Prospective evaluation of the '4Ts' score and particle gel immunoassay specific to heparin/PF4 for the diagnosis of heparin-induced thrombocytopenia.
BACKGROUND
Heparin-induced thrombocytopenia (HIT) is a severe disease that is often difficult to diagnose. A clinical scoring system, the '4Ts' score, has been proposed to estimate its probability before laboratory testing, and a particle gel immunoassay (H/PF4 PaGIA) has also been developed for rapid detection of HIT antibodies.


OBJECTIVE
To evaluate the performance of both methods when HIT is suspected clinically.


METHODS
Two hundred thirteen consecutive patients were included in four centers. The probability of HIT was evaluated using the 4Ts score blind to antibody test results. HIT was confirmed only when the serotonin release assay (SRA) was positive.


RESULTS
The risk of HIT was evaluated by the 4Ts score as low (LowR), intermediate (IR) or high (HR) in 34.7%, 60.6% and 4.7% of patients, respectively. The negative predictive value (NPV) of the 4Ts score was 100%, as the SRA was negative in all LowR patients. PaGIA was negative in 176 patients without HIT (99.4%, NPV) and the negative likelihood ratio (LR-) was 0.05. PaGIA was positive in 37 patients, including 21 with HIT (positive predictive value = 56.8%), with a positive LR of 11.4. A negative PaGIA result decreased the probability of HIT in IR patients from 10.9% before assay to 0.6%, whereas a positive result did not substantially increase the likelihood for HIT.


CONCLUSIONS
The use of the 4Ts score with PaGIA appears to be a reliable strategy to rule out HIT.
Pouplard
C
C
Department of Hematology, CHRU de Tours, Tours, France.
Gueret
P
P
Fouassier
M
M
Ternisien
C
C
Trossaert
M
M
Régina
S
S
Gruel
Y
Y
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000936:Antigen-Antibody Complex / Q000097:blood; D001323:Autoantibodies / Q000097:blood; D004342:Drug Hypersensitivity / Q000097:blood / Q000175:diagnosis / Q000209:etiology / Q000276:immunology; D005260:Female; D006493:Heparin / Q000009:adverse effects* / Q000276:immunology*; D006801:Humans; D007118:Immunoassay / Q000379:methods* / Q000706:statistics & numerical data; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D008875:Middle Aged; D010978:Platelet Factor 4 / Q000276:immunology* / Q000378:metabolism; D011237:Predictive Value of Tests; D011446:Prospective Studies; D016553:Purpura, Thrombocytopenic, Idiopathic / Q000097:blood / Q000175:diagnosis* / Q000209:etiology* / Q000276:immunology; D012680:Sensitivity and Specificity
D000936:Antigen-Antibody Complex; D001323:Autoantibodies; D007074:Immunoglobulin G; D010978:Platelet Factor 4; D006493:Heparin