National US estimates of recombinant tissue plasminogen activator use: ICD-9 codes substantially underestimate

Current US estimates of recombinant tissue plasminogen activator (rt-PA) use have been based either on extrapolation of regional studies or on administrative database estimates, both of which may have inherent biases. We sought to compare the utilization of rt-PA in acute ischemic stroke in the MEDPAR database to another national hospital database with drug utilization information.

Cases were defined as DRG 14,15, and 524 and ICD-9 code 99.1, which indicates cerebral thrombolysis, for fiscal year 2001 to 2004. Additionally, the Premier database was queried for rt-PA utilization documented in pharmacy records in those patients admitted for stroke. Change over time and difference between databases were tested using Poisson regression.

When comparing databases, rt-PA use, as identified by ICD-9 code 99.1, was only documented in 0.95% of stroke cases in 2004 in MEDPAR, and 1.2% in the Premier database, which slightly increased by 0.04% to 0.09% over time. Analysis of pharmacy billing records increased the estimate to 1.82%. Exclusion of cases younger than 65 years excluded 43% of cases treated with rt-PA. In 2004, 12.7% of cases receiving thrombolytic had either a TIA or a hemorrhagic stroke ICD-9 code.

We estimate the rate of rt-PA use in the United States to be 1.8% to 2.1% of ischemic stroke patients. The rate of thrombolytic use for ischemic stroke was slightly increasing between 2001 and 2004 at a rate of 0.04% to 0.09% per year. A significant proportion of patients treated with rt-PA are likely miscoded as either TIA or hemorrhagic stroke. We conservatively estimate that 10,800 to 12,600 patients received rt-PA in 2004.