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Objective To determine what triggers the use of digoxin therapeutic drug monitoring (TDM) that adheres to established indications and the change in digoxin dosage after the result of monitoring is obtained. Methods This prospective study included 86 patients admitted to 6 medicine wards and 2 intensive cardiac care unit wards in a tertiary-care center. Data on patients' demographics, drug therapy, serum chemistry values, indications for digoxin therapy, indications for ordering the drug assay, timing of the blood sample relative to administration of the last dose, and physicians' decisions after attaining serum digoxin concentrations were collected. Results Eighty-six digoxin assays were evaluated. Indications for the use of a digoxin assay were mostly routine without a clear indication (66%); in only 22% of the assays were orders considered clinically justified. Eleven patients had concentrations >2 ng/mL, but only 8 patients had digoxin intoxication. In only 31% of patients did the medical staff respond to the results. In only 21% of patients with subtherapeutic drug concentrations was there a change in digoxin dose. Conclusions Although there are clear indications for the use of digoxin TDM, physicians seem to routinely order these blood tests. The clinicians did not adequately use the digoxin concentration data to optimize therapy. The assistance of a clinical pharmacist or pharmacologist is warranted for use of the assays, to optimize digoxin therapy.

“Outcomes Assessment” has become one of the enduring buzzwords of the decade. But it often seems to be like the weather: Everyone talks about it, but relatively few do anything about it. As clinical laboratory scientists, we have repeatedly challenged ourselves to demonstrate that laboratory results affect patient outcome. Yet very few well-done studies have been published. (How many times have you heard and read the results of those few studies by now?) One difficulty is the universal use of laboratory testing. Would it be acceptable to deny laboratory testing to a control group? The field of point-of-care testing (POCT) offers a major opportunity, because there are many tests not yet in widespread use. This allows ethical comparisons to be designed. (Imagine presenting to the Human Investigation Committee a study of the benefit of digoxin monitoring using a control group in which no digoxin measurements were allowed. Would they approve it? Such a study was done when digoxin assays were just being introduced and convincingly demonstrated a 50% reduction in clinical digitalis toxicity in monitored patients (1).) Another barrier is the tendency to focus on medical outcomes: decreased mortality or morbidity, shorter length of stay, decreased readmission rate, improved quality of life, etc. Medical interventions may directly alter medical outcomes, but laboratory tests do not. The effect of a test result is always filtered through the change in medical management it engenders. The ability to link the test result to the outcome requires a good correlation between the result and the therapeutic intervention. The size and duration of studies needed to establish the effectiveness of medical interventions are well known. How much larger and longer must a study be to average out the additional variation in the test itself and in the linkage between result and intervention? (Despite such …

The digoxin therapeutic drug monitoring service was evaluated during a 7-week period at Leeds General Infirmary. Data were collected for 88 patients who had one or more assays performed. The requesting clinician was contacted for each assay, and a questionnaire completed. Results were assessed to determine the appropriateness of the assay request and the action taken following receipt of the result. During the assessment period, 113 serum digoxin assays were requested. Data were collected for 88 (78%) of these, of which 22 (25%) were considered to have met all the criteria for an appropriate assay request and subsequent action. A total of 66 (75%) serum digoxin assays were assessed as wasted. The digoxin therapeutic drug monitoring service is used inappropriately at Leeds General Infirmary.