The data indicates that citrullinated vimentin is an important antigen in the immune complex of RA patients. This “implies its importance in the pathology of RA.”
Edit: 11 am: In just a few short years, things tend to look very different: Perhaps we have found only the tip of the proverbial iceberg with RA antigens. Take the example of the whole new science called epigenetics that has come about after the completion of the human genome project – all we assumed about gene theory and DNA (A,T,C,& G) could be altered with this one new discovery of genes being turned on and off at different times or places in the body.
- Rheumatoid Arthritis Test: Some Funny Factors
- Blood Tests for Rheumatoid Arthritis, part 2
- Rheumatoid Factor Test: Should We Rely on Rheumatoid Factor Levels?