1. of, relating to, or used in diagnosis; serving to identify or determine the nature of a disease or condition
Usage: formal or technical; less common than the adjective 'diagnostic'

Examples

• The doctor ordered diagnostical tests to determine the cause of the patient's symptoms.
• Diagnostical procedures helped identify the infection quickly.
• The laboratory uses diagnostical equipment to analyze blood samples.
• A diagnostical approach was essential to solving the medical mystery.