aThrombocytopenia defined as platelet count fall >50% from baseline. bHIPA positive in 3/41 (7.3%) of ElA-positive sera.

Two patients with HIT antibodies had mild thrombocytopenia, but a causal relation to heparin was not stated.

dResults of platelet aggregation testing are not included since there was a false positive rate of 33% in control uremic patients not yet exposed to heparin. eRepeat samples on 71 patients were taken 6-8 month after initial sampling of 100 patients. 'Twelve of 22 EIA positive sera also tested positive by SRA

9Pediatric HD patients—seropositivity seems to be highest in earlier months of HD, then antibody gradually disappears, incidence of HIT antibodies may have been underestimated since testing was performed on samples from day 3-4. 'Yeh et al., 2006, and Foo et al., 2006, describe similar inception cohorts with a baseline prevalence of HIT-lg of 15/500 (3.0%). 'Values listed indicate new seroconversions; of the inception cohort of 154, 7 (4.5%) were ElA-positive at baseline.

kOf patients undergoing PCI, 20/163 (12.3%) were ElA-positive; Of the non-PCI patients, 2/89 (2.2%) were ElA-positive; 22/252 represents new seroconversions (2/254 [0.8%] EIA positive at baseline).

'20% serotonin release used in Warkentin et al., 2000, rather than 50% serotonin release cutoff used in Warkentin et al., 1995. m10/265 (3.8%) were found to have HIT-lg prior to surgery.

"Ten patients had HIT-IgG preoperatively: incidence of new seroconversion was 17/44 (38.6%). "Incidence of new seroconversion was 43% for EIA and 9% for SRA.

Two patients had HIT-IgG preoperatively: incidence of new seroconversion was 12/51 (23.5%) for EIA-lgM/A/G and 7/51 (13.7%) for ElA-lgG. None had a positive aggregation assay preoperatively.

q80.2% underwent CPB, remainder "off-pump" surgery; 18.8% received postoperative UFH, LMWH, or both.

'Excludes patients testing positive for HIT antibodies at baseline. i—

Two patients had HIT-IgG preoperatively. Incidence of new seroconversion was 1/54 (1. 9%). S

'Includes only HIPA patients who also tested positive in EIA. SJ

"Pediatric cardiac surgery; EIA testing was performed preoperatively in patients prior to a second surgery for congenital heart defects. Q.

Abbreviations-. CPB, cardiopulmonary bypass; EIA, PF4-heparin enzyme-linked immunosorbent assay (-IgM/A/G, one or more of IgM, IgA, and IgG antibodies present; -IgG, IgG ^

antibodies only present); HIPA, heparin-induced platelet activation assay; HIT, heparin-induced thrombocytopenia; iv ther, intravenous therapeutic-dose heparin; LMWH, low j.

molecular weight heparin; Ml, myocardial infarction; NPH, no postoperative heparin; PCI, percutaneous coronary intervention; PRP, HIT assay using citrated platelet-rich ®

plasma; RCT, randomized controlled trial; sc proph, subcutaneous prophylactic dose heparin; SRA, serotonin release assay using washed platelets; UFH, unfractionated heparin; g-

VAD, ventricular assist device; VTE, venous thromboembolism.

HIT "Iceberg"

HIT "Iceberg"

waterline waterline

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