Brief report: Laboratory safety monitoring of chronic medications in ambulatory care settings

OBJECTIVE: To evaluate laboratory safety monitoring in patients taking selected chronic prescription drugs. DESIGN., Retrospective study using 1999-2001 claims data to calculate rates of missed laboratory tests (potential laboratory monitoring errors). Eleven drugs/drug groups and 64 laboratory tests were evaluated. SETTING: Two staff/network model health maintenance organizations. PATIENTS: Continuously enrolled health plan members age >= 19 years taking >= 1 chronic medications. MEASUREMENTS AND MAIN RESULTS: Among patients taking chronic medications (N=29,823 in 1999, N=32,423 in 2000, and N=36,811 in 2001), 47.1% in 1999, 45.0% in 2000, and 44.0% in 2001 did not receive >= 1 test recommended for safety monitoring. Taking into account that patients were sometimes missing more than I test for a given drug and that patients were frequently taking multiple drugs, the rate of all potential laboratory monitoring errors was 849/ 1,000 patients/year in 1999, 810/1,000 patients/year in 2000, and 797/1,000 patients/year in 2001. Rates of potential laboratory monitoring errors varied considerably across individual drugs and laboratory tests. CONCLUSIONS: Lapses in laboratory monitoring of patients taking selected chronic medications were common. Further research is needed to determine whether, and to what extent, this failure to monitor patients is associated with adverse clinical outcomes.