Diagnostic (adjective)

1. Relating to diagnosis, especially medical diagnosis.
2. Serving or intended to diagnose a problem or disease.
3. Providing information to help determine the nature or cause of a problem or disease.

Origin:

Late 19th century: from french diagnostique, from greek diagignōskein 'distinguish between', from dia- 'thoroughly' + gignōskein 'know'. the noun is from late 19th century.

Examples:

1. The doctor ordered several diagnostic tests to determine the cause of her symptoms.
2. The diagnostic equipment was able to detect the problem with the engine.
3. The diagnostic report showed that the patient had a rare form of cancer.
4. The diagnostic tools were essential in identifying the source of the contamination.
5. The diagnostic procedure was successful in detecting the underlying condition.