## **Core Concept**
Postcoital bleeding, also known as postcoital hemorrhage, refers to vaginal bleeding that occurs after sexual intercourse. In a 60-year-old lady, this symptom is considered abnormal and warrants investigation to rule out underlying malignancy or other serious conditions. The primary concern in this age group is to identify or exclude cervical, endometrial, or vaginal cancer.

## **Why the Correct Answer is Right**
The correct answer, **Endometrial biopsy**, is justified because postcoital bleeding in a postmenopausal woman is a red flag symptom for endometrial cancer. Endometrial biopsy is a straightforward and effective method to sample the endometrium for histological examination. It can help diagnose endometrial cancer, polyps, or other abnormalities that could cause bleeding. Given the patient's age and symptom, directly assessing the endometrium is crucial.

## **Why Each Wrong Option is Incorrect**
- **Option A: Ultrasound**: While ultrasound can be useful in evaluating the uterus and adnexa, it is not the most direct or specific investigation for postcoital bleeding in this context. It can help identify abnormalities but does not provide a tissue diagnosis.
- **Option B: Pap smear**: A Pap smear is a screening tool for cervical cancer but is not the immediate next step for investigating postcoital bleeding. It may not directly identify the cause of bleeding and is more suited for screening asymptomatic women.
- **Option C: Colposcopy**: Colposcopy is useful for evaluating the cervix, vagina, and vulva for abnormalities and is often used after an abnormal Pap smear. While it can help identify lesions, it is not the first-line investigation for postcoital bleeding in a postmenopausal woman.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that postcoital bleeding, especially in postmenopausal women, is considered a high-risk symptom for malignancy until proven otherwise. Therefore, prompt and thorough investigation, often starting with endometrial biopsy, is critical. Remember, the differential diagnoses include but are not limited to cervical, endometrial, or vaginal cancer, and benign conditions like cervical polyps or endometrial hyperplasia.

## **Correct Answer:** . Endometrial biopsy