Aim — to evaluate an effectiveness of 4T algorithm and antigenic laboratory tests for the diagnosis of HIT type II in patients at multifield surgical hospital. Material and methods. It was performed a retrospective analysis of the effectiveness of clinical-laboratory algorithm for HIT diagnosis. Detection of the antibodies to heparin-TF4 complexes was carried out in 33 patients. Results. Postoperative platelets number monitoring is the key for timely diagnosis of HIT type II. An attempt to diagnose HIT without laboratory confirmation by antigenic tests leads to overdiagnosis and unjustified withdrawal of heparin therapy. Antigenic tests with 4T criterion contribute to early diagnosis of HIT and allow to change timely treatment strategy in order to prevent potentially fatal complications. Diagnostic algorithm eliminated HIT in 28 (85%) out of 33 patients with moderate or high risk according to 4T criterion that helps to prevent unjustified changes in anticoagulant therapy. Conclusion. In any hospital the doctors need to be aware of the risks of the occurrence, diagnosis and treatment of HIT type II. Postoperative platelets number monitoring is the key for timely diagnosis of HIT type II. Detection of the antibodies to heparin-TF4 complexes performed timely and according to indications (based on 4T criterion) allows to avoid overdiagnosis of HIT and to change timely treatment strategy in order to prevent potentially fatal complications.