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Blood Test Tracker

Digoxin

Measures digoxin (Lanoxin), a heart medicine, in your blood to check that the dose is in a helpful and safe range.

AI-verified against cited sources. Awaiting expert reviewLOINC 10535-3

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What it is

Digoxin is a heart medicine used for heart failure and to control the heart rate in atrial fibrillation. It has a narrow safety margin, which means the helpful dose and the harmful dose are close together. This test shows how much digoxin is in your blood. To be useful, the sample should be drawn just before your next dose or at least 6 hours after the last one.

Why it matters

Too little digoxin may not help your heart. Too much can cause nausea, vision changes, confusion and a slow or irregular heartbeat. The level is only one clue. Your symptoms, heart rhythm, kidney function and potassium matter just as much, and the FDA label says one level alone should not be the basis for raising or lowering the dose.

If it’s low

A level below 0.5 ng/mL means less digoxin in your blood than the range where benefit has been shown. For some people a lower target is intended, and for others it can mean doses are being missed or not absorbed.

Common causes

  • Missed or irregular doses
  • A sample drawn long after the last dose, since levels can be 10% to 25% lower at 24 hours than at 8 hours on a once-daily schedule
  • Improved kidney function, which clears the drug faster
  • Reduced absorption from conditions such as chronic diarrhea or other malabsorption
  • Hyperthyroidism, which has been linked to lower levels

What can help

  • Ask your clinician or pharmacist about a daily routine that keeps dose timing consistent, and use reminders
  • Ask your clinician or pharmacist about the best timing around other medicines and supplements
  • Tell your clinician about missed doses or ongoing diarrhea

If it’s high

A level above about 2 ng/mL is linked to more side effects with no added benefit, and even levels above about 1.2 ng/mL carry a somewhat higher chance of side effects, especially when potassium is low. A high level does not always mean you feel unwell, and your clinician will weigh it with your symptoms and heart rhythm.

Common causes

  • A sample drawn too soon after a dose, when the level is briefly high
  • Reduced kidney function, since digoxin leaves the body mostly through the kidneys
  • Older age or low body weight
  • Medicines that raise digoxin levels, such as amiodarone, verapamil and clarithromycin
  • Digoxin-like substances or certain herbal products that some tests read as digoxin
  • Extra doses taken by mistake

What can help

  • Tell your clinician right away about nausea, vomiting, loss of appetite, blurred or yellow-green vision, a very slow or irregular pulse, or confusion
  • Make sure your clinician and pharmacist know about every medicine and supplement you take, including herbal products
  • Ask whether potassium, magnesium and kidney function should be checked along with this test

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0.5–2 ng/mL. Source: U.S. FDA label via NLM DailyMed (Hikma Pharmaceuticals), Frontiers in Cardiovascular Medicine.

Wellness targets

Narrower ranges some clinicians aim for. Being outside one doesn’t mean something is wrong.

0.5–0.9 ng/mL (Adults). Evidence: Limited. In a post hoc analysis of the DIG heart failure trial (Ahmed 2006), people with levels of 0.5 to 0.9 ng/mL had fewer deaths and hospital stays than people on placebo, while higher levels brought no extra survival benefit. The analysis was not randomized by level and applies to heart failure, not other uses of digoxin.

FDA digoxin label concentration thresholds (band labels are our wording)

  • Less benefit seenbelow 0.5 ng/mL
  • Benefit seen, lower chance of side effects0.5 to under 1.2 ng/mL
  • More side effects possible1.2 to under 2 ng/mL
  • More toxicity without added benefit2 and above ng/mL

What can affect your result

  • Time since the last dose: draw just before the next dose, or at least 6 hours after the last
  • Kidney function and age
  • Potassium, magnesium and calcium levels, which change how sensitive the heart is to digoxin
  • Thyroid function
  • Interacting medicines, including some that change how the body pumps digoxin out
  • Digoxin-like substances in newborns, pregnancy, and kidney or liver disease, and certain herbal products
  • Assay method: LC-MS/MS is less affected by interfering substances than standard immunoassays
  • A sample drawn within 6 to 8 hours of a dose reads high because the drug is still spreading into tissues.
  • Digoxin-like substances in the blood can make some tests read falsely high. They are found in many newborns and in some people who are pregnant or have kidney or liver disease.
  • Spironolactone, canrenone and some herbal products (for example Siberian ginseng, Asian ginseng, ashwagandha and Chan Su) can be detected as digoxin by some assays.
  • After treatment with digoxin immune Fab, standard immunoassay results are unreliable.

Just before the next scheduled dose, or at least 6 hours after the last dose, per the drug label. The adult half-life is typically 36 to 48 hours, so a steady level takes about 1 to 3 weeks to settle after a dose change, longer with poor kidney function.

When to talk to a clinician

Contact your clinician the same day for nausea, vomiting, new loss of appetite, blurred or yellow-green vision, confusion, or a pulse that is much slower than usual. A level above 2 ng/mL should be reviewed by your prescriber. Call 911 or your local emergency number for fainting, chest pain, trouble breathing or a very slow heartbeat with dizziness.

Questions you could ask

  • What level are you aiming for in my case?
  • How long after my dose should my blood be drawn?
  • Could one of my other medicines or supplements be raising my digoxin level?
  • Should we check my potassium, magnesium and kidney function?
  • Could missed doses or poor absorption explain this level?
  • Is this level a problem for me, given how my heart is doing?

Questions people ask

Why must the blood be drawn so long after my dose?

For the first 6 to 8 hours after a dose, digoxin is still spreading from the blood into tissues, so blood levels run higher than the amount at the heart. The label says to sample just before the next dose or at least 6 hours after the last one.

Is a higher digoxin level better?

Not necessarily. In a large heart failure trial analysis, levels of 0.5 to 0.9 ng/mL were linked to fewer deaths, while higher levels showed no extra survival benefit. The best level depends on why you take digoxin, and your clinician sets your target.

Can supplements change my result?

Some herbal products, such as Siberian ginseng, Asian ginseng, ashwagandha and Chan Su, can make some tests read as if digoxin were present. Tell your clinician and the lab about everything you take.

Show the science and sources

Units

  • 1 ng/mL = 1 ng/mL
  • 1 ng/mL = 1.281 nmol/L

Open the Digoxin unit converter

For clinicians and researchers

Digoxin inhibits Na+/K+-ATPase and has a narrow therapeutic index. Following a dose there is a 6 to 8 hour tissue distribution phase during which serum concentrations do not reflect the myocardial site of action, so the FDA label directs sampling just before the next dose or at least 6 hours after the last dose, and notes concentrations are 10% to 25% lower at 24 than at 8 hours on once-daily dosing. The adult half-life is typically 36 to 48 hours (longer in renal impairment, 3.5 to 5 days in anuria), with steady state in 1 to 3 weeks. About 50% to 70% is excreted unchanged in urine in proportion to GFR, and P-glycoprotein inducers and inhibitors alter exposure. Toxicity is increased by hypokalemia, hypomagnesemia and hypercalcemia. The label cites diminished efficacy below 0.5 ng/mL and increased toxicity without benefit above 2 ng/mL, with a rising potential for adverse events above 1.2 ng/mL, enhanced by low potassium. In the post hoc DIG trial analysis (Ahmed 2006), levels of 0.5 to 0.9 ng/mL were associated with lower mortality and hospitalization versus placebo, while 1.0 ng/mL or higher lowered heart failure hospitalization without an effect on mortality. Digoxin-like immunoreactive substances (DLIS) are present in up to half of neonates and in some pregnant, renal or hepatic patients, usually at 0.2 to 0.4 ng/mL as digoxin equivalents; spironolactone, canrenone and some herbal products can also cross-react, ultrafiltrate free digoxin is about 25% lower than total, and LC-MS/MS methods are less susceptible. After digoxin immune Fab (DigiFab) treatment, immunoassay results are clinically misleading until the Fab fragments clear, which can take days to a week or more in kidney failure (DigiFab label). Lab practice varies: the traditional 0.8 to 2.0 ng/mL range dates from the 1970s, a 2023 review reports that 4 of 10 national labs have lowered the upper limit to 0.9 to 1.2, and the 2013 ACCF/AHA heart failure guideline (as reported in that review) suggests 0.5 to 0.9. Conversion: 1 ng/mL = 1.28 nmol/L.

LOINC 10535-3 (primary), 14698-5, 83093-5. Specimen: serum-or-plasma.

Sources

  1. Digoxin prescribing information (Dosage and Administration 2.2, Drug Interactions 7.4, Overdosage, Clinical Pharmacology), U.S. FDA label via NLM DailyMed (Hikma Pharmaceuticals) (2025)
  2. Digoxin and reduction in mortality and hospitalization in heart failure: a comprehensive post hoc analysis of the DIG trial, European Heart Journal (2006)
  3. Review: Failure of current digoxin monitoring for toxicity: new monitoring recommendations to maintain therapeutic levels for efficacy, Frontiers in Cardiovascular Medicine (2023)
  4. Digoxin (PubChem CID 2724385), PubChem, National Library of Medicine
  5. DigiFab (digoxin immune fab) prescribing information (Warnings and Precautions: Laboratory Tests), U.S. FDA label via NLM DailyMed (BTG International) (2026)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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