Displacement of the set point in the hypothalamus is most commonly caused by pyrogens, which are substances produced by bacteria or immune cells during infection. Pyrogens induce the production of prostaglandin E2 (PGE2) in the hypothalamus, leading to an upward shift in the body's temperature set point. This results in fever, a controlled rise in body temperature that enhances immune function and inhibits pathogen growth. Other options like electrolyte imbalance, dehydration, and hypoglycemia do not directly alter the hypothalamic temperature set point but can affect thermoregulation indirectly.

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