Lyme borreliosis: tick bite, erythema migrans, disseminated forms

Infectious diseases · Symptom or situation · updated 2026-10-29

BioMG follows French guidelines. Adapt it to the guidelines and the tests available where you practise.

Frequency: 51 cases per 100 000 inhabitants per year in France in 2022 (Santé publique France, cited by the HAS) ^[1]

Tick bite or erythema migrans: no tests

No Lyme serology after a tick bite, nor for erythema migrans: the diagnosis of erythema migrans is clinical and it is treated without tests.

Detailed explanation and international comparison (in French): read it in English (machine translation)

Lyme serology after a tick bite, whatever the population ^[2].
Lyme serology in erythema migrans: poorly sensitive at this stage, a negative serology does not call the diagnosis into question ^[1].
Lyme self-tests sold in pharmacies: not recommended ^[2].

Lyme serology: ELISA, then Western blot at the laboratory's initiative if positive or equivocal (state tick exposure and clinical signs)

Repeat Lyme serology (if negative and symptoms for less than 6 weeks)if neededStrong suspicion of early disseminated disease, negative serology and symptoms present for less than 6 weeks: repeat the test 3 weeks later to look for seroconversion ^[1].

Detailed explanation and international comparison (in French): read it in English (machine translation)

Follow-up serology after treatment: no serological follow-up is recommended, cure is judged on clinical grounds and raised antibodies can persist for years ^[1].
Lyme serology in diffuse, migratory arthromyalgia without arthritis or other suggestive sign ^[1], or in an isolated psychiatric manifestation ^[1].
C6-EIA tests, microfluidic methods and any test other than serology, intrathecal synthesis, PCR and CXCL13: not recommended in routine practice ^[1].
Borrelia PCR in blood or urine: not recommended, its sensitivity there is almost nil ^[1].
Western blot straight away, without ELISA: serology starts with ELISA, Western blot is done only if ELISA is positive or equivocal ^[1,6].

FBCif neededTests proposed as non-routine by the HAS, to be chosen according to symptoms, to exclude a differential diagnosis ^[2].
CRPif neededTests proposed as non-routine by the HAS, to be chosen according to symptoms, to exclude a differential diagnosis ^[2].
Serum electrolytes, serum creatinine, liver function tests, fasting plasma glucoseif neededAccording to symptoms, to exclude a differential diagnosis ^[2].
Serum ferritinif neededAccording to symptoms (fatigue in particular) ^[2].
serum protein electrophoresisif neededAccording to symptoms (fatigue in particular) ^[2].
Creatine kinase (CK)if neededMyalgia, polyalgia or weakness: according to symptoms ^[2].
LDHif neededMyalgia, polyalgia or weakness: according to symptoms ^[2].
Serum calciumif neededMyalgia, polyalgia or weakness: according to symptoms ^[2].
Serum phosphateif neededMyalgia, polyalgia or weakness: according to symptoms ^[2].
TSHif neededThe HAS cites a “hormonal work-up” guided by symptoms, without detailing it ^[2].

Detailed explanation and international comparison (in French): read it in English (machine translation)

Repeat Lyme serology to “check cure” or explain persistent symptoms: high titres persist for years and must not lead to treatment being restarted ^[1].

Sources (6)