Question

Diagnostic tests can be used to identify illnesses and underlying causes of symptoms

Answer 1

That statement is true

By definition, Diagnostic tests are medical tests that performed to aid in diagnosis or detection of a deceases.
And that include identifying illness and the underlying cause of the symptops

Answer 2

Diagnostic tests can be used to identify illnesses and underlying causes of symptoms. This is indeed true because diagnostic tests have been in use as tools that help doctors or psychologists to determine what is wrong with a patient and with that the probable disease.