Heparin-Induced Thrombocytopenia

Published on 04/03/2015 by admin

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Chapter 58 Heparin-Induced Thrombocytopenia

Table 58-1 Risk Factors for Heparin-Induced Thrombocytopenia

Heparin type: Unfractionated > low-molecular-weight heparin > fondaparinux
Patient type: Postoperative (major > minor surgery) > medical > obstetric/pediatric
Dose*: Prophylactic dose > therapeutic dose > flushes
Duration: 11-14 days > 5-10 days > 4 days or fewer
Sex: Female > male

*Importance of heparin dose is uncertain because of confounding effect of patient type (e.g., postoperative patients tend to receive prophylactic-dose heparin whereas medical patients [e.g., with venous thromboembolism] are more likely to receive therapeutic-dose heparin); nevertheless, reported frequencies of heparin-induced thrombocytopenia (HIT) are relatively high in patients given postoperative prophylactic-dose heparin.

Heparin exposure beyond 14 days does not usually increase the risk of HIT beyond that of an 11- to 14-day exposure.

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Figure 58-2 CHARACTERISTIC TIMELINE OF HEPARIN-INDUCED THROMBOCYTOPENIA (HIT).

Anti-PF4/heparin antibodies (by enzyme immunoassay [EIA]) per postoperative day in 12 patients with HIT and 36 seropositive non-HIT control patients. A, Mean (±standard error of the mean [SEM]) optical density (OD) of anti-PF4/heparin antibodies detected using commercial immunoassay (EIA-GAM) that detects antibodies of all three immunoglobulin classes (IgG, IgA, IgM). HIT patients are indicated by image, and seropositive non-HIT controls by image. On each day beginning on postoperative day 6, there is a significant difference in the mean of the OD levels between the patients with HIT and the seropositive non-HIT controls (P < .05 by nonpaired t test). At the top of the figure, summary data for 12 HIT patient profiles are shown for four key events (first day of antibody detection, beginning of HIT-related platelet count fall, platelet count fall ≥50%, and thrombotic event), summarized as median (small purple squares within rectangles), interquartile range (rectangles), and range (ends of thin black lines). B, Mean (±SEM) OD values of anti-PF4/heparin antibodies detected using an in-house immunoassay (EIA-Ig) that detects antibodies of the individual immunoglobulin classes, IgG (red circles), IgA (green triangles), and IgM (blue inverted triangles) for HIT (solid symbols) and non-HIT (open symbols). On each postoperative day beginning on day 5, there is a significant difference in the mean of the OD units for the IgG immunoassay between the patients with HIT and the seropositive non-HIT controls (**P < .005 for days 6 to 10; *P < .05 for days 5, 11, and 12).

(From Warkentin TE, Sheppard JI, Moore JC, et al: Studies of the immune response in heparin-induced thrombocytopenia. Blood 113:4693, 2009.)