CDC Two-Tier Lyme Serology Algorithm
Reads Lyme disease serology through the CDC two-tier algorithm and says what the pair of results means.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Days since symptom onset
- 60
- First tier
- Positive
- Second tier
- IgM reactive, IgG not reactive
Result: negative by the algorithm: IgM only, outside the 30 day window, at 60 days
The tool opens with these values already filled in. Replace them with your own.
What the result means
- First tier
- An enzyme immunoassay or immunofluorescence assay. Negative ends the testing. Positive or equivocal calls for a second tier.
- Second tier
- An IgM and IgG immunoblot, or under the 2019 modified algorithm a second, different enzyme immunoassay. It is an equal alternative, not a lesser test.
- Positive
- A reactive first tier with a reactive IgG second tier, or with an IgM-only second tier inside thirty days of symptom onset.
- IgM beyond 30 days
- IgM reactivity without IgG beyond thirty days from symptom onset is a false positive and does not support the diagnosis.
- Erythema migrans
- A clinical diagnosis, treated on sight without serology. Antibodies take weeks to appear, so a test drawn at the rash is frequently negative.
- Treatment response
- Serology does not measure it. Antibodies persist for years after successful treatment, so a repeat titer answers nothing about cure.
What you enter
- Erythema migrans is present (a clinical diagnosis; serology is not indicated)
- Days since symptom onset (an IgM-only second tier counts only within 30)
- First tier: enzyme immunoassay or immunofluorescence assay
- Second tier: immunoblot, or a second enzyme immunoassay
How this is calculated
Mead P, Petersen J, Hinckley A. Updated CDC Recommendation for Serologic Diagnosis of Lyme Disease. MMWR Morb Mortal Wkly Rep. 2019;68(32):703. Second National Conference recommendations, MMWR 1995;44(31):590-591. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.