Which symptom is considered a red flag for a patient with a history of vomiting?

Bilious vomiting is considered a red flag, especially for a patient with a history of vomiting. This type of vomiting indicates the presence of bile in the vomit, which can be a sign of a more serious underlying condition, such as intestinal obstruction or other gastrointestinal issues. The presence of bile suggests a disruption in normal digestive function, which requires immediate medical attention.

In contrast, a normal appetite, mild headache, and stable weight do not typically indicate an urgent or severe condition. A normal appetite can suggest that the patient may not be as affected by an illness, mild headaches can be common and not necessarily alarming, and stable weight may reflect that there hasn't been significant fluid loss or nutritional deficiency. Each of these factors is less concerning compared to the implications of bilious vomiting, which warrants thorough evaluation and potential intervention.