Analytic performance of digoxin laboratory monitoring.

Since therapeutic drug monitoring is rapidly becoming a widely-used tool in clinical medicine we prospectively assessed 547 control samples over a period of 18 months using fluorescence polarization immunoassay, calibrators and control samples to determine the analytical performance of Abbott TDx in measuring serum digoxin levels. Recovery of the controls (within-run and between-run coefficient of variation) evaluated at the low, target therapeutic and intoxication ranges was 14%, 8% and 7% and precision was -3.57, -7.02, -3.38, respectively. Our clinical utility analysis showed that the prescribed dose provided serum digoxin levels within, above and below the targeted therapeutic range for 50.2%, 38.4% and 11.4% of the patients, respectively. The discrepancy between the calibrators and the controls, the tendency towards lower prescription dosage and patient noncompliance with the prescribed dose all account for these findings. The direct costs for digoxin serum concentration monitoring amount to 10 US $. A closer collaboration between the laboratory and the prescribing physician will undoubtedly form the basis of a more effective cost-efficacy strategy of digoxin serum monitoring as an indispensable tool and cornerstone of clinical decision-making.