# Cyanosis of lips is a common finding in all EXCEPT:
A. Polycythemia
B. Sickle cell anemia
C. Iron deficiency anemia
D. Congenital heart disease
The correct answer is: C. Iron deficiency Anemia.
In general， cyanosis becomes apparent when, the concentration of reduced hemoglobin in capillary blood exceeds 40 g/L (4 g/dL). It is the absolute，rather than the relative，quantity of reduced hemoglobin that is important in producing cyanosis. Thus, in a patient with severe anemia，the relative quantity of reduced hemoglobin in the venous blood may be very large when considered in relation to the total quantity of hemoglobin in the blood. However, since the concentration of the latter is markedly reduced, the absolute quantity of reduced hemoglobin may still be low, and， therefore， patients with severe anemia and even marked arterial desaturation may not display cyanosis. Conversely， the higher the total hemoglobin content， the greater the tendency toward cyanosis; thus， patients with marked polycythemia tend to be cyanotic at higher levels of Sao， than patients with normal hematocrit values.
CAUSES OF CYANOSIS
Central Cyanosis
1. Decreased arterial oxygen saturation
A. Decreased atmospheric pressure- high altitude
B. Impaired pulmonary function
- Alveolar hypoventilation
- Inhomogeneity in pulmonary ventilation and perfusion (perfusion of hypoventilated alveoli)
- Impaired oxygen diffusion
C. Anatomic shunts
- Certain types of congenital heart disease
- Pulmonary arteriovenous fistulas
- Multiple small intrapulmonary shunts
D. Hemoglobin with low affinity for oxygen
2. Hemoglobin abnormalities
A. Methemoglobinemia-hereditary，acquired
B. Sulfhemoglobinemia-acquired
C. Carboxyhemoglobinemia (not true cyanosis)
Peripheral Cyanosis
A. Reduced cardiac output
B. Cold exposure
C. Redistribution of blood flow from extremities
D. Arterial obstruction
E. Venous obstruction
Ref: Harrison's 19th edition, Page 249
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