Digoxin
Label Mnemonic: DIG
Epic Lab Code: LAB23
Downtime Form: A-1a Therapeutic Drug Assay Requisition
Chemistry
6240 RCP
356-3527
Specimen(s):
Plasma
Collection Medium:
Plasma Separator Tube 4.5 mL
Alternate Collection Media:
Call laboratory for additional acceptable specimen collection containers.
Minimum:
3 mL whole blood in light green top tube or TWO Microtainer® devices.
Testing Schedule:
24 hrs/day, 7 days a week, including holidays.
Turn Around Time:
1 hour (upon receipt in laboratory)
Reference Range:
Therapeutic: <2.0 ng/mL for trough levels (see comments)

Critical value: >2.0 ng/mL (adults)
Comments:
This assay measures both bound and free digoxin, so elevated values will be found in patients undergoing treatment with digoxin antidote therapy (e.g., DigiFab or Digibind antibody fragments).

The general therapeutic range for digoxin is 0.5-2.0 ng/mL. However, the optimal therapeutic range for a given patient may differ based on factors such as patient age and indication for therapy. American College of Cardiology Foundation (ACCF) / American Heart Association (AHA) 2013 guidelines recommend therapeutic digoxin plasma levels of 0.5-0.9 ng/mL for management of heart failure (1). For treatment of atrial fibrillation, digoxin plasma levels up to 2 ng/mL may be necessary to achieve better ventricular rate control. Pediatric reference ranges have not been established.

Digoxin has a narrow therapeutic window, and plasma concentrations greater than 2 ng/mL confer high risk of adverse effects. Elderly patients are more susceptible to adverse effects and more likely to show toxicity even at plasma levels of 1.4-2.0 ng/mL.
Test Limitations:
The assay is unaffected by icterus (bilirubin is less than 66 mg/dL), hemolysis (Hb is less than 1000 mg/dL), lipemia (Intralipid is less than 1500 mg/dL), and biotin (less than 100 ng/mL) (criterion: recovery within plus or minus 0.08 ng/mL if digoxin is less than 0.8 ng/mL, or within plus or minus 10% if digoxin levels are greater than 0.8 ng/mL). No interference was observed from rheumatoid factors up to a concentration of 1630 IU/mL).In patients receiving therapy with high biotin doses (i.e. is greater than 5 mg/day) no sample should be taken until at least 8 hours after the last biotin administration.

Uzara, nabumetone, hydrocortisone, canrenone and pentoxifylline cause falsely elevated digoxin results at concentrations of the recommended daily dose. Spironolactone causes elevated digoxin results above drug levels of 10,000 ng/mL. Digoxin-like immunoreactive substances (DLIS) have been identified in blood from patients in renal failure, liver failure, and pregnant women in their third trimester. DLIS can lead to false elevation of digoxin when measured by immunoassays.

References:
(1) 2013 ACCF/AHA Guideline for the Management of Heart Failure: Executive Summary. A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2013;62(16):1495-1539

(2) Valdiva R, Hornig Y, Gross S, Khayam-Bashi H: Digoxin-like Immunoreactive Factor Cross-reactivity in the CEDIA Digoxin R Assay on the RA-1000. Clin. Chem. 1990;36(6):1111
Methodology:
Competition Principle

Assay methodology updated on 5/23/17
CPT Code:
80162
 
See Additional Information:
Chemistry Critical Lab Values