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A Practical Guide to Haemostasis


The HIT Expert Probability [HEP] Score

Introduction

The HIT Expert Probability [HEP] score was constructed based upon the opinions of 26 experts in this area. With a cut-off HEP score of 2, the algorithm was 100% sensitive and 60% specific for a diagnosis of HIT as defined by the expert panel.


The HEP Score:


Select Criteria:

Fall in Platelet Count from Peak Platelet Count to the Nadir Platelet Count since Heparin Exposure
<30%
-1 Point
30% - 50%
1 Point
>50%
3 Points
Timing of the Fall in Platelet Count
i. For patients in whom typical onset HIT is suspected
Fall in platelet count occurs <4 days after exposure to heparin
-2 Points
Fall in platelet count occurs 4 days after exposure to heparin
2 Points
Fall in platelet count occurs 5-10 days after exposure to heparin
3 Points
Fall in platelet count occurs 11-14 days after exposure to heparin
2 Points
Fall in platelet count occurs >14 days after exposure to heparin
-1 Point
ii. For patients with previous Heparin exposure within 100 days and in whom rapid onset HIT is suspected
Fall in platelet count occurs <48 hrs after exposure to heparin
2 Points
Fall in platelet count occurs >48 hrs after exposure to heparin
-1 Point
Nadir Platelet Count
≤ 20 x 109/L -2 Points
>20 x 109/L
2 Points
Thrombosis
i. For patients in whom typical onset HIT is suspected
New venous or arterial thrombosis ≥4 days after heparin exposure
3 Points
Progression of venous or arterial thrombosis whilst receiving heparin
2 Points
ii. For patients with previous Heparin exposure within 100 days and in whom rapid onset HIT is suspected
New venous or arterial thrombosis ≥4 days after heparin exposure
3 Points
Progression of venous or arterial thrombosis whilst receiving heparin
2 Points
Skin necrosis at subcutaneous Heparin Injections site[s]
Yes
3 Points
No
0 Points
Acute Systemic Reaction after iv Heparin infusion
Yes
2 Points
No
0 Points
Bleeding [Bleeding/petechiae or bruising]
Yes
-1 Point
No
0 Points
Other causes of Thrombocytopaenia not evident [Select all that apply]
Presence of a chronic thrombocytopenic disorder
-1 Point
Newly commenced treatment [non-heparin] known to cause thrombocytopaenia]
-2 Points
Severe infection
-2 Points
DIC [Fibrinogen <1g/L & D-dimer >5.0µg/mL
-2 Points
Indwelling arterial device
-2 Points
Cardiopulmonary bypass within 96hr
-1 Point
No other cause identified
3 Points


Score
[Max score 19]

HEP Score1
2 With a cut-off HEP score of 2, the HEP score was..
   Sensitivity: 100%
   Specificity: 60%
..for a diagnosis of Heparin Induced Thrombocytopaenia [HIT]

5 With a cut-off HEP score of 5, the HEP score was..
   Sensitivity: 86%
   Specificity: 88%
..for a diagnosis of Heparin Induced Thrombocytopaenia [HIT]

1 See Ref 1 Cuker et al 2010.

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