Which screening exam does not require an order in any setting?

Mammograms are a specific type of screening exam that can often be performed without a physician's order, allowing women of appropriate age to access this preventive service directly. This is particularly true in the context of recognized screening programs and guidelines that encourage breast cancer screening, making it more accessible for individuals.

In contrast, the other options typically have more stringent requirements for authorization. Colonoscopies usually require a referral or order from a healthcare provider to ensure appropriate indication and patient safety. X-rays, which can be used for various diagnostic purposes, often need a physician's order to validate the medical necessity for imaging. Blood tests also generally require a healthcare provider's order as they are conducted in a clinical setting to diagnose or monitor health conditions. Therefore, mammograms stand out as the only screening exam in this context that doesn’t necessarily require a physician's order in many settings.