Blood tests to evaluate heart disease

Children may have blood tests to help their doctor evaluate their illness, or to help monitor their health after surgery.

These tests may include:

• Complete blood count. This test measures the size, number, and maturity of different blood cells in the blood. These are red blood cells, white blood cells, and platelets. Red blood cells are important because they carry oxygen through the blood to the organs and cells of the body. If you don't have enough red blood cells to carry the oxygen your body needs, you may have anemia. White blood cells multiply when your child has inflammation or an infection. Platelets help the blood clot. This helps stop bleeding from cut, for example. 

• Electrolytes. This test measures minerals in the bloods that are needed for the organ to work as they should. Minerals include sodium, potassium, calcium, and magnesium. If a child is taking water pills (diuretics), the medicine may cause electrolyte problems. Potassium levels are especially important for healthy heart function.

• BNP. This test measures how much BNP hormone is in your child’s blood. BNP stands for B-type natriuretic peptide. The heart’s pumping chambers (ventricles) make BNP. When the heart is working well, there are low levels of BNP in the blood. When the heart has to pump harder than usual, BNP levels are higher. BNP testing can tell if your child has a problem with the heart or lungs. 

• Total protein and albumin. These tests can help assess a child's nutrition and how well the liver is working.

• Prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR).   These look at how well the blood clots. Sometimes these tests are done to assess how well blood-thinning medicines (anticoagulants) are working, or to see if there is a risk of bleeding. These medicines are taken for various heart problems.

• Blood gas. A blood sample is taken from an artery to measure the amounts of oxygen and carbon dioxide in the blood.  The acidity (pH) of the blood is also measured. This test may be done after a pulse oximetry. This is a painless, noninvasive test. It measures the amount of oxygen in the blood through a small, infrared sensor placed on a child's finger, toe, or earlobe.

• Genetic blood tests. These tests may be used to find chromosome problems linked to congenital heart defects. These lab tests must be sent to a special genetics lab. It often take days or weeks before results are available.