•  Digoxin Measurement

• Measurement of digoxin in serum for the evaluation and management of patients receiving digoxin or who have ingested digoxin-like compounds (e.g., cardiac glycosides).

• Therapeutic concentration:  0.8-2 ng/mL (1-2.6 nmol/L)
• Toxicity:
• Adults: > 2.5 ng/mL (> 3.2 nmol/L)
• Children: > 3 ng/mL (> 3.8 nmol/L)

• Digitalized patients with hypomagnesemia
• Suspected and known atrial fibrillation in patients receiving digoxin
• Drug level monitoring during digoxin therapy
• Suspected and known atrial tachycardia

• While the official upper limit of the therapeutic range is 2 ng/mL, there is some evidence to suggest that mortality in heart failure is improved at levels of 0.5 ng/mL to 0.8 ng/mL, although others suggest that 1 ng/mL to 2 ng/mL is an appropriate therapeutic range.  The specimen should be obtained 12 hours after a dose of digoxin or just before the next dose is due to be given
• Magnesium deficiency increases the risk of digitalis toxicity and arrhythmias, which may be caused by intracellular potassium depletion.
• Digoxin toxicity is often associated with paroxysmal atrial tachycardia with a variable degree of block and/or atrial fibrillation with complete heart block and a slow, regular, wide QRS complex ventricular escape rhythm.
• Results increased in:
• Hypothyroidism
• Medications that inhibit P-gp (e.g., amiodarone, diltiazem, verapamil)
  
• Older patients
• Renal failure

The Evidence & Mechanism: Amiodarone - Digoxin Drug Interaction Amiodarone use in a patient on stable doses of digoxin can result in significant digoxin toxicity. This is clinically significant and should not be missed. EBM Consult Article:  Click Here

• Results decreased in:
• Hyperparathyroidism
• Pregnancy
• Physical activity prior to testing

• Serum creatinine level
• Serum Magnesium level
• Serum Potassium level

• Canrenoate - false increases or decreases in digoxin levels
• Capromab Pendetide - falsely high digoxin serum levels
• Chan Su - false increases in digoxin concentrations
• Cortisone - false increases in digoxin levels
• Dexamethasone - false increases in digoxin levels
• Digitoxin - false increases in digoxin levels
• Digoxin Immune Fab (Ovine) - false increases in digoxin levels
• Fludrocortisone - false increases in digoxin levels
• Fluorescein - invalid digoxin assay results
• Ginseng, American - false readings in digoxin concentrations
• Ginseng, Chinese - false readings in digoxin concentrations
• Ginseng, Siberian - false readings in digoxin concentrations
• Hydrocortisone - false increases in digoxin levels
• Kyushin - false increases in digoxin concentrations
• Methylprednisolone - false increases in digoxin levels
• Prednisolone - false increases in digoxin levels
• Prednisone - false increases in digoxin levels
• Progesterone - false increases in digoxin levels
• Spironolactone - false increases in digoxin levels
• Tan-Shen - false increases in digoxin concentrations

• Heparin or EDTA tube

• In the outpatient setting, patients should not exercise for at least 1 hour prior to sample collection. 
• Collect venous blood specimen 8 to 12 hours after last dose or prior to next dose.

• Store sample at 2°C to 8°C for up to 24 hours or at -20°C for 1 to 2 weeks.

• None

• Eichhorn EJ et al. Digoxin - new perspective on an old drug. N Engl J Med 2002;347:1394-5.
• LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.