Cyanotic congenital heart disease is defined as right-to-left shunting of blood that bypasses the lungs, distinguished diagnostically from other causes of neonatal cyanosis (hematologic, pulmonary, or obstructive cardiac causes) through history, physical exam, and targeted laboratory testing. The hyperoxia test is the key diagnostic principle: after placing an infant in 100% oxygen to maximally saturate hemoglobin, arterial oxygen level stratifies the differential diagnosis—above 200 mmHg makes cardiac disease unlikely (favoring pulmonary etiology), 50–150 mmHg suggests a mixing lesion (right- and left-sided blood mixing before systemic circulation), and below 50 mmHg suggests a two-circuit physiology classic for transposition of the great vessels. This belongs to pediatric cardiology's diagnostic framework for the cyanotic newborn, linking pathophysiologic mechanism (shunt type/degree of mixing) to a quantitative, testable clinical marker.
Cyanotic congenital heart disease is defined as right-to-left shunting of blood that bypasses the lungs, distinguished diagnostically from other causes of neonatal cyanosis (hematologic, pulmonary, o…