Department of Laboratory Medicine
University of Washington
 
Clinical assay interference and limitations

Digoxin [DIG]

Interferences

A number of interferences are known for digoxin immunoassays, including the AxSym digoxin immunoassay used at the University of Washington and Harborview Medical Centers:

Pregnant women, newborns and persons with renal or hepatic insufficiency may accumulate endogenously produced digoxin-like immunoreactive substances (DLIS) that lead to falsely increased measurements. Accumulation of cross-reactive digoxin metabolites in renal failure may also result in further false increases in measured digoxin concentrations.

Patients taking spironolactone may have falsely decreased digoxin levels when measured by the AxSym method.

Measurements made with AxSym reagents on specimens from patients who have been treated with the digoxin antidotes, Digibind or Digifab, will approximately reflect the pharmacologically active free drug concentration and may be useful in monitoring such treatment.

Some patients may have human antimouse antibodies (HAMA), particularly those who have been treated with therapeutic monoclonal antibody preparations. HAMA may interfere in unpredictable ways with immunoassays based on mouse antibodies, including the AxSym digoxin immunoassay.

Cardioactive glycosides related to digoxin may be found in some plants and in toad venom. These substances, and alternative medications derived from them (for example, the Chinese traditional medicine, Chan Su), will cross-react in digoxin assays. A positive result may help to confirm the presence of one of these substances, but apparent digoxin concentrations have not been correlated with extent of toxicity.

For questions about the interpretation of digoxin measurements, please contact the Laboratory Medicine Resident on call (206-598-6190).




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Created: March 27, 2002
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