Question

A patient underwent thrombectomy of femoro popliteal segment with poor outflow and was on heparin infusion. His platelet count dropped from 2 lakhs to 1 lakh/mm$^3$ on 6th day of infusion. Other blood parameters were normal and there was no feature of sepsis/infection.
How will you confirm your diagnosis?

Hint:

When diagnosing HIT, a positive PF4-heparin ELISA or serotonin release assay confirms the diagnosis, especially when clinical suspicion is high.

Answer 1

Step 1: Clinical suspicion.
The diagnosis of HIT is primarily based on clinical suspicion. In this case, the patient’s platelet count dropped significantly after 6 days of heparin therapy, and there is no sign of infection or other causes of thrombocytopenia, which strongly suggests HIT.

Step 2: Confirmatory tests.
1. Heparin-induced platelet aggregation test (HIP: This test detects antibodies that cause platelet activation in the presence of heparin. It is a specific test but not always readily available.
2. Serotonin release assay (SR: This is the gold standard test for confirming HIT, as it measures the ability of antibodies to activate platelets in the presence of heparin.
3. PF4-heparin ELISA: This enzyme-linked immunosorbent assay detects antibodies to the PF4-heparin complex and is commonly used in clinical practice. A positive result is highly suggestive of HIT, though it may not confirm the condition in all cases.

Step 3: Conclusion.
To confirm HIT, a serotonin release assay (SR or PF4-heparin ELISA should be performed. If these tests are positive, it confirms the diagnosis of HIT.