Brown mucous membranes indicate which condition?

• A. Dehydration
• B. Hypoxia
• C. Anaemia
• D. Methemoglobinemia (blood cells carry less O2), possibly from paracetamol ingestion)

Answer: (D)

Brown mucous membranes point to methemoglobinemia, where the iron in hemoglobin is oxidized to a form that cannot carry oxygen effectively. Even if the blood’s oxygen level seems okay, tissues aren’t getting the oxygen they need, so mucous membranes take on a chocolate-brown color rather than pink. A common trigger, especially in cats, is paracetamol (acetaminophen) ingestion, which overwhelms the body’s ability to keep hemoglobin in its usable form.

This is different from dehydration, which makes membranes dry and tacky but not brown; from hypoxia, which tends to produce bluish or pale membranes depending on the cause; and from anaemia, which makes membranes pale due to fewer red blood cells. If you see brown mucous membranes, it’s an emergency and warrants veterinary review.