## **Core Concept**
A normal CD4 cell count, also known as the CD4 T lymphocyte count, is a critical measure of the immune system's health, particularly in assessing the body's ability to fight off infections and diseases. CD4 cells, also known as T helper cells, play a vital role in the immune response by assisting in the activation and direction of other immune cells. The normal range for CD4 cell count in a healthy individual is typically between 500 to 1600 cells per microliter (μL) of blood.

## **Why the Correct Answer is Right**
The correct answer, , indicates a CD4 cell count of 500-1600 cells/μL, which is considered the normal range for a healthy adult. This range is crucial for the proper functioning of the immune system. A CD4 count within this range suggests that the individual's immune system is likely functioning correctly, and they are less likely to be susceptible to opportunistic infections.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a very low CD4 count, which would indicate severe immune suppression, often seen in advanced stages of HIV infection or AIDS. This is far below the normal range.
- **Option B:** This option indicates a low CD4 count, which might suggest some level of immune compromise but is still lower than the normal range.
- **Option D:** This option presents a very narrow and high range, which, although partially within normal limits, does not accurately represent the full normal range of CD4 cell counts.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that a normal CD4 count ranges from 500 to 1600 cells/μL. HIV infection is typically characterized by a decrease in CD4 count, and monitoring this count is crucial for assessing the progression of the disease and the effectiveness of antiretroviral therapy (ART). A CD4 count below 200 cells/μL is often used as a criterion for diagnosing AIDS in individuals with HIV infection.

## **Correct Answer:** . 500-1600 cells/μL