Diagnosis of heparin-induced thrombocytopenia
| Consider HIT whenever a patient exposed to heparin (or has reasonably supposition of exposure): |
| Has a significant fall in platelet count and/or |
| Has new blood clot |
| Formulate clinical probability estimate (4Ts score awards 0-2 points for each of the following parameters): |
| Thrombocytopenia, is it typical (at least 30% to 50% fall) |
| Timing of platelet fall (5-12 d after heparin initiation; consider also alternate temporal scenarios) |
| Thrombotic complications contemporaneously (consider more strongly if unusual sites) |
| Other likely explanations for low platelets and/or clots |
| If moderate or strong suspicion, order serologic test (ELISA): |
| <0.4, “negative”; 0.4-1.0, <2% to 5% have platelet-activating antibodies |
| 1.0-1.4, 10% to 20% have activating antibodies; 1.4–2.0, 50% have activating antibodies |
| >2.0, 90% have activating antibodies |
| If diagnosis is clear on the basis of clinical probability and ELISA (great majority), no need for confirmatory serology. |
| If clinical probability is low, there is no reason for ordering serologic tests (can lead to harm). |
| Consider HIT whenever a patient exposed to heparin (or has reasonably supposition of exposure): |
| Has a significant fall in platelet count and/or |
| Has new blood clot |
| Formulate clinical probability estimate (4Ts score awards 0-2 points for each of the following parameters): |
| Thrombocytopenia, is it typical (at least 30% to 50% fall) |
| Timing of platelet fall (5-12 d after heparin initiation; consider also alternate temporal scenarios) |
| Thrombotic complications contemporaneously (consider more strongly if unusual sites) |
| Other likely explanations for low platelets and/or clots |
| If moderate or strong suspicion, order serologic test (ELISA): |
| <0.4, “negative”; 0.4-1.0, <2% to 5% have platelet-activating antibodies |
| 1.0-1.4, 10% to 20% have activating antibodies; 1.4–2.0, 50% have activating antibodies |
| >2.0, 90% have activating antibodies |
| If diagnosis is clear on the basis of clinical probability and ELISA (great majority), no need for confirmatory serology. |
| If clinical probability is low, there is no reason for ordering serologic tests (can lead to harm). |
ELISA, enzyme-linked immunosorbent assay; HIT, heparin-induced thrombocytopenia; 4Ts score, thrombocytopenia, timing after beginning heparin, whether accompanying thromboses or other sequelae are present, and whether other explanations are possible or likely.