ROSH Gastrointestinal Practice Exam

What is a common laboratory finding in patients with gastric outlet obstruction?

1. Hypokalemia

2. Hyponatremia

3. Hypercalcemia

4. Hypernatremia

The correct answer is: Hypokalemia

In the context of gastric outlet obstruction, hypokalemia is a common laboratory finding due to the loss of potassium that can occur through persistent vomiting. When gastric contents are expelled repeatedly, as often happens in patients with gastric outlet obstruction, there is a significant loss of electrolytes, including potassium. This can lead to a decrease in serum potassium levels, resulting in hypokalemia, which is characterized by a potassium level of less than 3.5 mmol/L. Additionally, vomited gastric fluid typically contains a high concentration of hydrochloric acid, which can also lead to metabolic alkalosis and exacerbate the loss of potassium. The physiological stress and potential inadequate intake during this obstructive process further contribute to disturbances in electrolyte balance. The other listed options, which may seem plausible, do not typically correspond as directly to the pathophysiology seen in gastric outlet obstruction. For instance, hyponatremia could be seen in various conditions but is not a primary or common finding in this specific scenario, while hypercalcemia and hypernatremia would not be expected as direct results of the obstruction and associated vomiting. Thus, hypokalemia stands out as the most relevant and prevalent laboratory finding in this condition.