Serological test results for Lyme disease should be interpreted as follows: a positive or equivocal ELISA test should be followed by an immunoblot test for confirmation, and treatment may be started while awaiting results if there is high clinical suspicion NICE NG95.
If the ELISA is negative but symptoms persist, review the patient's history and consider alternative diagnoses; if Lyme disease is still suspected within 4 weeks of symptom onset, repeat the ELISA after 4–6 weeks, or perform an immunoblot test if symptoms have lasted 12 weeks or more NICE NG95.
A positive immunoblot test confirms Lyme disease, and treatment with antibiotics should be initiated NICE NG95.
If the immunoblot is negative, regardless of ELISA results, but symptoms persist, consider referral to a specialist for further assessment, additional testing (such as synovial fluid analysis or lumbar puncture), or to explore alternative diagnoses NICE NG95.
If the immunoblot is negative and symptoms have resolved, no treatment is required NICE NG95.
Referral to a specialist should also be considered in cases with focal symptoms or neurological, cardiac, or dermatological features, or if there is diagnostic uncertainty NICE NG95.