Impact of the patient population on the risk for heparin-induced thrombocytopenia

Abstract

The frequency of immune heparin-induced thrombocytopenia (HIT) varies among prospective studies. It is unknown whether this is caused by differences in the heparin preparations, the patient populations, or the types of serologic assay used to confirm the diagnosis. Seven hundred forty-four patients were studied from 3 different clinical treatment settings, as follows: unfractionated heparin (UFH) during or after cardiac surgery (n = 100), UFH after orthopedic surgery (n = 205), and low-molecular-weight heparin (LMWH) after orthopedic surgery (n = 439). Both an activation assay and an antigen assay were used to detect heparin-dependent IgG (HIT-IgG) antibodies. By activation assay, the frequency of HIT-IgG formation ranged from a low of 3.2% in orthopedic patients receiving LMWH to a high of 20% in cardiac patients receiving UFH; by antigen assay, the corresponding frequencies ranged from 7.5% to 50%. Both UFH use (P = .002) and cardiac surgery (P = .01) were more likely to be associated with HIT-IgG formation. However, among patients in whom HIT-IgG formed and who were administered UFH, the probability for HIT was higher among orthopedic patients than among cardiac patients (by activation assay: 52.6% compared with 5%; odds ratio, 21.1 [95% CI, 2.2-962.8]; P = .001; by antigen assay: 34.5% compared with 2.0%; odds ratio, 25.8 [95% CI, 3.2-1141]; P < .001). It is concluded that there is an unexpected dissociation between the frequency of HIT-IgG formation and the risk for HIT that is dependent on the patient population. HIT-IgG antibodies are more likely to form in patients who undergo cardiac surgery than in orthopedic patients, but among patients in whom antibodies do form, orthopedic patients are more likely to develop HIT.

The diagnosis and management of heparin‐induced thrombocytopenia in Japan

“…Although all patients had received intravenous heparin, the duration of exposure to heparin was variable among them Our multivariate analysis suggested that the duration of exposure to heparin and the thromboembolic complications tended to be associated with the level of optical density in the immunoassay. Regarding the primary disease and the clinical background of these patients, the incidence of HIT was higher among those receiving cardio‐vascular surgery compared to the internal medicine patients, which is compatible with the previous reports . The rate of anti‐PF4/heparin antibody formation, as detected by the immunoassays, was found to be not higher than the reported data.…”

“…Various risk factors of HIT in heparin‐treated adults are reported , and it is known that the different types of heparin as well as the patient‐related factors may affect the development of HIT. In our cases of non‐hemodialysis Japanese patients with suspected HIT, the median age was 66 years (mean 57, range 0–97), and the male/female ratio was almost 1:1 (53 males; 54 female).…”

HEPARIN‐INDUCED THROMBOCYTOPENIA IN DIALYSIS: The Pathophysiology of Immune‐mediated Heparin‐induced Thrombocytopenia

“…The frequency of HIT has also been shown to vary among different patient populations (15). Warkentin et al (15) studied 744 patients from three different clinical settings: unfractionated porcine heparin during or after cardiac surgery; unfractionated porcine heparin following orthopedic surgery; and low molecular weight heparin after orthopedic surgery (Table 1). In patients administered unfractionated heparin the frequency of HIT was 4.9% in the orthopedic patients and 1% in the cardiac patients.…”

“…If one combines all six studies, a total of 21 patients were found to have a positive test for the HIT antibody (2.6%). This is a low rate of HIT antibody positivity compared to patients after cardiac or orthopedic surgery (Table 1) (15). Very few of the dialysis patients were noted to be thrombocytopenic ( n = 6) and none had severe thrombotic complications.…”

“…Of these, ELISA is most commonly used. ELISA has comparable sensitivity to washed platelet functional assays but questionable specificity in that antibodies are detected in many susceptible patients in the absence of thrombocytopenia and thromboembolic complications, especially in those undergoing cardiac surgery (15). Sensitivity may be higher if the assay is repeated several days after heparin is withdrawn because free antibody may not be detected while the heparin‐PF4 complex is still present (32).…”