Calibration Verification Standards are used according to Pennsylvania accreditation. Which statement is true?

• A. Pa accredited labs analyze a calibration verification standard at the beginning and end of each analysis day; after every ten samples; verify calibration curve with a low and high level.
• B. They replace the calibration curve entirely if the curve is invalid.
• C. Only a single verification standard is required at the start of the day.
• D. They are used to adjust the recovery percent.

Answer: (D)

Calibration Verification Standards are used to check how accurately the method recovers a known amount of analyte and, when needed, to adjust the reported recovery percent to reflect true performance. In the Pennsylvania accreditation context, these standards provide a check against bias from the extraction and analysis process, so the recovery percentage you report aligns with what actually occurred in practice. If the CVS results show the measured recovery is consistently off from the expected value, adjusting the recovery percent helps ensure the reported data represent reality rather than a drift or matrix effect.

This fits best because it centers on correcting or confirming the accuracy of recovery calculations, which is a key purpose of calibration verification in many accreditation schemes. The other statements describe procedures—like replacing calibration curves, using only a single standard at the start, or requiring verification at specific intervals—that don’t align with how CVS is intended to validate and, if necessary, adjust recovery performance.