Children may have blood tests to help their doctor evaluate their illness, or to help monitor their health after surgery.
These tests may include the following:
Complete blood count. A measurement of size, number, and maturity of different blood cells in the blood. Red blood cells are important because they carry oxygen through the bloodstream to the organs and cells of the body. You are considered anemic if you don't have enough red blood cells. White blood cells multiply when inflammation or infection is present. Platelets help the blood clot.
Electrolytes. Minerals in the bloodstream, such as sodium, potassium, calcium, and magnesium (that are important for the proper function of organs) may be measured. Sometimes, if a child is taking diuretics ("water pills" to help remove extra fluid from the body) for heart disease, the medication may cause electrolyte abnormalities.
Total protein and albumin. These tests can help evaluate a child's nutritional status and liver function.
Prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR). These test the ability of the blood to clot. Sometimes these tests are done to evaluate the effectiveness of anticoagulant drugs (also known as blood thinners) taken for various heart problems or see if there is a risk for bleeding.
Blood gas. A blood sample taken from an artery that measures the amounts of oxygen and carbon dioxide in the bloodstream, as well as the acidity or pH of the blood. A related test, usually done prior to the blood gas, is pulse oximetry. This painless, noninvasive test 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. Tests such as DNA, extended chromosome banding, and fluorescent in situ hybridization (FISH) may be used to detect chromosomal abnormalities associated with congenital heart defects. These lab tests must be sent to a special genetics lab and often take days or weeks before results are available.