​Children's Heart Center

Blood Tests

Patients with congenital heart disease may have blood tests done to help the evaluate their illness or monitor their health after surgery.

Tests may include:

Complete blood count
A measurement of size, number and maturity of different blood cells in a specific volume of blood. Red blood cells are important because they carry oxygen through the bloodstream to the organs and cells of the body. Having too few red blood cells can make a patient feel tired, and having too many red blood cells may also indicate a problem. For example, patients with cyanotic congenital heart disease may have high numbers of red blood cells in the bloodstream, in an effort by the body to provide enough oxygen to the organs. White blood cells multiply when inflammation or infection is present.

Minerals in the bloodstream, such as sodium, potassium, calcium and magnesium (that are important for the proper function of organs), may be measured. Electrolytes may be out of balance when a patient is taking diuretics.

Total protein and albumin
These tests can help evaluate a patient’s nutritional status.

Prothrombin time (PT), partial thromboplastin time (PTT) and international normalized ratio (INR)
Tests evaluating the effectiveness of anticoagulant drugs (also known as blood thinners) taken for various heart problems, including artificial-valve replacement and irregular heart rhythms.

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.

Pulse oximetry
An oximeter is a small machine that measures the amount of oxygen in the blood. To obtain this measurement, a small sensor (similar to an adhesive bandage) is taped to a finger or toe. When the machine is on, a small red light can be seen in the sensor. The sensor is painless, and the red light does not get hot.