Wednesday, July 9, 2014

Lyme Disease Tests: How reliable is the C6 ELISA?

What's in your wallet?   

It's a catchy line from Capital One's popular advertising campaign.  But, instead of inquiring about his wallet, you may seriously want to ask your doctor,

"What's in your laboratory's 

Lyme disease test kit?"

                                  - NIH

Recent news articles have described the C6 ELISA as a preferable Lyme disease test.  It's still recommended by some at the IDSA as a possible one-step test to detect Lyme disease in humans. It's suggested by others as a "sensitive" screening tool, to be ordered prior to a western blot. In addition, a C6 SNAP test is used by many veterinarians to test dogs and other animals for Lyme Borreliosis.  But, is the C6 actually reliable? 

After reviewing the published literature, GALDA gives the C6 a big...


Why?  Just keep reading...

In 2011, the National Institutes of Health's Dr. Peter Burbelo and his colleagues wrote:

Recently, the C6 SNAP test has been used for the serological diagnosis of equine Lyme disease.  Unfortunately, Chang and colleagues found that the C6 SNAP test detected only 63% of known, experimentally B. burgdorferi-infected horses, suggesting that this test is suboptimal for the diagnosis of equine infection. In light of the poor sensitivity of the currently available C6 SNAP test, a better understanding of humoral responses in B. burgdorferi-infected horses is needed.(1)

A previous study using the SNAP C6 test with experimental animals showed 65% sensitivity in detecting B. burgdorferi-infected horses and ponies and matched quite well with our C6-based VOVO test showing 72% sensitivity. (1)

Another study revealing the insensitivity of the C6 was published in 2012.  Lyme-infected monkeys with confirmed evidence of persistent infection were tested over time using the C6 ELISA.  The test missed the disease in 50% of the animals. (2)   

Worse still, this is nothing new. Dr. Ed Masters explored using the C6 ELISA years ago to test his human Missouri Lyme disease patients.  The C6 only detected 7/91 cases, with an additional 6 that were "probable positives." 

78/91 tested below 1 SD (negative) suggesting the agent or agents of Masters' Disease (Lyme disease transmitted by lone star ticks) may not express C6 epitopes. (3)

Other studies describe the unreliability of the C6 ELISA, as well.

Okay, let's think this through:  

- Positive cases of Lyme disease detected in dogs using the SNAP C6 ELISA are reported on the IDEXX "Dogs and" website.  There are some cases but not a huge percentage reported from the southern USA. 

- Chang's work showed that the C6 missed 37% of the horses infected, Embers' work showed the C6 missed 50% of monkeys with persistent infection.  And this was in trying to detect one Lyme bacterial species, Borrelia burgdorferi sensu stricto (Bbss). But the C6 is still used quite often in vets' offices to test dogs.

- In the southern USA,  there are several other Lyme Borrelia species and strains, not only Bbss, and these may express different determinants that the C6 ELISA doesn't pick up (as suggested by Masters' research).  Some of the other Lyme Borrelia species found here, including Borrelia bissettii, Borrelia andersonii and Borrelia americana, have been identified in symptomatic patients in recent years. 

- The C6 only detected 7 out of 91 (8%) Missouri Lyme disease cases - cases most likely vectored by the lone star tick since "deer ticks" were said to be rare to nonexistent in Missouri at that time.  As Dr. Ed Masters noted in another paper, the whole cell sonicated ELISA detected the greatest number of Lyme cases among his patients, though it was still far from foolproof.

What does it all mean?

So, do the reported cases on the map only represent about 8% of the southern dogs actually infected with various forms of Lyme Borreliosis?   How many dogs in the southern USA - where the aggressive lone star tick is so prevalent - are truly infected with some undetected strain(s) of Lyme Borrelia?

Most importantly, what about people infected with other Lyme Borrelia species and strains that the C6 and other Lyme disease tests are not designed to detect?

Buyer beware: there is still no test that can rule out Lyme disease. While the test might be useful sometimes, negative results obtained by using the C6 ELISA cannot be trusted. This may be particularly true in areas where the lone star tick is prevalent and/or so many other species and strains of Lyme Borrelia are known to exist.

So, really...ask your doctors...What's in your laboratory's Lyme disease test  kit?  Is it a C6 ELISA, a FLA-based ELISA, a whole cell sonicated ELISA?  Do you know what studies show about the sensitivity of each one?  And what do they show about the reliability of western blots and PCR used in testing for Lyme disease?  Because, all of this should matter to doctors who truly care about their patients, especially when so many people may be suffering from an undiagnosed, treatable bacterial infection.


1.  Burbelo, P., et al. 2011. Antibody Profiling of Borrelia burgdorferi Infection in Horses.  Clin Vaccine Immunol. 18(9): 1562–1567.

2.  Embers, M., et al.  2012.  Persistence of Borrelia burgdorferi in Rhesus Macaques following Antibiotic Treatment of Disseminated Infection.  PLoS ONE 7(1): e29914.

3. Masters, E and Phillip, M.  C6 Lyme Peptide ELISA Serosurvey of Missouri Patients.  Supplement, Lyme Disease Resource Center, Page 23.

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