New Australian expert consensus guidelines on heparin- induced thrombocytopenia (HIT) put the emphasis on using the 4Ts score to rule out the prothrombotic condition and the need for laboratory testing.

Formulated by members of the Thrombosis and Haemostasis Society of Australia and New Zealand, the guidelines state that the 4Ts score has a high negative predictive value to exclude HIT and there is no need to perform further laboratory testing in patients who have a low score.

A high 4Ts score would result in a switch to from heparin to a non-heparin anticoagulant without an immunoassay.

Patients may also be allowed to continue heparin if they have a high 4Ts score but the immunoassay score is negative, they advise.

“The importance of examining both clinical and laboratory data in considering a diagnosis of HIT cannot be overstated,” the guidelines published in the MJA state.

Where patients are suspected of HIT, there are now many alternative new anticoagulant options such as anti factor Xa inhibitors and direct acting oral anticoagulants (DOACs), the statement notes.

Anti-Xa inhibitors or agatroban are an option for clinically unstable HIT patients, whereas fixed dose anticoagulants  such as fondaparinux are simpler options for stable patients, including those without thrombosis.

Therapeutic anticoagulation is advised for a minimum of three months in patients with HIT and thrombosis.

The main recommendations are:

1. A 4Ts score is recommended for all patients with suspected HIT prior to laboratory testing.
2. Further laboratory testing with a screening immunoassay or confirmatory functional assay is not recommended in individuals with a low 4Ts score. However, if there are missing or unreliable clinical data, then laboratory testing should be performed.
3. A positive functional assay result confirms the diagnosis of HIT and should be performed to confirm a positive immunoassay result.
4. Heparin exposure must be ceased in patients with suspected or confirmed HIT and initial treatment with a non-heparin alternative instituted.
5. Non-heparin anticoagulants used to treat HIT should be given in therapeutic rather than prophylactic doses.
6. DOACs may be used in place of warfarin after patients with HIT have responded to alternative parenteral anticoagulants with platelet count recovery.