To the Editor.—
Avissar et al have described in the Archives a new fluorometric assay for serum digoxin, an assay which they claim to be sensitive to as little as 0.2 ng/ml of serum (135:1029-1032, 1975). Their method involves the addition of 2 ml of serum to 2 ml of 15% (w/v) trichloracetic acid, incubation (two minutes), centrifugation (3,000 rpm for five minutes), and measurement of the resultant fluorescence in the supernatant using a fluorometer with primary and secondary filters of 405 to 436 and 430 to 470 nm, respectively. To our knowledge, theirs is the first description of an apparently simple fluorometric assay in which detection of serum digoxin concentrations of less than 20 ng/ml is claimed. The authors give no details of calibration curves, precision, sensitivity, or reproducibility pertinent to their assay.Cardiac glycosides do not possess any natural fluorescence. They absorb electromagnetic radiation at about 217 nm,
Aronson JK, Boutagy JS, Britten AZ. Fluorometric Assay of Digoxin. Arch Intern Med. 1977;137(7):966. doi:10.1001/archinte.1977.03630190106035
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