Heparin-induced thrombocytopenia diagnostic criteria
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Heparin-induced thrombocytopenia |
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Differentiating Heparin-induced thrombocytopenia from other Diseases |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Shyam Patel [2]
Overview
Diagnostic Criteria
The 4T score
The current diagnostic algorithm for HIT involves calculation of the pre-test probability using the 4T score.[1] [2] This scoring system is used when a patient is found to have thrombocytopenia or thrombosis after heparin exposure. It is calculated before the heparin-PF4 IgG antibody is ordered, and it offers a cost-effective and efficient way for determining the likelihood of HIT.[3]
- Thrombocytopenia: 2 points are assigned to platelet count fall greater than 50% and platelet nadir greater than 20,000 per microliter. 1 point is assigned to platelet count fall 30-50% or platelet nadir 10,000-19,000 per microliter. No points are assigned to platelet count fall less than 30% or platelet nadir less than 10,000 per microliter.
- Thrombosis: 2 points are assigned to new confirmed thrombosis or skin necrosis at injection sites or acute systemic reaction after IV heparin bolus. 1 point is assigned to progressive or recurrent skin lesions or suspected thrombosis (without proof of thrombosis. No points are assigned if there is no thrombosis.
- Timing: 2 points are assigned if the platelet count fall clearly occurs between days 5 and 10, or if the platelet count fall occurs in less than 1 day if a patient had recent heparin exposure within the past 30 days. 1 point is assigned if the platelet count is likely to have fallen between days 5-10 (there may be missing platelet count checks), or platelet count fall after day 10, or platelet count fall within 1 day in the setting of prior heparin exposure 30-100 days ago. No points are assigned if platelet count fall occurs within 4 days in the setting of no heparin exposure.
- oTher: 2 points are assigned if there is no apparent alternative explanation of thrombocytopenia. 1 point is assigned if there is a possible alternative explanation of thrombocytopenia. No points are assigned if there is a definite alternative explanation of thrombocytopenia.
The range of scores is from 0 to 8. The points from each of the 4 categories is summed in order to obtain the final score, as follows:
- 0 to 3 points: low probability of HIT
- 4 to 5 points: intermediate probability of HIT
- 6 to 8 points: high probability of HIT
The American Society of Hematology, as part of the Choosing Wisely program, states[4]:
- "Don’t test or treat for suspected heparin-induced thrombocytopenia (HIT) in patients with a low pre-test probability of HIT."
Clinical and Laboratory Criteria
There are no well-established formal criteria for the diagnosis of HIT. However, there are clinical and laboratory criteria which can strongly suggest a diagnosis of HIT.
Clinical criteria for a diagnosis of HIT include[5]:
- Development of thrombocytopenia and/or thrombosis in the setting of recent heparin exposure
- Absence of other causes of thrombocytopenia
- Timing of thrombocytopenia (i.e. 5-14 days is most suggestive)
Laboratory criteria for diagnosis of HIT include[5]:
- Thrombocytopenia (i.e. a platelet count drop by > 50% with nadir > 20,000 per microliter is most suggestive)
- Presence of heparin-PF4 IgG antibodies via enzyme-linked immunoassay: A high PF4 IgG optical density is more suggestive of HIT than a low optical density. If the optical density is more than 2, a diagnosis of HIT is very likely. This should be confirmed via the functional assay.
- Presence of a positive functional assay (i.e. C14-serotonin release assay or heparin-induced platelet aggregation assay)
Reference
- ↑ Lo GK, Juhl D, Warkentin TE, Sigouin CS, Eichler P, Greinacher A (2006). "Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings". J Thromb Haemost. 4 (4): 759–65. doi:10.1111/j.1538-7836.2006.01787.x. PMID 16634744.
- ↑ Cuker A, Gimotty PA, Crowther MA, Warkentin TE (2012). "Predictive value of the 4Ts scoring system for heparin-induced thrombocytopenia: a systematic review and meta-analysis". Blood. 120 (20): 4160–7. doi:10.1182/blood-2012-07-443051. PMC 3501714. PMID 22990018.
- ↑ Gardiner EE, Andrews RK, Cuker A (2014). "DiagnoSTic assays for heparin-induced thrombocytopenia". Br J Haematol. 166 (5): 631–3. doi:10.1111/bjh.12940. PMC 4134688. PMID 24824208.
- ↑ The American Society of Hematology. test or treat for suspected heparin-induced thrombocytopenia (HIT) in patients with a low pre-test probability of HIT.. 2014
- ↑ 5.0 5.1 Arepally GM, Ortel TL (2010). "Heparin-induced thrombocytopenia". Annu Rev Med. 61: 77–90. doi:10.1146/annurev.med.042808.171814. PMC 4153429. PMID 20059332.