What must be checked first prior to taking a blood sample?

The question asks what must be checked first prior to taking a blood sample.

In medical procedures, especially when collecting samples, patient safety and accurate identification are paramount.

• Patient Identity: Verifying the patient's identity is the most critical first step to ensure that the correct procedure is performed on the correct individual and that the sample is correctly attributed. Misidentification can lead to serious medical errors.
• Time and Date: While important for documentation and tracking, the time and date of sample collection are secondary to confirming the patient's identity.

Therefore, the first and most crucial check is the patient's identity.

The final answer is $\text{Patient Identity}$