Heparin induced thrombocytopenia (HIT) is an immune-mediated disorder due to antibodies anti platelet factor 4-heparin (HPIA). Thrombocytopenia is often moderate but certain patients can develop morbid thrombotic complications. HPIA detection by ELISA has high sensitivity but low specificity, and low titers (without clinical significance) are frequent. A pretest clinical score (4T's) was developed in order to recognize patients that are at high risk of HIT. The aim of this study was to correlate HPIA levels and the 4T's score of consecutive patients derived to our center. We evaluated 84 patients (35 of them developed thrombosis); the clinical questionnaire was sent along with the sample and was analyzed by an investigator who did not know the patients' characteristics, and 4T's scores were calculated before performing the laboratory tests. HPIA were measured by ELISA (Asserachrom HPIA) that detects IgG, IgM and IgA isotypes, (the only reagent available in our country). 4T's score correlated with HPIA levels (rho spearman 0.472, p < 0.001). Patients with 4T's = 6 had higher absorbance percentages than those with = 5 (67 vs. 39%, p < 0.001), and patients with thrombosis also presented higher titers (59 vs. 39%, p = 0.017) than those who did not develop this complication. In conclusion, high titers of HPIA measured by EIA which detects the 3 isotypes, clearly correlate with 4T's score = 6 and are more frequent in patients who develop thrombosis, just as reported when an IgG specific ELISA is used.