Final answer:
Fatigue is a sign of leukopenia, a condition characterized by a deficiency of leukocytes that leads to a compromised immune system.
Step-by-step explanation:
The condition you are asking about is leukopenia, which is characterized by a lower than normal number of leukocytes (white blood cells) in the blood. Leukopenia can make an individual more susceptible to infections, as leukocytes are crucial for the immune system's response to pathogens. Out of the options provided, the sign of leukopenia is often associated with fatigue. This is due to the body's weakened defense against infections, which can result in the individual feeling overly tired. Other related signs can include fever and infections, such as a sore throat, which could be due to a compromised immune system.