**Core Concept**
The patient's presentation suggests a diagnosis of pelvic inflammatory disease (PID), which is a common complication of sexually transmitted infections (STIs). The combination of lower abdominal pain, fever, tender adnexal mass, and irregular periods, along with a new sexual partner and vaginal discharge, is highly suggestive of PID. The pathophysiology involves bacterial invasion of the upper genital tract, leading to inflammation and infection of the fallopian tubes, ovaries, and surrounding tissues.

**Why the Correct Answer is Right**
The most likely test result to be seen in this scenario is an elevated white blood cell count (WBC) with a left shift, indicating an acute inflammatory response. This is due to the body's immune response to the bacterial infection, characterized by an increase in neutrophils and other white blood cells in the peripheral blood. The presence of a tender adnexal mass and lower abdominal pain further supports this diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** A negative pregnancy test is unlikely to be seen in this scenario, as the patient's irregular periods and new sexual partner raise the suspicion of pregnancy, which is a common cause of lower abdominal pain and pelvic tenderness.

**Option B:** A low hemoglobin level is not directly related to the patient's presentation of PID. While anemia can be a complication of PID, it is not a specific or sensitive test result for this diagnosis.

**Option C:** A normal urinalysis is unlikely to be seen in this scenario, as the patient's presentation of lower abdominal pain and fever with a tender adnexal mass suggests a urinary tract infection (UTI) or PID, which can cause hematuria, pyuria, or other abnormalities on urinalysis.

**Option D:** A normal beta-hCG level is not directly related to the patient's presentation of PID. While a beta-hCG level can be ordered to rule out pregnancy, it is not a specific or sensitive test for PID.

**Clinical Pearl / High-Yield Fact**
In cases of suspected PID, it is essential to consider the patient's sexual history, including the number of sexual partners and the use of condoms, as well as the presence of any symptoms suggestive of STIs, such as vaginal discharge or lesions on the cervix or vagina.

**Correct Answer:** . Elevated white blood cell count (WBC) with a left shift.