LAS VEGAS – High body mass index is strongly associated with increased rates of heparin-induced thrombocytopenia, based on findings from a review of prospectively collected data from surgical and cardiac intensive care unit patients presumed to have the condition.
Of 304 patients included in the review, 36 (12%) were positive for heparin-induced thrombocytopenia (HIT). The rates increased in tandem with BMI. For example, the rate was 0% among 9 underweight individuals (BMI less than 18.5 kg/m2), 8% among 119 normal-weight individuals (BMI of 18.5-24.9 kg/m2), 11% among 98 overweight individuals (BMI of 25-29.9 kg/m2), 18% among 67 obese individuals (BMI of 30-39.9 kg/m2), and 36% among 11 morbidly obese individuals (BMI of 40 kg/m2 or greater), Dr. Matthew B. Bloom reported at the annual meeting of the American Association for the Surgery of Trauma.
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Structure of the PF4 protein. Based on PyMOL rendering of PDB
The odds of HIT were 170% greater among obese patients, compared with normal-weight patients (odds ratio, 2.67), and 600% greater among morbidly obese patients, compared with normal-weight patient (odds ratio, 6.98), said Dr. Bloom of Cedars-Sinai Medical Center, Los Angeles.
Logistic regression showed that each 1 unit increase in BMI was associated with a 7.7% increase in the odds of developing HIT, he noted.
Additionally, an anti-heparin/PF4 (platelet factor 4) antibody OD (optical density) value of 2.0 or greater, but not of 0.4 or greater or 0.8 or greater, was also significantly increased with BMI, and in-hospital mortality increased significantly with BMI above normal, he said.
Warkentin 4T scores used to differentiate HIT from other types of thrombocytopenia were not found to correlate with changes in BMI in this study, nor were deep vein thrombosis, pulmonary embolism, or stroke.
The increase in PF4 with increasing BMI may be a marker for overall increasing levels of circulating antibodies in the obese ICU population, but more biochemical studies are needed to tease this out, he said.
Patients included in the review were all those admitted to the surgical and cardiac ICUs at Cedars-Sinai over a more than 7 year period. They had a mean age of 62.1 years, 59% were men, and their mean BMI was 27 kg/m2.
The findings are among the first to show a strong association between BMI and HIT in ICU patients, Dr. Bloom said, noting that several other studies have shown that obesity is linked with increased incidence and increased severity of immune-mediated diseases, including rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease.
“And HIT is an immune-mediated disease,” he added.
“BMI may be an important new clinical variable for estimating the pre-test probability of HIT, and perhaps, in the future, patient ‘thickness’ could be considered a new ‘T’ in the 4T score, he concluded.
Dr. Bloom reported having no disclosures.