Specimen Requirements

Container/Tube:

Preferred: Green-top (lithium heparin) tube

Acceptable: Gold-top serum gel tube, plain red-top tube, or EDTA plasma

Specimen Volume: 4.1 µL plus a dead volume 

Stability: Serum or plasma should be physically separated from cells as soon as possible with a maximum limit of two hours from time of collection.  Separated specimens should be analyzed immediately or kept at 2 – 8°C and analyzed within 24 hours. For longer storage, samples may be frozen at -20°C for up to 1-2 weeks. 

Collection Instructions: To obtain steady state concentrations, levels should be drawn 6 to 8 hours after the daily dose or just prior to next scheduled dose.

Note:

1. Digoxin metabolites, cardiac glycosides, and some synthetic steroid-like medications can interfere in assay of digoxin due to cross-reactivity with digoxin-specific antibody.  In addition, the presence of endogenous Digoxin-Like Immunoreactive Factor in some specimens may interfere due to cross-reactivity with the digoxin-specific antibody. Apparently toxic digoxin levels can occur in patients receiving both digoxin and diuretics due to electrolyte imbalances, not assay cross-reactivity.
2. Human anti-mouse antibodies or other heterophile antibodies may be present in patient specimens. This assay has been specially formulated to minimize the effects of these antibodies, however results from patients known to have these antibodies should be carefully evaluated.
3. Levels may be ordered any time toxicity is suspected.