**Question:** Mallika, a 21-year-old married female, presents to the ER with abdominal pain and slight vaginal bleeding. She tested positive for pregnancy two days ago. To rule out an ectopic pregnancy, the test that **CANNOT** be used is:

A. HCG test
B. Ultrasound
C. Blood pressure measurement
D. Complete blood count (CBC)

**Correct Answer:** C. Blood pressure measurement

**Core Concept:** The question is testing our understanding of the diagnostic tests available for ruling out an ectopic pregnancy and the appropriate use of these tests. An ectopic pregnancy is a pregnancy occurring outside the uterus, most commonly in the fallopian tube. The key tests to rule out an ectopic pregnancy include:

**Why the Correct Answer is Right:** Blood pressure measurement is a vital sign that assesses the overall cardiovascular status of a patient but does not provide any information regarding the pregnancy status or location of the pregnancy. Blood pressure is a non-specific indicator of overall health and does not help in ruling out an ectopic pregnancy.

**Why Each Wrong Option is Incorrect:**

A. HCG test (Maternal serum alpha-fetoprotein test): This test measures the level of human chorionic gonadotropin (HCG) in the blood. A rising HCG level indicates a viable intrauterine pregnancy, while a falling or stable level suggests an ectopic pregnancy. Using an HCG test is appropriate for ruling out an ectopic pregnancy as it directly assesses the pregnancy status.

B. Ultrasound: Transvaginal ultrasound is a valuable diagnostic tool for evaluating suspected ectopic pregnancies. It can visualize the gestational sac, fetal heartbeat, and can differentiate an intrauterine pregnancy from an ectopic pregnancy. Using ultrasound is relevant in ruling out an ectopic pregnancy.

D. Complete blood count (CBC): CBC assesses the overall health of a patient and is not specific to ruling out an ectopic pregnancy. While a CBC might show signs of hemoperitoneum (bleeding into the peritoneal cavity) in an ectopic pregnancy, it is not specific enough to rule out the condition as it does not differentiate between intrauterine and ectopic pregnancy.

**Clinical Pearl:** Ultrasound is commonly used in clinical practice to diagnose and rule out ectopic pregnancy. A transvaginal ultrasound can differentiate an intrauterine pregnancy from an ectopic pregnancy by examining the gestational sac, fetal heartbeat, and visualizing the location of the pregnancy (e.g., intrauterine or ectopic). This helps in diagnosing and ruling out ectopic pregnancy.