Diagnostic Use
Maximum serum levels are reached 1 – 2 hours after an oral dose. The level then falls rapidly for 3 – 5 hours as it is distributed. The serum levels then fall with a half-life of 1.5 – 2 days. Monitoring should therefore be performed on specimens collected at least six hours after the last oral dose.
The quoted therapeutic interval of 0.6-2.0 nmol/L is more for rate control in atrial fibrillation without heart failure. In the use of digoxin for heart failure, plasma digoxin level preferably to be kept below 1.0-1.3nmol/L.
Toxic level: usually >2.6 nmol/L but can occur at level <2.6 nmol/L. Patients with renal dysfunction are especially prone to digoxin toxicity because of the prolonged half-life of the drug. Toxicity is more likely in situations of hypokalaemia and hypercalcaemia even when the digoxin level is within the therapeutic interval.
The irregular rhythm from a toxic level sometimes mimics atrial fibrillation. Measuring the serum level will help decide whether insufficient or excessive digoxin dosage is the underlying problem.
Reference Intervals
Therapeutic range
Atrial fibrillation: 0.6 – 2.0 nmol/L
Heart failure : 0.6 – 1.3 nmol/L
Toxic level: Usually >2.6 nmol/L (But may occur at >1.9nmol/L)
Test Method
Principle: Electrochemiluminescence immunoassay
Analyser: Roche Diagnostics Cobas e801
Reagents: Elecsys DIGO
Limitations / Interference
From Roche cobas Elecsys Digoxin package insert v 6.0
- Samples should not be taken from patients receiving therapy with high biotin doses (i.e. > 5 mg/day) until at least 8 hours following the last biotin administration.
- Spironolactone was identified to cause falsely elevated digoxin values when the concentration exceeds 15 mg/L.
- Digoxin-like immunoreactive substances (DLIS) have been identified in blood from patients with renal failure, liver failure, and pregnant women in their third trimester. Studies have shown that the presence of DLIS in a sample can result in a false elevation of digoxin when assayed by commercially available immunoassays.
- The therapeutic antibody fragments against digitalis (e.g. DigiFab, DigiBind) will interfere with digitalis immunoassay measurements. As a consequence Elecsys Digoxin concentrations may be falsely elevated if measured in the presence of the antidote until the Fab fragments are eliminated from the body.
Uncertainty of Measurement
15% at 0.6 nmol/L
7.5% at 3.4 nmol/L