The 4Ts scoring system for heparin-induced thrombocytopenia in medical-surgical intensive care unit patients.
BACKGROUND
Heparin-induced thrombocytopenia (HIT) is commonly considered but rarely confirmed in critically ill patients. The 4Ts score (Thrombocytopenia, Timing of thrombocytopenia, Thrombosis, and oTher reason) might identify individual patients at risk of having this disorder.


OBJECTIVE
The aim of the study was to evaluate the value of the 4Ts HIT score in comparison with the serotonin-release assay (SRA) in critically ill patients.


METHODS
This study describes the combined results of 3 prospective studies enrolling critically ill patients who were investigated for HIT if platelets fell to less than 50 x 10(9)/L or if platelet counts decreased to less than 50% of the value upon intensive care unit admission. We confirmed HIT by a positive platelet SRA. We assigned a 4Ts score blinded to SRA results to all 50 patients investigated for HIT; those with positive SRA results were scored in duplicate.


RESULTS
Of 528 patients, 50 (9.5%) were investigated for HIT; 39 (78%) of 50 (64%-88%) of these patients were scored as "low probability" by 4Ts score and none had a positive SRA. Of 49 patients who underwent SRA testing because of thrombocytopenia, only 2 (4.1%; 0.5-14.0) had a positive SRA (1 with a moderate 4Ts score and 1 with a high 4Ts score). Therefore, the overall incidence of HIT confirmed by SRA was 2 (0.4%) of 528 (0.04%-1.4%).


CONCLUSIONS
Significant thrombocytopenia during heparin administration occurred in 9.5% of critically ill patients, but HIT was confirmed in only 4.1% of those undergoing testing, for an overall incidence of 0.4%. A low 4Ts score occurred in 78% of patients investigated for HIT; none of these patients had a positive SRA. We conclude that HIT is uncommon in critically ill patients and that the 4Ts score is worthy of further evaluation in this patient population.
Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada. crowthrm@mcmaster.ca
Mark Andrew
MA
Crowther
Deborah J
DJ
Cook
Martin
M
Albert
David
D
Williamson
Maureen
M
Meade
John
J
Granton
Yoanna
Y
Skrobik
Stephan
S
Langevin
Sangeeta
S
Mehta
Paul
P
Hebert
Gordon H
GH
Guyatt
William
W
Geerts
Christian
C
Rabbat
James
J
Douketis
Nicole
N
Zytaruk
Joanne
J
Sheppard
Andreas
A
Greinacher
Theodore E
TE
Warkentin
D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000009:adverse effects*; D016638:Critical Illness; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D010976:Platelet Count; D011237:Predictive Value of Tests; D018570:Risk Assessment / Q000379:methods; D012701:Serotonin / Q000378:metabolism*; D013503:Surgery Department, Hospital; D013921:Thrombocytopenia / Q000139:chemically induced / Q000175:diagnosis* / Q000378:metabolism; D013927:Thrombosis / Q000175:diagnosis
D000925:Anticoagulants; D012701:Serotonin; D006493:Heparin