What is differential cyanosis and what does it suggest in a full‑term newborn?

Differential Cyanosis in Full-Term Newborns

Differential cyanosis is a clinical finding where oxygen saturation differs between the upper and lower body, and in a full-term newborn it strongly suggests a ductal-dependent cardiac lesion with right-to-left shunting through a patent ductus arteriosus (PDA).

Definition and Clinical Pattern

Differential cyanosis occurs when oxygen saturation in the right hand (preductal) is higher than in the foot (postductal), indicating that deoxygenated blood is shunting from the pulmonary artery through a PDA into the descending aorta while the upper body receives better-oxygenated blood from the ascending aorta. 1

• This pattern requires simultaneous pre- and postductal pulse oximetry measurements to detect, as visual assessment of cyanosis is unreliable. 1
• The presence of differential cyanosis combined with differential blood pressures or pulses between upper and lower extremities mandates immediate prostaglandin E1 infusion until congenital heart disease is ruled out. 1

What It Suggests in a Full-Term Newborn

Primary Cardiac Lesions

The most common causes include:

• Patent ductus arteriosus with pulmonary hypertension causing right-to-left shunting at the ductal level, where elevated pulmonary vascular resistance forces deoxygenated blood from the pulmonary artery through the PDA into the descending aorta. 2
• Coarctation of the aorta or interrupted aortic arch with PDA, where the ductus supplies blood to the lower body while the upper body receives blood proximal to the obstruction. 1
• Persistent pulmonary hypertension of the newborn (PPHN) with PDA and right-to-left ductal shunting. 3

Critical Diagnostic Pitfall

Reverse differential cyanosis (RDC) is the opposite pattern—oxygen saturation is lower in the right hand than in the foot—and represents a distinct diagnostic entity. 2, 4

• RDC occurs in supracardiac total anomalous pulmonary venous connection (TAPVC) where highly saturated superior vena cava blood streams through the right ventricle, pulmonary artery, and PDA to the descending aorta, while desaturated inferior vena cava blood crosses the atrial septal defect to supply the upper body. 4, 3
• RDC is also seen in transposition of the great arteries (TGA) with PDA and elevated pulmonary vascular resistance or with preductal aortic coarctation/interruption. 4, 2
• The presence of RDC requires immediate full cardiac evaluation and should be considered an immediate fail in pulse oximetry screening, particularly when performed within the first 24 hours after birth. 3

Immediate Management Algorithm

1. Document simultaneous right hand and foot oxygen saturations in any cyanotic newborn. 1

2. If differential cyanosis is present (right hand > foot):

   • Start prostaglandin E1 infusion immediately to maintain ductal patency. 1
   • Obtain urgent echocardiography to identify the specific cardiac lesion. 5
   • Assess for coarctation, interrupted arch, or critical pulmonary hypertension. 1

3. If reverse differential cyanosis is present (foot > right hand):

   • Start prostaglandin E1 infusion immediately. 4
   • Obtain urgent echocardiography with specific attention to TAPVC and TGA. 4, 3
   • Consider cardiac catheterization if pulmonary artery pressure is elevated to estimate pulmonary vascular resistance. 2

Additional Diagnostic Considerations

• Cyanosis visible from birth suggests either congenital heart disease or methemoglobinemia, though methemoglobinemia typically presents with uniform central cyanosis rather than differential patterns. 6, 7
• Newborns are particularly susceptible to methemoglobinemia due to 50-60% of adult cytochrome b5 reductase activity and 30-40% fetal hemoglobin composition, but this would not produce differential cyanosis. 7
• The visibility of cyanosis requires at least 5 g/L of deoxygenated hemoglobin, meaning anemic newborns may be severely hypoxemic without visible discoloration. 7