What should you know about dark blue urine?

Urine that looks dark blue or blue-green can be caused by a dye, medicine, cleaning product in the toilet, or a colour change that is actually green, brown, or cloudy. Concentration from fluid loss can make any unusual shade look stronger. Because true blue urine is uncommon, a persistent unexplained change should be discussed with a clinician.

Check whether the colour appears in a clean, clear container rather than only in the toilet, where blue cleaning products can mislead you. Dehydration after sweating, vomiting, or diarrhoea usually makes urine darker and may come with thirst or reduced urination. Heat Exhaustion can follow heat exposure with heavy sweating, headache, dizziness, nausea, and weakness. Hepatitis A or Hepatitis B may cause dark urine with tiredness, nausea, pale stools, or yellow eyes. Dark Urine gives useful background on colour changes and associated symptoms.

Write down when the colour started and review new medicines, supplements, food dyes, and medical tests that used a dye. If fluid loss is likely and you are otherwise well, move away from heat and take regular small drinks. Do not stop prescribed medicine without advice. If the urine remains blue, becomes cloudy or foul-smelling, or the change has no clear explanation, arrange a clinical review; urine testing can help separate pigment from infection or blood.

Get urgent help for blue-looking urine with confusion, fainting, severe weakness, inability to drink, very little urine, high fever, severe pain, or yellow skin and eyes. Seek prompt advice if the colour persists, returns repeatedly, or occurs with burning, blood, swelling, or marked tiredness. Heat-related symptoms can worsen quickly, so leave the hot environment and seek help if recovery is not prompt.

Ask whether the sample is truly blue, whether a medicine or dye could explain it, if urine or blood tests are needed, and which associated symptoms should prompt urgent care.