Thrombocytopenia in medical–surgical ICU patients

Background

Thrombocytopenia may be a marker of severe illness or a predictor of poor outcome in critically ill medical–surgical ICU patients.

Objective

To estimate the prevalence, incidence, risk factors for, and consequences of thrombocytopenia (defined as platelets < 150 × 10⁹/l).

Design

A longitudinal cohort study from January 2001 to January 2002.

Setting

A 15-bed medical–surgical ICU in Hamilton, Canada.

Methods

We enrolled consecutive patients age > 18 years expected to be in the ICU for > 72 hours. Patients were excluded if they had an admitting diagnosis of trauma, orthopedic surgery, cardiac surgery, pregnancy, or palliative care. To identify independent risk factors for thrombocytopenia and mortality, we used backwards stepwise elimination Cox regression analysis.

Results

Of 261 patients (mean APACHE II score = 25.5 ± 8.4), 116 (44%, 95% confidence interval [CI] = 38-51%) had thrombocytopenia (27% [22–33%] on ICU admission, and 17% [13–22%] developed it during the ICU stay). Patients with thrombocytopenia versus those without were more likely to require mechanical ventilation (100% vs 87%, P = 0.05) and platelet transfusion (7% vs 0%, P = 0.03), and less likely to receive heparin (18% vs 31%, P = 0.02). Among 34 risk factors, the independent risk factors for thrombocytopenia development during the ICU was ASA or nonsteroidal anti-inflammatory drug use (hazard ratio [HR] = 3.0, 95% CI = 1.4-6.5) and dialysis (HR = 3.0 [1.1–7.1]); conditions such as severe sepsis were not predictive. Among 261 patients, 33 (13%) patients had 36 heparin-induced thrombocytopenia tests (serotonin release assay); none were positive. Patients who ever developed thrombocytopenia versus those who did not had a long stay ICU stay (12 days vs 8 days), but a similar hospital stay (30 days vs 23 days), ICU mortality (31% vs 24%), and hospital mortality (46% vs 34%). A platelet count < 150 × 10⁹/l was not independently predictive of mortality after adjusting for age and illness severity (HR = 1.0 [0.6–1.7]), whereas platelet count < 50 × 10⁹/l was (HR 8.3 [3.8–18.3]).

Conclusions

In medical–surgical ICU patients, thrombocytopenia is common, associated with an increased duration of ICU stay, but not an increased risk of mortality until the platelet count is < 50 × 10⁹/l.