Use of digoxin assays in a teaching hospital

Abstract

This study was designed to determine the way in which plasma digoxin assays were used in a large teaching hospital. Clinical staff were interviewed 48 h after the report left the laboratory and were asked the indication for the investigation, their predicted outcome, whether the report had been sighted, how the level of digoxin was interpreted and any change in the management of the patient. Two hundred and eight assays were performed in the 4 wk of the study. Twenty-one inadequate responses and 15 assays performed for other hospitals were not included in the survey. 91% of requests were on inpatients. The majority of requests (81 %) were originated by residents. Suspected toxicity or underdosage were suspected in 36% and 35% or requests respectively. When the requesting doctor was confident of his clinical judgement, he was more likely to be correct if the patient was toxic. The clinical impression of underdosage was often not substantiated. However, 27% of patients in this study had subtherapeutic levels compared with the 12.5% in a study from Melbourne.1 It may be that there is a large number of patients taking digoxin, who have subtherapeutic levels and who would not suffer if the drug were ceased. Of 47 patients whose results were interpreted as toxic only 19 had plasma digoxin levels above 2.0 μg/1 whereas 49 were said to be underdosed when 66 patients had levels less than 1.0 μg/1. Of the 56 patients who had a change in dose only 17 had a follow-up assay performed. The percentage of assays which led to a management change (38%) is much greater than that (12%,) following the performance of serum protein electrophoresis.2 This may reflect the better understanding our medical graduates have of clinical pharmacology than of chemical pathology. This study was designed to determine the way in which plasma digoxin assays were used in a large teaching hospital. Clinical staff were interviewed 48 h after the report left the laboratory and were asked the indication for the investigation, their predicted outcome, whether the report had been sighted, how the level of digoxin was interpreted and any change in the management of the patient. Two hundred and eight assays were performed in the 4 wk of the study. Twenty-one inadequate responses and 15 assays performed for other hospitals were not included in the survey. 91% of requests were on inpatients. The majority of requests (81 %) were originated by residents. Suspected toxicity or underdosage were suspected in 36% and 35% or requests respectively. When the requesting doctor was confident of his clinical judgement, he was more likely to be correct if the patient was toxic. The clinical impression of underdosage was often not substantiated. However, 27% of patients in this study had subtherapeutic levels compared with the 12.5% in a study from Melbourne.1 It may be that there is a large number of patients taking digoxin, who have subtherapeutic levels and who would not suffer if the drug were ceased. Of 47 patients whose results were interpreted as toxic only 19 had plasma digoxin levels above 2.0 μg/1 whereas 49 were said to be underdosed when 66 patients had levels less than 1.0 μg/1. Of the 56 patients who had a change in dose only 17 had a follow-up assay performed. The percentage of assays which led to a management change (38%) is much greater than that (12%,) following the performance of serum protein electrophoresis.2 This may reflect the better understanding our medical graduates have of clinical pharmacology than of chemical pathology.