Method of diagnosing Lyme disease, method of differential diagnosis of Lyme arthrisis, lysophosphatidylethanolamine to be used as a biomarker, set for diagnosing Lyme disease and set for differential diagnosis of Lyme arthrisis

The subject matter of the invention relates to a method for in vitro diagnosis of Lyme disease and a method for in vitro differential diagnosis of Lyme arthritis versus rheumatoid arthritis, in which methods, in a sample from a subject, the level of lysophosphatidylethanolamine comprising myristic acid (LysoPE(14:0)) is determined and such determined level of lysophosphatidylethanolamine is compared with the level of lysophosphatidylethanolamine comprising myristic acid in a reference sample; in wherein the level of lysophosphatidylethanolamine comprising myristic acid which is higher than the level in the said reference sample indicates that the subject suffers from Lyme disease. The subject matter of the invention further relates to lysophosphatidylethanolamine comprising myristic for use as a biomarker of Lyme disease, as a biomarker of Lyme arthritis, as a biomarker for differential diagnosis of Lyme arthritis versus rheumatoid arthritis, as a biomarker of neuroborreliosis. The subject matter of the invention also relates to a kit for in vitro diagnosis of Lyme disease and a kit for in vitro differential diagnosis of Lyme arthritis, which kits comprise a means for determining the level of lysophosphatidylethanolamine comprising myristic acid and instructions for carrying out the methods for diagnosis according to the invention.