Final answer:
A chest x-ray should be prioritized as the diagnostic study for an older adult client admitted with fluid volume excess, as it helps assess for pulmonary edema and other related lung pathologies.
Step-by-step explanation:
When an older adult client is admitted with fluid volume excess, the nurse should prioritize a chest x-ray as the diagnostic study. This is because a chest x-ray is typically the initial test used to assess for signs of fluid overload, such as pulmonary edema, which is a common complication associated with fluid volume excess. Additionally, a chest x-ray can help to identify other potential causes or complications of the fluid volume excess, such as heart failure or lung pathologies.
Other tests such as echocardiography, thyroid function tests (T4 and TSH), and arterial blood gases (ABGs) can also be helpful in understanding the cause and extent of fluid volume excess within the body. An echocardiogram can evaluate heart function, but it would not be the initial test in this situation. Thyroid function tests would be pertinent if a thyroid dysfunction is suspected as a cause of the volume excess. ABGs would help understand the oxygen and carbon dioxide levels and the acid-base status but are less critical initially compared to the chest x-ray.