Digoxin (Free) Substance Concentration in Serum/Plasma
This test measures the amount of free (unbound) digoxin, a medication used to treat certain heart conditions, in your blood.
["Understanding your free digoxin level helps doctors monitor your dose for safety and effectiveness."]
Key facts at a glance
- LOINC
- 32067-1
- Short code
- Digoxin Free SerPl-sCnc
- Synonyms
- Digoxin Free SerPl-sCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0.5
- Ref high
- 2
- Critical range
- — – 4 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your doctor may order this test if you’re taking digoxin to manage heart rhythm issues, heart failure, or other cardiac problems. Free digoxin levels are important because they reflect the portion of the drug that actually reaches your heart tissue, where it works.
What to Expect During the Test
A blood sample will be taken from a vein, usually in your arm. You may feel a slight pinch, but it’s quick. No special preparation is needed unless your doctor instructs otherwise.
How the Results Are Used
Results help your healthcare provider adjust your digoxin dose to avoid toxic levels (which can cause side effects like nausea, irregular heartbeat, or vision changes) while ensuring it remains effective.
Common Side Effects of Digoxin
High free digoxin levels can cause symptoms like vomiting, confusion, or fast/pounding heartbeat. Low levels may mean the drug isn’t working well. Always report any unusual symptoms to your doctor.
Reference range
Therapeutic: 0.5-2.0 ng/mLN/A
No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Free digoxin levels are critical because digoxin is highly protein-bound in the blood. Only the free (unbound) fraction actually affects heart function. Routine monitoring helps prevent toxicity or insufficient therapy, especially in patients with kidney issues or other health conditions that alter drug metabolism.
Short name
Free Digoxin Level
Frequently asked questions
Why do I need this test if I’m already taking digoxin?
What does a ‘free’ digoxin test mean differently than a total digoxin test?
Can I eat or drink anything before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy