ICD-9-CM codes poorly indentified venous thromboembolism during pregnancy

Objective There is little data regarding the accuracy of pregnancy-specific ICD-9-CM codes used to identify patients with venous thromboembolism (VTE). Study design and setting We identified a large cohort of pregnant patients in whom there were one or more pregnancy-specific (600 codes) or standard ICD-9-CM codes (400 codes) for VTE. Charts of these cases were abstracted to determine the presence of objectively documented VTE. Results A total of 214 cases had a code for VTE either during pregnancy or the 6-week postpartum period; 82% had a pregnancy-specific code and 18% a standard code. Overall, 84 (39%, 95% CI=33-46%) had objectively documented VTE. A pregnancy-specific ICD-9-CM for VTE had a positive predictive value (PPV) of 54/174=31% (95% CI=24-38%), whereas standard VTE codes had a PPV of 30 of 38=80% (95% CI=63-99%). A PPV in the range of 95-100% could be attained using other criteria, at the expense of detecting only 28 to 45% of all VTE cases. Conclusions Pregnancy-specific ICD-9-CM codes for VTE have low PPV. Other criteria must be applied to select cases with a high probability of having objectively documented VTE.