Use and misuse of a digoxin assay service.

In a study of the use of a digoxin assay service and its influence on clinical management 285 assay requests were audited over 12 weeks. For 67 (24%) there was no clear clinical indication for the request and for 140 the period between the last dose of digoxin being given and the blood sample being taken was either unknown or inappropriate. Treatment in 64 patients (22%) was changed after the assay result was received [corrected]. 24 of these changes bore no relation to the original clinical indication for requesting the assay, suggesting that such changes were based on the assay result alone. Of samples collected within six hours after the last dose, 15 of 69 (22%) led to a reduction in treatment compared with 10 of 116 (9%) taken after six hours (p less than 0.025), thereby highlighting the danger that incorrectly timed samples may lead to inappropriate clinical decisions.