If a patient has pulmonary oedema but pneumonia is suspected then can an x-ray still give a reliable diagnosis? is there another standard diagnostic test that can be used in these circumstances?

Combination: The answer lies in a combination of clinical history, and examination supported by specific imaging and laboratory testing which requires experience and training. Rely on the doctor treating you.

Typically, yes: Pulmonary edema is a diffuse problem and has a different appearance than pneumonia. Pneumonia is usually more focal and therefore, can often be differentiated from edema.