Dark urine during flu: what to know

When the body has less water available, urine becomes more concentrated and may look deep yellow or amber. Fever can increase fluid loss, while nausea, a blocked nose or fatigue can make drinking harder. Some medicines and supplements can also alter urine colour. Flu itself does not explain every dark shade: brown or tea-coloured urine, yellowing of the eyes, pale stools, or unusual itching can point to a liver or bile problem. Burning, frequency or cloudy urine may suggest a urinary infection. Dark urine is a symptom, not a diagnosis.

Take frequent small drinks and include an oral rehydration drink if vomiting or diarrhoea is making fluids difficult to replace. Rest, monitor whether you are passing urine, and note its colour as you recover. Follow medicine instructions and check whether a newly started product lists urine-colour changes. Do not force large amounts of water quickly. If you cannot keep fluids down, contact a clinician for advice.

Seek urgent help for very little or no urine, fainting, confusion, severe weakness, trouble breathing, or inability to keep fluids down. Arrange prompt medical review if urine stays brown or tea-coloured, blood is visible, you develop yellow skin or eyes, severe abdominal or back pain, or painful urination. A clinician may examine you and test urine and blood to distinguish concentration from infection, bleeding or liver-related causes.

Ask whether your symptoms fit dehydration, whether any flu medicine could affect the colour, and whether urine or blood tests are appropriate. Mention fever, vomiting, diarrhoea, new medicines, pain, changes in bowel motions and how often you are urinating.