Cyanosis

• A. Blue/purple coloration of skin/mucous membranes due to tissues near the skin surface having low oxygen saturation
• B. Redness of the skin due to inflammation
• C. Yellowing of the skin due to bilirubin buildup
• D. Patches of dry, scaly skin

Answer: (A)

Cyanosis is the blue/purple discoloration of the skin and mucous membranes caused by low oxygen saturation in tissues near the surface. This signals that arterial blood is not carrying enough oxygen (hypoxemia) or that circulation is impaired.

There are two forms: central cyanosis, which reflects true low arterial oxygen and shows up on lips and mucous membranes, and peripheral cyanosis, due to slowed blood flow and often seen in the extremities. Clinically, it tends to appear when there is enough deoxygenated hemoglobin—about 5 g/dL or more—that makes the color noticeable.

Redness from inflammation, yellowing from bilirubin buildup, and dry, scaly patches describe other skin changes (erythema, jaundice, and dermatitis/xerosis, respectively) and are not cyanosis.

So the blue/purple color change due to low tissue oxygenation is the hallmark of cyanosis.