What this test measures
Quantitative serum digoxin — a cardiac glycoside used for rate control in atrial fibrillation and as add-on therapy in heart failure with reduced ejection fraction. Steady-state is achieved 7–10 days after starting or changing dose. Sample 6–24 hours after the last dose (typically morning before next dose) for trough level. Earlier sampling captures the distribution peak and over-estimates true tissue levels.
Why it matters
Digoxin remains widely used in India for AF rate control (cheap, oral) and as add-on heart failure therapy. Therapeutic window is narrow (0.5–2.0 ng/mL classical; many cardiologists now target 0.5–0.9 for HF based on DIG trial sub-analyses). Toxicity is common in elderly, renal impairment (digoxin is renally cleared), and hypokalaemia / hypomagnesaemia. Drug interactions are extensive — amiodarone, verapamil, propafenone, quinidine, spironolactone, macrolides, P-glycoprotein inhibitors all raise levels. Toxicity manifests as nausea, anorexia, visual disturbance (yellow-green halos), arrhythmias (any rhythm — pathognomonic is regularised AF, bidirectional VT). Digibind / DigiFab (Fab fragments) is the antidote.
How to prepare
Sample 6–24 hours post-dose (avoid the 2–6 hour distribution phase). For maintenance monitoring, draw immediately before the next dose. Disclose all medications (amiodarone, verapamil, spironolactone, macrolides), renal function (eGFR), electrolytes (K+, Mg2+), and the indication.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Serum Digoxin (ng/mL)[1][2] | Therapeutic 0.5 – 2.0 (HF target 0.5 – 0.9; AF rate control up to 2.0) | < 0.5 ng/mL: sub-therapeutic — review compliance, drug interactions, or under-dosing. | 2.0 – 3.0 ng/mL: above range — toxicity risk increases; reduce dose or interval, check K+ / Mg2+ / renal function. > 3.0: toxic — likely symptomatic; hold drug; correct electrolytes; ECG monitoring; consider Digibind if life-threatening arrhythmia or potassium > 5.5 mEq/L. > 6.0 with acute ingestion: severe — Digibind indicated. |
Digoxin therapeutic and toxic ranges
| Digoxin (ng/mL) | Status | Action |
|---|---|---|
| < 0.5 | Sub-therapeutic | Check compliance, dose, interactions |
| 0.5 – 0.9 | Target for HF | Maintain |
| 0.9 – 2.0 | Target for AF rate control | Maintain; monitor symptoms |
| 2.0 – 3.0 | Above range | Reduce dose; check K+ / Mg2+ / renal |
| > 3.0 | Toxic | Hold drug; ECG; consider Digibind |
| > 6.0 acute | Severe | Digibind indicated |
Frequently asked questions
When should I take my digoxin level?
At least 6 hours after the last dose (preferably 12–24 hours) and at steady state (7–10 days after starting or changing dose). Earlier samples over-estimate true tissue levels and lead to inappropriate dose reductions.
Why is the target lower in heart failure than AF?
DIG trial sub-analyses showed best HF outcomes (and lower mortality) at digoxin levels of 0.5–0.9 ng/mL. AF rate control sometimes needs higher (up to 2.0) — but accept the lowest level that achieves the goal.
What raises my risk of toxicity?
Older age, falling renal function, hypokalaemia, hypomagnesaemia, hypercalcaemia, hypothyroidism (slower clearance), and many drug interactions (amiodarone, verapamil, spironolactone, macrolide antibiotics). Review medications carefully.
I see yellow-green halos around lights — could that be digoxin?
Yes — visual disturbance (yellow-green tint, halos, scotomas) is a classic feature of digoxin toxicity. Get a digoxin level urgently and review the dose.
What is Digibind?
Anti-digoxin Fab antibody fragments that bind and inactivate digoxin. Used for life-threatening arrhythmias, hyperkalaemia (> 5.5 mEq/L), or massive overdose. Effect within 30 minutes.
How long does it take to clear after stopping?
Half-life ~36 hours with normal renal function — clears over 3–5 days. Much longer with renal failure.
Related Drugs / Therapeutic Monitoring tests
Tests commonly ordered alongside DIGOXIN, or that help interpret an unexpected result.
Sources & references
- Mayo Clinic Labs — Digoxin, Serum · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Digoxin Test · accessed 2026-05-30T00:00:00.000Z
- StatPearls — Digoxin Toxicity · accessed 2026-05-30T00:00:00.000Z
- AHA/ESC Heart Failure Guidelines · accessed 2026-05-30T00:00:00.000Z
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