It is usually by culture; but blood tests are used as well but are not as accurate.

No, diagnostic procedures are used to identify a disease or condition. Once a diagnosis is established, treatment procedures are then implemented by healthcare providers.

Noninvasive procedures and invasive procedures

Are there non-invasive procedures that are considered treatment instead of only diagnostic in nature

A diagnostic radiological procedure uses wave energy to examine the body or its functions. For instance, diagnostic radiological procedures can include a chest x-ray, looking at the structures of the lungs and chest, or an echocardiogram, looking at the motion of the heart.