Differential Diagnosis for Purple Urine

Single most likely diagnosis

• Porphyria: This is a group of disorders that can lead to the accumulation of porphyrins in the body, which can cause urine to turn purple or reddish-purple upon exposure to sunlight. Certain types of porphyria, like porphyria cutanea tarda, are more commonly associated with this symptom.

Other Likely diagnoses

• Phenolphthalein ingestion: Phenolphthalein is a chemical that was once used in laxatives. When excreted in the urine, it can cause the urine to turn purple or reddish-purple due to its pH-sensitive properties.
• Beetroot or blackberry consumption: While not an infection, consuming beetroot or blackberries can temporarily turn urine pink or red, which might be mistaken for purple. However, this is not an infection and would not fit the question's criteria unless considering a very broad interpretation.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

• Rhabdomyolysis: Although rhabdomyolysis (a serious syndrome due to direct or indirect muscle injury) typically causes brown or tea-colored urine due to myoglobinuria, in rare cases, the urine might appear differently, including potentially purple, depending on the presence of other substances. It's crucial to consider this condition due to its severity and the need for prompt treatment.
• Septicemia or severe urinary tract infection with specific bacteria: Certain bacteria can produce pigments that might alter urine color. While rare, a severe infection could potentially lead to a change in urine color, including purple, especially if associated with specific bacterial metabolites.

Rare diagnoses

• Alkaptonuria: This is a rare genetic disorder that affects the breakdown of certain amino acids, leading to the accumulation of homogentisic acid. Urine from individuals with alkaptonuria can turn dark or black upon standing due to the oxidation of homogentisic acid, but it might be perceived as purple under certain conditions.
• Melanogenuria: In cases of melanoma, especially metastatic melanoma, melanin can be excreted in the urine, potentially causing it to darken or change color. While extremely rare, this could be considered in the differential diagnosis of purple urine, especially in patients with known melanoma.