Heparin Induced Thrombocytopenia ( HIT ) Screen

Coagulation

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Description

HIT is an immunologically mediated complication that occurs with both unfractionated heparin (UFH) and to a lesser extent with low molecular weight heparin (LMWH). The fundamental clinical paradox of HIT is that despite thrombocytopenia (which would normally be associated with a risk of bleeding), the major clinical complications are thrombotic, affecting both the arterial and venous circulation; deep vein thrombosis (DVT) and pulmonary embolism (PE) being the most common events, although arterial events such as stroke and myocardial infarction may also occur.

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Indications

HIT usually features a platelet count fall of more than 50% (from the peak count after day 4 of heparin therapy), newly presenting thrombosis, typically occurring within 5 to 14 days of heparin exposure or within hours if the patient has had recent exposure to heparin. When HIT is suspected it is essential that the current heparin therapy is immediately stopped but is it is mandatory that the patient remains on an alternative anticoagulant to prevent any further thrombosis. The clinical consequences of HIT and the risks of the alternative anticoagulant therapies mean it is essential that a confirmed diagnosis of HIT is made. HIT should be diagnosed on the basis of clinical presentation and laboratory results. Initially the likelihood of HIT is based on clinical findings. A scoring system model, referred to as the ‘Four Ts, based on the degree of thrombocytopenia, the timing, the development of new or extended thrombosis and whether there may be another reason for the thrombocytopenia should be used to assess the likelihood of HIT, as either low, intermediate or high. If the scoring system indicates the probability is high, then the current heparin therapy must be stopped immediately and an alternative therapy used whilst laboratory tests confirm the suspected diagnosis.

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Sample Type

1 x sodium citrate 3.2% or 1 x serum sample (both equally acceptable).

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Reference Range

HIT cannot be excluded for results ≥ 1.0 u/ml.

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Turnaround Time

Within1 hour

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Testing Frequency

As required. All samples are treated as urgent by the laboratory upon receipt.

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External Notes

It is desirable for all requests to be accompanied with a 4T Score. Download Scoring Card

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Patient Preparation

Plasma heparin levels should be below 1iu/ml before taking the sample.

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References

Greinacher A, Warkentin (2006). Recognition, treatment, and prevention of heparin-induced thrombocytopenia: Review and update Thrombosis Research Volume 118, Issue 2, 2006, Pages 165-176.
Watson H et al. ( 2012 ). Guidelines on the diagnosis and management of heparin induced thrombocytopenia: Second Edition. British Journal of Haematology Guideline.

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.