Which substance is used to measure extracellular fluid volume by the indicator-dilution principle?

• A Inulin ✓
• B Evans blue dye
• C Deuterium oxide
• D Technetium-labeled red cells

Explanation

Inulin crosses capillary membranes freely but does not enter cells, so it equilibrates throughout the extracellular fluid and measures ECF volume. Deuterium oxide measures total body water, Evans blue binds albumin and measures plasma volume, and labeled red cells measure red cell or blood volume. Mannitol and sucrose are alternative ECF markers used for the same purpose.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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