Minimum concentration of reduced hemoglobin required for cyanosis is: (PGI Nov 2009)

Ans: C (5 gm/dl) "In general, cyanosis becomes apparent when the concentration of reduced hemoglobin in capillary blood exceeds 40g/L (4 g/dL) Harrison 19thf248-49, 17th/230"Cyanosis is due to increased amount of reduced Hb (>5mg%]i' in capillary blood'-fy.Afefrta 15th/15CyanosisCyanosis refers to a bluish color of the skin and mucous membranes resulting from an increased quantity of reduced hemoglobin, or of hemoglobin derivatives, in the small blood vessels of those areas. It is usually most marked in the lips, nail beds, ears, and malar eminences.The degree of cyanosis is modified by the color of the cutaneous pigment and the thickness of the skin, as well as by the state of the cutaneous capillaries.. In some instances, central cyanosis can be detected reliably when the Sa02 has fallen to 85%; in others, particularly in dark-skinned persons, it may not be detected until it has declined to 75%.The increase in the quantity of reduced hemoglobin in the mucocutaneous vessels that produces cyanosis may be brought about either by an increase in the quantity of venous blood as a result of dilation of the venules and venous ends of the capillaries or by a reduction in the Sa ., in the capillary blood.In sulhaemoglobmemia cyanosis occurs when its level exceed 0.5gm/dlA methemogiobm level of 15% (i.e.,1.5gm/dl)'3 is associated with visible cyanosis^-Neison iath/2033