Buku Haematology

Prolonged PT

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Prolonged APTT

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Prolonged APTT flowchart

Monitoring LMWH

Quick tip; Low Molecular Weight Heparin (LMWH) monitoring should be performed if suspicious of supratherapeutic or subtherapeutic treatment.

LMWH can be monitored with Anti-Xa levels if suspicion of inadequate treatment/overdosing. This occurs most commonly in these patient groups;

  • Extremes of weight
  • Renal impairment
  • Development of VTE on treatment
  • High risk of bleeding

To check adequate dosing;

  • Anti-Xa level taken 3-4 hours after a dose which has been given at that dose and time for at least 2 previous treatments (applies to once daily and split dose LWMH treatment). If there have not been 2 previous regular doses the result of the anti-Xa cannot be interpreted.
  • Normal target range is 0.5-1 IU/ml, but check local laboratory reference range, in the case of non-complex VTE. In complex cases such as recurrent VTE while on anticoagulant therapy, it may be beneficial to aim for a higher target anti-Xa, such as nearer 1 IU/ml, but these cases should be discussed with haematology 
  • Dose can then be increased or decreased by 10-20% for a level lower than reference range/desired or a level higher than the reference range respectively. Check anti-Xa again after a further 3 doses to assess response

If concerns about accumulation of LMWH due to renal impairment;

  • Trough levels pre-dose
  • Aim for level <0.1 IU/ml

Split dosing of LMWH can be used if;

  • Patients are needing large doses due to increased bodyweight to spread the large anticoagulant effect more evenly over 24 hours
  • Patients are at high risk of bleeding and there may be benefit in giving the dose twice daily to have a smaller circulating volume of anticoagulant at any one time

DIC

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HIT

Quick Tip; The 4 T's score for HIT is a validated score to guide management

Heparin induced thrombocytopenia (HIT) is a phenomenon induced by antibodies to platelets which are formed after heparin exposure. This can occur either during the first exposure episode or up to 100 days later, with a quicker onset of thrombocytopenia, once re-exposed. A thorough history is therefore critical to identify any history of exposure to heparin in any form over the previous 100 days.

HIT should be suspected in any patient who develops thrombocytopenia after being being exposed to heparin. Differential diagnosis (in often very unwell patients) include;

  • Spurious result- always send a second sample if thrombocytopenia is identified
  • Platelet consumption by sepsis or trauma
  • Disseminated intravascular coagulation
  • Thrombotic thrombocytopenic purpura

Workup

  • Repeat full blood count with blood film
  • Coagulation screen to look for DIC
  • If HIT seems the most likely diagnosis, perform a 4 T's score for HIT (a validated score available from textbooks or online calculators). This calculates the probably of thrombocytopenia being due to HIT, including consideration of alternative causes (Note if exposure to heparin in the previous 100 days, the time to development of thrombocytopenia can be shorter than if no recent exposure)

If the HIT score is intermediate or high this will usually merit a HIT blood test. Depending on laboratory processes, there is usually a high sensitivity, intermediate specificity screening test, and if positive the sample will be sent for further, more specific testing.

If the score is low, it is unlikely to be HIT but if other diagnoses seem very improbable discuss with haematology.

Links; BSH Guideline 

 

VTE risk in travellers

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Unprovoked VTE Ix

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