Measuring Inflammation

Remember those old childhood cartoons where a guy hits his thumb with a hammer?  The thumb turns bright red, swells to three times its normal size, and hurts so much that painful rays emanate for all to see.

I remember the day I awoke in excruciating pain, my entire hand red and throbbing as if it was a model for one of those old hammer-to-thumb cartoonists.  In the cartoons, it’s funny – not so much in real life.

There have also been times my hands swelled to a lesser extent – not enough for anyone else to notice, but enough that it cut off the circulation in my ring finger.  When fingers swell so much that a perfectly sized wedding ring cuts off circulation and the finger turns blue, it’s a safe bet that there’s a fair amount of inflammation going on.

One would think that a doctor could write “significant swelling” as documentation of such events, but doctors seem to have a preference for numbers to quantify everything, including inflammation.  ESR (erythrocyte sedimentation rate) and CRP (C-Reactive Protein) are two lab tests that can be done to “measure” inflammation.  Unfortunately, those tests aren’t perfect.  People can have significant inflammation but perfectly “normal” lab results.  How ironic that someone’s feet can be too swollen to fit into shoes, hands can be too swollen to do anything, and a doctor can say, “I’m sorry, but according to your lab work, there is no inflammation.”  Many RA patients have “normal” inflammatory markers – accompanied by enough disease activity that joints are destroyed.

I’ve wondered why, if pharmaceutical companies can develop drugs to inhibit TNF-α, nobody can come up with a test to measure TNF-α in the bloodstream.  Same with interleukin-6 and the other proteins that are thought to be associated with disease activity in RA.  If numbers are so important, there should be a way to measure those things.

Scientists have been working on it, and have a new test.  This test doesn’t diagnose RA, but gives the doctor an objective number to indicate how active the RA monster is.  Announced late last year, the Vectra Disease Activity Test measures twelve proteins, applies a convoluted formula (take the logarithm of 1+CRP, multiply by .36, add the square root of this, multiply by that…) and produces a single number to quantify disease activity.

Yay!  With luck, this will be a better test.  Questions remain, though.

Given the number of RA patients with normal CRP, I don’t understand why that information is used in the new test’s calculations.  The testing company’s website compares the results to DAS28. I’d rather see some comparisons that show Vectra DA to be superior to existing tests.  What I’d really like to see is data from hundreds of RA patients with obvious disease activity but normal ESR & CRP, and see that this new test returns a high number, regardless of the normal ESR/CRP.  Show us the data.