## **Core Concept**
The Prostate-Specific Antigen (PSA) test is a widely used screening tool for prostate cancer. PSA is a protein produced by the prostate gland, and its levels can be elevated in various conditions, including prostate cancer, prostatitis, and benign prostatic hyperplasia (BPH). The normal level of PSA is generally considered to be below 4 ng/mL.

## **Why the Correct Answer is Right**
The correct answer, ** 10 ng/mL - This option is incorrect because a PSA level above 10 ng/mL is considered elevated and may indicate the presence of prostate cancer or other prostate problems.
* **Option B:** > 20 ng/mL - This option is incorrect because a PSA level above 20 ng/mL is significantly elevated and may indicate a more advanced stage of prostate cancer.
* **Option D:** > 100 ng/mL - This option is incorrect because a PSA level above 100 ng/mL is extremely high and may indicate a very aggressive form of prostate cancer.

## **Clinical Pearl / High-Yield Fact**
A crucial point to remember is that a PSA level of 4-10 ng/mL is considered a "gray zone." Patients with PSA levels in this range may require further evaluation, including a prostate biopsy, to determine the cause of the elevated PSA. Additionally, some men with prostate cancer may have PSA levels below 4 ng/mL, highlighting the importance of considering other factors, such as family history and ethnicity, when interpreting PSA results.

## **Correct Answer:** . < 4 ng/mL