**5.1 Laboratory and microbiology test**

 There are no specific analytical tests that suggest the presence of an NBTE. Depending on the causative disease, we can find analytical alterations that support or not a diagnosis. A complete blood test should be performed, including blood count, biochemistry, liver test, and coagulation panel. In some patients with NBTE, data of disseminated intravascular coagulation can be evidenced. In case of suspicion of autoimmune disease, a complete immunological study should be requested, mainly from SLE and APS (including antinuclear antibody, anti-doublestranded DNA, and antiphospholipid antibodies). It will be necessary to carry out a screening of the most frequent types of neoplasms taking into account the sex, the comorbidities, and the age range of the patient.

 Many authors suggest that before diagnosing an NBTE, it is essential to rule out an IE after carrying out different microbiological tests. In fact, at least three sets of blood cultures must be made before any suspicion of IE. Sometimes blood cultures in the presence of valvular vegetations can be persistently negative and do not rule out the presence of IE (called "culture-negative endocarditis"). For this reason, cultures of other biological fluids (urine, feces, etc.) should be performed, and serology and PCR should be performed on those less frequent or "atypical" microorganisms that can also cause IE (e.g., *Brucella* spp., *Coxiella burnetii*, *Legionella*, etc.) (**Table 2**).
