Children may have blood tests to help their doctor evaluate their illness, or to help
monitor their health after surgery.
Complete blood count. This test measures the 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. If you don't have enough red blood cells, you
have anemia. White blood cells multiply when inflammation or infection is present.
Platelets help the blood clot.
Electrolytes. This test measures minerals in the bloods, such as sodium, potassium, calcium, and
magnesium, which are important for the proper function of organs. Sometimes, if a
child is taking diuretics ("water pills"), the medicine may cause electrolyte abnormalities.
Potassium levels are especially important for healthy heart function.
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
how well anticoagulant drugs ( blood thinners such as coumadin) are working, or to
see if there is a risk for 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 or pH of the blood is also measured. This test
may be done after a 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. These tests may be used to detect chromosome 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.