Which describes a Double Blind Sample?

• A. An external QA sample disguised as a production sample, not identified as QA to lab.
• B. An external QA sample identified as QA to the lab, but parameter concentrations are unknown to personnel.
• C. A sample of known matrix without analyte.
• D. A sample of known matrix with added analyte.

Answer: (A)

A double blind sample is an external quality assessment sample that is presented to the laboratory as if it were a routine production sample, with no indication to the lab that it is a QA sample. This means the lab handles, tests, and reports it just like any real patient or production specimen, without bias or altered procedures that might come from knowing it’s being used for QA. The goal is to measure the lab’s performance in a real-world setting, and then compare the result to the known target values later to judge accuracy and reliability.

This is why the best description is an external QA sample disguised as a production sample and not identified as QA to the lab. If the lab knew it was QA, or the concentrations were undisclosed but the QA status was clear, it would not test the lab’s routine performance in an unbiased, real-world way.