To determine if the concentration of digoxin in your blood is at a therapeutic level or to detect toxic levels of the drug
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 from a vein in your arm
No special preparation is needed, but timing of sample collection is important. When having your blood drawn, tell the person taking your 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 alleviate 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 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 sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
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. When having your blood drawn, tell the person taking your sample when you took your last dose. You may want to write down the exact time at which you took your dose and when the blood was drawn. This information will be useful if your healthcare provider has any questions about your levels.
How is it used?
A digoxin test is used to monitor the concentration of the drug in the blood. The dose of digoxin prescribed may be adjusted depending on the level measured. A healthcare practitioner may order one or more digoxin tests when a person begins 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 someone's 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 a person is receiving the right amount of digoxin.
Once the dosage level is determined, routine monitoring of digoxin levels, at a frequency determined by the healthcare practitioner, will verify correct dosage.
A digoxin test may be ordered when it is suspected that levels are too low in someone who is taking the medication and has 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 someone experiences a physiologic change that may affect blood levels and effectiveness of digoxin, for example, kidney or thyroid problems, cancer, or stomach or intestinal illness.
What does the test result mean?
For congestive heart failure, the ideal range of levels of digoxin in the blood, known as the therapeutic range, may be between 0.5 and 0.8 ng/mL. Each person's response to medications is different. Many factors, including kidney function and concurrent medications, may be involved. If someone's symptoms do not improve or if the person is experiencing side effects, then the healthcare provider may need to adjust the digoxin dose up or down according to that person's 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, 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 system by the kidneys. When someone has kidney problems, the person's 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.
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?
Your primary care provider may order the test, but a cardiologist may also monitor levels of digoxin in your blood.
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. Many times, the blood sample will be drawn just before the next dose is to be taken.