Platelet measurements versus discharge diagnoses for identification of patients with potential drug-induced thrombocytopenia: A cross-sectional study in the Netherlands

Background: In pharmacoepidemiological studies on the risk of drug-induced blood dyscrasias, including drug-induced thrombocytopenia (DIT), hospital discharge diagnoses have been used to identify potential cases. One of the possible limitations of discharge diagnoses is that due to incomplete registration not all potential cases are identified, which may limit statistical power. Clinical laboratory data have been suggested as a data type that is potentially more sensitive for identifying potential cases of adverse drug reactions than discharge diagnoses. Objective: To compare the number of patients with potential DIT that could be identified by using platelet measurements with the number of patients with potential DIT that could be identified by using discharge diagnoses for thrombocytopenia within a population of hospitalized patients. Methods: The study population of this cross-sectional study comprised all patients admitted to the University Medical Center Utrecht in 2004 and 2005, as captured within the Utrecht Patient Oriented Database (UPOD). The ratio of the number of patients with potential DIT based on platelet measurements (≥1 platelet count below 100 × 109/L without alternative diagnoses for DIT) to the number of patients with potential DIT based on discharge diagnoses for thrombocytopenia (International Classification of Diseases, 9th Revision, Clinical Modification [ICD-9-CM] codes 287.3-287.5 without alternative diagnoses for DIT) was determined. Results: Within the study period there were 56 411 hospitalizations. 2817 patients (5.0%) had ≥1 platelet count below 100 × 109/L. In 96.3% of these patients, alternative diagnoses for DIT were present, resulting in 103 (0.2%) patients with potential DIT based on platelet measurements. There were 74 patients (0.1%) with a discharge diagnosis for thrombocytopenia. In 81.1% of these patients, alternative diagnoses for DIT were present, resulting in 14 (0.02%) patients with potential DIT based on discharge diagnoses. This resulted in a ratio of the number of patients with potential DIT based on platelet measurements to the number of patients with potential DIT based on discharge diagnoses for thrombocytopenia of seven. Conclusion: This study showed that the use of platelet measurements is a more sensitive approach to the identification of patients with potential DIT than the use of discharge diagnoses for thrombocytopenia. © 2009 Adis Data Information BV. All rights reserved.