Thursday, January 8, 2009

C6 peptide

I have noticed a change in C6 antibody results. They are generally much lower than they were a year ago. The test measures an ELISA reaction to ViSE, a surface protein unique to Bb. The ability of the Lyme bacteria to alter this surface antigen has been well described. It is not surprising that reactivity would be variable. I would expect this to occur in individual patients; instead the change in reactivity covers a wide swath of patients, many of whom have not been treated. On the other hand, a subset of patients who have been treated extensively with antibiotics "seroconvert" with regard to this parameter. I have noted that the test measures an IgG antibody to a synthetic version of this antigen. Perhaps the test is failing because it fails to measure IgM responses which are more prominent in Lyme patients. Typically, in the past Western Blot positive Lyme patients had C6 peptide index levels, on average of 0.2 to 0.4. Recently I have seen WB positve patients with C6 indices approaching zero.


Seibertneurolyme said...

Have you questioned the lab or labs involved? Maybe the lab changed the parameters of the test or they are buying their reagents from a different supplier? Have you tried sending multiple samples to multiple labs to see if there are significant differences between labs? I think all those variables need to be ruled out if they have not been.

bill said...

I think a lot of people are finding this. The following is from a paper on the CanLyme site:

Antibodies to C(6) persisted in these patients with post-treatment Lyme disease syndrome following treatment, albeit at a markedly lower prevalence and titer than in untreated patients with acute disseminated Lyme disease. The results indicate that C(6) antibody cannot be used to assess treatment outcome or the presence of active infection in this population.

vandesu said...

I am very interested in the c6 peptide. October 2007 I was diagnosed by my Primary Care Physicial with Lyme because of a 3.07 on the c6. My Western Blot was considered negative because I only had two bands IgG 41 and IgM 39. After 4 weeks on 200 mg of doxy I asked my PCP to retest me. My c6 doubled to 6.47 and the same two Western Blot bands appeard. My PCP sent me to the Infectious disease specialist at our local hospital who said that the only explanation for the increased c6 without a positive Western Blot was most likely due to a weird cross reaction. He said I may or may not have had Lyme, but it was gone now! Luckily, after a major relapse a friend suggested I see a LLMD and with his expertise and treatment I have made progress ( not as much progress as I would like but my severe neurological symptoms have improved). My LLMD does not discuss retesting but I have had it in my mind that I would like to see if the c6 has changed after 8 months of antibiotic treatment. This posting seems to indicate that it would not be useful as an indicator of progress. Am I interpreting this correctly?

Another question - I have become worried about my daughter having Lyme and had her tested by a local doctor. Her c6 came back as .70 so it was considered negative. She only had IgG and IgM 41 on the western blot so the current evaluation is that does not have Lyme. We are having the Western Blot repeated by Igenex. Based upon my past reading of posts about the c6 I get the impression that .70 could be a signficant level for Lyme (the reference range from the lab said it must be greater than .91). Am I correct about this? From your posting it sounds like there are Lyme patients with lower c6 results who are definitely Lyme positive.

Lyme MD - thank you for this blog. I find it one of the most helpful resources available as I deal with this disease. In my eyes the time and commitment you put into this is nothing short of extraordinary. I wish there were more doctors like you in our world.

lymie said...

Several labs are known to have changed the cutoff value on various tests with the apparent reason of reducing the number of positive results.

Could this be the case with the C6 test? In other words, done something to reduce the level?

Is this just one lab, or more than one?

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