As a researcher, I’ve now twice seen dark (brown/black) urine from subjects. Both times were from subjects completing a long ultra-endurance bike ride in the middle of the summer heat. Luckily, these subjects were participating in our study & urinated into a urine cup like the one below, instead of into the portable toilets dispersed throughout the race course (which would make it hard to see dark-colored urine), and sowe were able to catch this medical emergency and send them to the hospital.
WHAT DOES DARK-COLORED URINE USUALLY INDICATE & WHY IS IT A MEDICAL EMERGENCY?
Dark-colored urine is usually indicative of a condition called rhabdomyolysis, which is reversible if caught early enough; but if left untreated can result in death.
Most cases of rhabdomyolysis result from people pushing themselves really hard through work or exercise, especially in the heat.
Dark-colored urine often accompanies rhabdomyolysis because of the muscle breakdown (muscle fiber death) that occurs. The contents inside of the muscle are released into the bloodstream, and the kidneys have to work even harder to filter the blood to concentrate the urine. Often though, creatine kinase and myoglobin (from within the muscles that are released into the bloodstream) can enter the urine, giving it a darker appearance.
Rhabdomyolysis should be treated immediately to prevent further kidney (and potentially liver) damage. So if you’ve been working (or exercising) hard, and especially if you’re in the heat, pay attention to your urine color. If it becomes a brown or black color, head to the ER right away!
To minimize the chances of getting rhabdomyolysis, drink plenty of fluids during your workday to stay hydrated and maintain optimal kidney function. Don’t take on more work than you can handle, and if you start getting muscle cramping or experience any of the other signs of heat injury and/or illnesses, be sure to take a break and cool down.