Early-onset and persisting thrombocytopenia in post-cardiac surgery patients is rarely due to heparin-induced thrombocytopenia, even when antibody tests are positive.
BACKGROUND
The high frequency of thrombocytopenia in post-cardiac surgery patients makes it challenging to diagnose heparin-induced thrombocytopenia (HIT). Two platelet count profiles are reported as indicating possible HIT in these patients: profile 1 describes a platelet count fall that begins between postoperative days 5 and 10, whereas profile 2 denotes early-onset thrombocytopenia that persists beyond day 5.


OBJECTIVE
To examine how these platelet count profiles correlate with antibody status and HIT post-cardiac surgery.


METHODS
We prospectively screened 581 cardiac surgery patients for heparin-dependent antibodies by platelet factor 4 (PF4)-heparin immunoassay and platelet-activation test, and performed daily platelet counts (until day 10) with 30-day follow-up.


RESULTS
All three patients with platelet count profile 1 tested positive for platelet-activating anti-PF4-heparin IgG antibodies [odds ratio (OR) 521.7, 95% confidence interval (CI) 3.9-34,000, P = 0.002], and were judged to have HIT. In contrast, none of 25 patients with early-onset and persisting thrombocytopenia (profile 2) was judged to have HIT, including five patients testing positive for platelet-activating anti-PF4-heparin IgG antibodies. In these patients, the frequency of heparin-dependent antibodies did not differ from that in non-thrombocytopenic controls, either for anti-PF4-heparin IgG (OR 1.7, 95% CI 0.7-4.1, P = 0.31) or for platelet-activating antibodies (OR 1.9, 95% CI 0.6-5.7, P = 0.20). Multivariate analysis revealed that type of cardiac surgery, but not HIT antibody status, predicted early-onset and persisting thrombocytopenia. Together, these findings show that HIT was uncommon in this study population [overall frequency, 3/581 (0.5%), 95% CI 0.1-1.5%].


CONCLUSIONS
Thrombocytopenia that begins between 5 and 10 days post-cardiac surgery is highly predictive for HIT. In contrast, early-onset and persisting thrombocytopenia is usually caused by non-HIT factors with coinciding heparin-dependent antibody seroconversion.
Institut für Immunologie und Transfusionsmedizin, Ernst-Moritz-Arndt Universität, Greifswald, Germany.
S
S
Selleng
B
B
Malowsky
U
U
Strobel
A
A
Wessel
T
T
Ittermann
H-G
HG
Wollert
T E
TE
Warkentin
A
A
Greinacher
D000368:Aged; D000906:Antibodies / Q000097:blood; D000925:Anticoagulants / Q000009:adverse effects* / Q000276:immunology; D001792:Blood Platelets / Q000187:drug effects* / Q000276:immunology; D006348:Cardiac Surgical Procedures / Q000009:adverse effects*; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D005260:Female; D006493:Heparin / Q000009:adverse effects* / Q000276:immunology; D006801:Humans; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000097:blood; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D015539:Platelet Activation / Q000187:drug effects; D010976:Platelet Count; D010978:Platelet Factor 4 / Q000276:immunology; D011182:Postoperative Care; D011237:Predictive Value of Tests; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D013921:Thrombocytopenia / Q000097:blood / Q000139:chemically induced* / Q000175:diagnosis / Q000276:immunology; D013997:Time Factors
D000906:Antibodies; D000925:Anticoagulants; D007074:Immunoglobulin G; D010978:Platelet Factor 4; D006493:Heparin