Laboratory tests for heart failure
Routine lab blood tests are important in the evaluation of people with heart failure. These tests can help identify causes of heart failure, such as hypothyroidism; whether other organs, such as the kidneys and liver, have been affected by the heart failure; or whether medicines, such as diuretics, have affected the normal electrolyte levels, such as sodium or potassium levels. The following lab tests are commonly done in people with signs or symptoms of heart failure.
A reduced red blood cell count (anemia) may mean that heart failure is caused or aggravated by a decrease in the oxygen-carrying capacity of the blood. A very low blood count may be a sign that anemia is a contributing factor that is making your heart failure worse. Even if this is not the case, a low blood count can make your heart work harder and can be dangerous if you have severe heart failure. Knowing the white blood cell count can be helpful because an elevated white count often indicates that you have an infection, which places additional stress on your heart.
This test measures the level of a substance in the blood called creatinine. The creatine level can help determine how well the kidneys are working. Creatinine is excreted in the urine. High levels of creatinine may indicate that a kidney problem is responsible for fluid buildup in the body, not heart failure.
A blood urea nitrogen (BUN) test measures the amount of nitrogen in the blood that comes from urea. A BUN test helps estimate how well the kidneys are functioning. Severe heart failure can decrease kidney function. Several common heart failure medicines—particularly diuretics and angiotensin-converting enzyme (ACE) inhibitors—can also decrease kidney function.
A brain natriuretic peptide (BNP) test measures the amount of the BNP hormone in your blood. BNP is made by your heart and tells how well your heart is working. Normally, only a low amount of BNP is found in your blood. However, if your heart has to work harder over a long period of time, such as from heart failure, the heart releases more BNP and the blood level of BNP will get higher. The BNP level may drop when treatment for heart failure is working.
Albumin is a protein in the body. Decreased levels of this protein may indicate that fluid buildup in the body is caused by an intestinal disorder (hypoalbuminemia), a liver problem, or kidney disease.
Thyroid hormone measurements may be needed if you have a rapid, irregular heartbeat (atrial fibrillation), have evidence of thyroid disease, or are older than 65. Abnormal findings may be a sign that heart failure is caused or made worse by an underactive thyroid (hypothyroidism) or an overactive thyroid (hyperthyroidism).
Protein or red blood cells in the urine may indicate a kidney disorder.
Fasting blood glucose
A fasting blood glucose test measures the amount of glucose in your blood after you have not eaten for at least 8 hours. Glucose is a natural sugar in the body that is used for energy. High levels of glucose in the blood may indicate diabetes.
A lipid panel is a blood test that measures lipids—fats and fatty substances used as a source of energy in your body. Lipids include cholesterol, triglycerides, high-density lipoprotein (HDL), and low-density lipoprotein (LDL).
Liver function tests (SGOT, SGPT)
Liver function tests include a variety of tests that measure certain enzymes and other substances produced by the liver. If the levels of these substances are high, it may indicate damage or disease in the liver. Heart failure may also cause fluid buildup in the liver, which also may cause elevated liver function test results. For more information, see the medical tests Alanine Aminotransferase, Alkaline Phosphatase, and Aspartate Aminotransferase.
People with heart failure need to maintain the concentration of electrolytes in the blood (particularly sodium, potassium, and magnesium). This is especially true for people who take diuretics, which can lower sodium, magnesium, or potassium levels in the blood if the dose is too high. Other medicines such as ACE inhibitors, by contrast, can cause high potassium levels.
Your electrolytes should be checked regularly, particularly if your symptoms are changing or if your medicines are being adjusted.
Prothrombin time (PT)/partial thromboplastin time (PTT)
PT/PTT measures how long it takes for your blood to clot. If you need to take warfarin (a blood thinner) because you are at risk for stroke, you will need to monitor your PT regularly to make sure that you are taking the correct dose of warfarin. A method of standardizing prothrombin time results, called the international normalized ratio (INR) system, is used to compare prothrombin time results among labs using different test methods. Using the INR system, treatment to prevent blood clots (anticoagulant therapy) remains consistent even if a person has the test done at different labs.
If you are a sexually active woman of childbearing age and have new symptoms of heart failure, your doctor may order a pregnancy test. Pregnancy can occasionally cause heart failure, and pregnancy and childbirth may be dangerous for a woman with severe heart failure, particularly if the heart failure is caused by mitral valve stenosis or other obstructive heart disease.