Which symptom would warrant immediate follow-up for a client presenting with fatigue and pallor?

The symptom that warrants immediate follow-up in a client presenting with fatigue and pallor is difficulty concentrating. This is indicative of potential underlying issues, such as anemia or other hematologic conditions, that could compromise oxygen delivery to the brain. Fatigue and pallor often point to a decrease in red blood cells or hemoglobin, leading to hypoxia, which can affect cognitive function. Therefore, difficulty concentrating could suggest that the client's condition is more severe and requires urgent evaluation and intervention to prevent further complications.

In contrast, previous surgeries, dietary habits, and family medical history, while relevant to the overall health assessment, do not immediately indicate a critical need for follow-up related to the acute symptoms of fatigue and pallor. These factors may influence the client's health and risks, but they do not directly signal an urgent medical issue in the context of the presenting symptoms.