Final answer:
The priority diagnostic intervention is a FAST exam.
Step-by-step explanation:
The priority diagnostic intervention for a seriously injured patient with a weak, thready pulse, cool, clammy skin, instability of the pelvis, and blood at the urinary meatus is a diagnostic imaging test called a FAST exam (Focused Assessment with Sonography for Trauma).
A FAST exam is a bedside ultrasound examination that can help identify internal bleeding in the abdomen or pelvis. It is a quick and non-invasive procedure that can be performed by a trained healthcare professional at the patient's side.
By performing a FAST exam, healthcare providers can quickly assess the extent of the patient's injuries and determine the best course of treatment.