HIT 4T score

NOTE: Whilst we have done our utmost to ensure the accuracy of the data in this section, users should access the original publications. This will also allow you to see how the algorithm was created, the population studied and any limitations to the study.

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1. See also HIT assays.

1. Lo GK, Juhl D, et al. Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost. 2006; 4: 759-65.

2. Warkentin, T.E. (2003) Management of heparin-induced thrombocytopenia: a critical comparison of lepirudin and argatroban. Thromb Res, 110, 73-82.

3. Warkentin, T.E. (2003) Heparin-induced thrombocytopenia: pathogenesis and management. Br J Haematol, 121, 535-555.

4. Warkentin, T.E., Greinacher, A., Koster, A. & Lincoff, A.M. (2008) Treatment and prevention of heparin-induced thrombocytopenia: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest, 133, 340S-380S.

5. Warkentin TE, Sheppard JI, Raschke R, et al. Performance characteristics of a rapid assay for anti-PF4/heparin antibodies: the particle immunofiltration assay. J Thromb Haemost. 2007;5(11):2308-10.

6. Zheng G, Streiff MB, et al. A novel diagnostic algorithm for heparin-induced thrombocytopenia. International Journal of Laboratory Hematology. 2018;40:527-532.

7. Nagler M and Angelillo-Scherrer A. Diagnostic value of the 4Ts score for heparin-induced thrombocytopenia in the critically ill. Journal of critical care. 2014; 29: 1126-7.

8. Linkins LA, Bates SM, et al. Combination of 4Ts score and PF4/H-PaGIA for diagnosis and management of heparin-induced thrombocytopenia: prospective cohort study. Blood. 2015; 126: 597-603.

Platelet Count
	>50% fall in platelet count or a platelet nadir of 20-100 x 10⁹/L	2 Points
	30-50% in platelet count or a platelet nadir of 10-19 x 10⁹/L	1 Point
	<30% fall in platelet count or a platelet nadir of <10 x 10⁹/L	0 Points
Timing
	Onset with 5-10 days of exposure to heparin or <1 day if previous exposure to heparin within 100 days	2 Points
	Unclear - Platelet count falls after 10 days	1 Point
	Platelet count falls too early and without recent exposure to heparin	0 Points
Thrombosis
	New thrombosis Skin necrosis	2 Points
	Progressive or recurrent thrombosis Some skin lesions e.g. erythema	1 Point
	None	0 Points
Other causes of Thrombocytopaenia not evident
	No other cause identified	2 points
	Possible other cause	1 point
	Other cause clearly identifiable	0 points

4T Score
0-3	Low Risk
4-5	Intermediate Risk
6-8	High Risk

4T Score + PF4-Heparin ELISA OD
4T Score	PF4-Heparin ELISA OD	Sensitivity & Specificity
8	OD ≥1.0	Sensitivity 75% Specificity 98%
6 - 7
4 - 5	OD ≥2.0

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