Final answer:
A nurse should prioritize checking hemoglobin and hematocrit for anemia and TSH levels for thyroid function when a client complains of fatigue, listlessness, and reduced activity tolerance.
Step-by-step explanation:
When a client is experiencing symptoms of being tired, listless, and unable to tolerate activity at usual levels, a nurse should first review the client's hemoglobin and hematocrit levels for anemia as well as thyroid function tests, including TSH (thyroid-stimulating hormone) level, while assessing these complaints. Both anemia and thyroid dysfunction can cause fatigue and reduced activity tolerance, and these conditions are common causes of such symptoms. For example, a TSH deficiency could lead to hypothyroidism, which can present with weight gain and fatigue, as even a slight deficiency in thyroid hormone can have significant effects on energy levels and metabolism. Moreover, other lab values that might be relevant depending on the context and additional symptoms could include blood glucose levels, electrolytes, kidney and liver function tests, and possibly a complete blood count (CBC) to check for infections or blood disorders.