## **Core Concept**
Orthostatic hypotension, also known as postural hypotension, is a form of low blood pressure that happens when standing up from sitting or lying down. It is a significant drop in blood pressure that can lead to dizziness, lightheadedness, or even fainting. The condition is diagnosed based on specific criteria related to the drop in blood pressure upon standing.

## **Why the Correct Answer is Right**
The correct answer is a drop of ≥20 mmHg in systolic blood pressure within 3 minutes of standing. This criterion is used because it reflects a significant change in blood pressure that can lead to symptoms. The body normally compensates for the effects of gravity when standing by increasing heart rate and vascular tone to maintain blood pressure. A drop of ≥20 mmHg indicates a failure of these compensatory mechanisms.

## **Why Each Wrong Option is Incorrect**
- **Option A:** A drop of <10 mmHg is not considered significant for diagnosing orthostatic hypotension. This change could be within normal physiological variation and not indicative of the condition. - **Option B:** A drop of ≥10 mmHg might be considered a mild change and is not the standard criterion for diagnosing orthostatic hypotension. - **Option D:** A drop of ≥30 mmHg is also indicative of orthostatic hypotension but specifying ≥20 mmHg is the widely accepted criterion. ## **Clinical Pearl / High-Yield Fact** A key point to remember is that orthostatic hypotension can be caused by various factors including dehydration, certain medications (like diuretics and beta-blockers), and autonomic dysfunction. Testing for orthostatic hypotension involves measuring blood pressure after the patient has been lying down for at least 5 minutes and then again after standing for at least 1-3 minutes. ## **Correct Answer:** . ≥20 mmHg.