Peripheral Artery Disease (PAD): This condition is characterized by the narrowing or blockage of the arteries outside of the heart, leading to reduced blood flow to the limbs. The symptoms of PAD, such as pain, numbness, and discoloration (including redness due to inflammation or decreased oxygenation), match the presentation of a red foot with arterial blockage.

Deep Vein Thrombosis (DVT): Although DVT primarily affects the venous system, it can lead to inflammation and increased pressure in the affected limb, potentially causing redness and discomfort. The blockage in this context would be more related to venous return rather than arterial supply.
Cellulitis: This is a bacterial skin infection that can cause redness, swelling, and warmth of the skin. While it doesn't directly cause arterial blockage, the infection can lead to significant inflammation and potentially compromise blood flow to the area.
Erythromelalgia: A disorder characterized by burning pain, heat, and redness in the hands and feet. It can be primary or secondary to other conditions like myeloproliferative disorders. The redness and discomfort could be mistaken for signs of arterial blockage.

Acute Limb Ischemia: A sudden decrease in limb perfusion that threatens limb viability. It is a medical emergency requiring immediate attention. The symptoms can include the six Ps: pain, pallor, pulselessness, poikilothermia, paresthesia, and paralysis. Redness might not always be present, but the condition's urgency makes it a "do not miss" diagnosis.
Septic Arthritis or Osteomyelitis: Infections within the joint or bone, respectively. These conditions can cause significant pain, redness, and swelling. While they might not directly cause arterial blockage, they are emergencies that require prompt treatment to prevent serious complications.

Buerger's Disease (Thromboangiitis Obliterans): A rare disease of the arteries and veins in the arms and legs. It leads to blockages that can cause pain, tissue damage, and potentially gangrene. It's more common in young smokers.
Raynaud's Phenomenon: A condition that affects blood flow to the fingers and toes, and sometimes the ears, nose, and lips. It's characterized by a sudden and temporary narrowing of the arteries in response to cold temperatures or stress, leading to discoloration (often pale, but can be red during the rebound phase).
Chronic Regional Pain Syndrome (CRPS): A condition characterized by persistent burning pain and certain abnormalities that occur after injuries to bone and soft tissue. It can cause changes in skin temperature and color, which might be mistaken for signs of arterial blockage.