From the Guidelines
No, a C4a (Complement Component 4a) test is not recommended to help with Lyme disease diagnosis.
Diagnostic Tests for Lyme Disease
The recommended laboratory test in the United States is a 2-tiered serologic analysis consisting of an enzyme-linked immunoassay or immunofluorescence assay, followed by reflexive immunoblotting 1.
- The sensitivity of 2-tiered testing is low (30%–40%) during early infection, but it increases to 70%–100% for disseminated Lyme disease.
- The specificity is high (>95%) during all stages of disease.
Limitations of Alternative Tests
There is no mention of C4a tests in the provided guidelines, and the use of other diagnostic tests for Lyme disease is limited 1.
- The guidelines emphasize the importance of using FDA-cleared diagnostic tests and understanding the hazards of alternative laboratory tests 1.
Clinical Diagnosis
Patients with a lesion consistent with erythema migrans and a history of exposure to Lyme-endemic areas can be diagnosed without laboratory testing 1.
- However, for all other manifestations of Lyme disease, serologic analysis is necessary to confirm the diagnosis.
Future Directions
Research is ongoing to improve the diagnosis of early Lyme disease and reduce the subjectivity of second-tier Western immunoblotting 1.
- A repository of well-characterized serum samples from patients with Lyme disease has been developed to evaluate novel diagnostic tests 1.
From the Research
C4a Test and Lyme Disease
- The C4a test can be a useful marker in patients with Lyme disease, particularly in those with chronic Lyme disease 2.
- Studies have shown that C4a levels are elevated in patients with acute Lyme disease, and this elevation can be used as an early marker of the disease 3.
- In patients with chronic Lyme disease, C4a levels have been found to be increased in those with predominant musculoskeletal symptoms, and a decrease in C4a levels has been associated with response to antibiotic therapy 2.
- The C4a test may be more useful in certain stages of Lyme disease, such as in early localized and early disseminated disease, where C-reactive protein (CRP) and serum amyloid A (SAA) levels are also elevated 4.
- It is essential to note that the diagnosis of Lyme disease is challenging and requires a combination of clinical findings, laboratory tests, and assessment of the patient's pretest probability of infection 5.
- Other laboratory tests, such as the complement fixation test, may also be useful in diagnosing Lyme disease, particularly in confirmed cases 6.