To determine if the concentration of digoxin in your blood is at a therapeutic level or to detect toxic levels of the drug in your blood
After the start of digoxin therapy and at regular intervals to ensure that drug levels are within therapeutic range (not too low or too high as to be toxic)
A blood sample drawn by a needle from a vein
No special preparation is needed, but timing of sample collection is important, and you may be instructed to have your blood drawn a specific number of hours after your last dose of digoxin, typically 6-8 hours. When having your blood drawn, tell the person collecting your blood sample when you took your last dose of digoxin.
Digoxin is a drug used to treat heart failure and abnormal heart rhythms. Heart failure, including congestive heart failure (CHF), causes the heart to become less effective at circulating blood. As a result, blood backs up into the legs, hands, feet, lungs and liver, causing swelling, shortness of breath, and fatigue. This test measures the amount of digoxin in the blood.
Digoxin is prescribed to relieve some symptoms of heart failure. It strengthens the contractions of the heart and helps it to pump blood more efficiently. Digoxin also helps control the heart rate and abnormal heart rhythms known as arrhythmias. It will not cure heart failure or arrhythmias, which are long-term (chronic) conditions, but can help to manage the symptoms along with diet, exercise, and other medications.
Digoxin levels must be monitored because the drug has a narrow safety range. If the level in the blood is too low, symptoms may recur. If the level is too high, toxicity may occur. Digoxin dosage may be adjusted based on levels measured.
How is the test used?
A digoxin test is used to monitor the drug level in the blood. The dose of digoxin prescribed may be adjusted depending on the level measured. Your healthcare practitioner may order one or more digoxin tests when you begin treatment to determine if the initial dosage is within therapeutic range and then order it at regular intervals to ensure that the therapeutic level is maintained. A digoxin test may also be used to determine if symptoms are due to an insufficient amount of the drug or to digoxin toxicity.
When is it ordered?
A healthcare practitioner will order the test to measure digoxin at the beginning of drug therapy to ensure correct dosage. Digoxin takes approximately one to two weeks to reach a steady level in the blood and in the target organ, the heart. A test done at that time will reflect more accurately whether you are receiving the right amount of digoxin.
Once the dose is determined, routine monitoring of digoxin levels, at a frequency determined by your healthcare practitioner, will verify correct dosage.
A digoxin test may be ordered when it is suspected that levels are too low if you are taking the medication and have symptoms of heart failure, such as:
- Shortness of breath
- Swelling in the hands and feet (edema)
- Blurred vision or seeing yellow or green halos
- Irregular heartbeat
- Difficulty breathing
- Loss of appetite
Changes in health status can affect levels of digoxin and its ability to control symptoms. Digoxin tests may be done, and the dose adjusted if necessary, when you have conditions that may affect blood levels and effectiveness of digoxin, such as kidney or thyroid problems, cancer, or stomach or intestinal illness.
What does the test result mean?
For congestive heart failure, the therapeutic range may be between 0.5 and 0.8 nanograms/milliliter (ng/mL). Each person's response to medications is different. Many factors, including kidney function and use of other medications, may be involved. If your symptoms do not improve or if you experience side effects, then your healthcare provider may need to adjust the digoxin dose up or down according to your needs.
Is there anything else I should know?
When prescribed digoxin, you should discuss with your healthcare provider and pharmacist all other prescription and over-the-counter medications, dietary supplements, and herbal remedies you are taking. These can affect the level of digoxin in the blood and its effectiveness. Be sure to notify your healthcare provider about any changes in use of these products while you are taking digoxin.
Prescription drugs that can interact with digoxin include: quinidine, flecainide, verapamil, amiodarone, amiodarone, azole antifungals (such as itraconazole, ketoconazole), cyclosporine, lapatinib, macrolide antibiotics (such as clarithromycin, erythromycin), propafenone, ranolazine, rifampin, eliglustat and ciprofloxacin. Herbal remedies such as St. John's wort, oleander, and lily of the valley may affect levels of digoxin in the blood. Eating licorice may also affect blood levels of the drug.
Digoxin is primarily cleared from the body by the kidneys. If you have kidney problems, your healthcare provider may want to monitor kidney function and blood potassium levels since kidney dysfunction and low levels of potassium can result in symptoms of digoxin toxicity.
People with a certain type of irregular heartbeat called atrial fibrillation are advised not to take digoxin as it may increase their risk of dying.
In cases where toxic levels of digoxin are found, a healthcare practitioner may administer a specialized antidote (digoxin immune FAB) to reverse the effects of the digoxin.
How long will I need to be on digoxin?
Digoxin is prescribed to treat heart failure, a long-term, chronic condition. It will not cure heart failure but will help to control it. You may have to take digoxin — and have tests to monitor its level in the blood — for the rest of your life.
Who orders digoxin tests?
Why is it important to have my blood drawn for my digoxin test at a certain time?
Timing of the digoxin blood test is important because if the sample is drawn too soon after a dose, the results of the test may be erroneously high and will show a toxic level when that is not the case. Typically, a blood sample should be drawn 6-8 hours after a dose. Many times, the blood sample will be drawn just before the next dose is to be taken.