Background and importance Heparin-induced thrombocytopenia (HIT) is a rare but serious complication caused by antibodies to the heparin/platelet factor 4 complex. It produces sudden thrombocytopenia (decrease of more than 50% of the platelet count) during the first days of treatment with thrombosis. Once the diagnosis is suspected/confirmed by antigenic methods, heparin should be discontinued and replaced with alternative anticoagulants. Fondaparinux is frequently used as ‘off label’.

Aim and objectives To analyse the relationship between fondaparinux and platelet recovery when it is used in suspected HIT, as well as the correct diagnosis of this pathology coinciding with the COVID-19 pandemic, a disease that also frequently produces thrombocytopenia, in a tertiary hospital.

Material and methods Cross-sectional descriptive observational study. All patients who started treatment with fondaparinux during 4 months were collected, coinciding with a high number of admissions due to COVID-19. The variables collected were: sex, age, platelet count at the start of heparin or derivatives, at the beginning and end of treatment with fondaparinux, days of treatment with heparin and fondaparinux, request for antigenic tests to confirm HIT, and diagnosis of COVID-19

Results 40 patients (31 men, 77.5%) were included. The mean age was 71.5 (32–98) years. The mean platelet count at baseline was 136*10³/μL, when heparin was discontinued and fondaparinux was initiated it was 87*10³/μL and when fondaparinux was discontinued 151*10³/μL. The median number of days with heparin was 6 (0–58), with fondaparinux 6.5 (1–41). 57.5% (n=23) of the patients were diagnosed with COVID-19. Tests for diagnosis of HIT were requested in only 10% of cases (n=4), being confirmed in 1 patient.

Conclusion and relevance In our case series, there was a high number of suspected HIT. Although after treatment with fondaparinux, the platelet count recovers, this is probably due in most cases to other reasons, such as COVID-19 infection, coinciding with the recovery of the problem that causes it rather than to treatment with fondaparinux. Following the low proportion of requests for antigenic tests to confirm HIT, we consider it vitally important to promote these tests, which would avoid overdiagnosis in most patients and stop the use of such a common and useful drug, heparin, when thrombocytopenia is not in fact due to this cause.

Conflict of interest No conflict of interest