Interlab Quality Control Quiz

Interlab Quality Control (External QC)

• Proficiency testing programs periodically provide clinical laboratories with samples of unknown concentrations.
• Essential for maintaining the accuracy of analytical methods over time.
• Helps to assess state-of-the-art performance across participating laboratories.
• The College of American Pathologists (CAP) proficiency program is regarded as the gold standard.

Samples for External Quality Control/Proficiency Testing

• Preferred proficiency test (PT) samples should be commutable with patient samples.
• Clinical samples, like serum, are pooled to prepare commutable samples, minimizing additives to maintain original state.
• Commutable PT samples are challenging and costlier to produce than noncommutable samples.

Conduct of External Quality Control Testing

• Unknown samples are sent from a reference laboratory to participating laboratories.
• Samples must be tested by personnel who analyze patient specimens with the same reagents and equipment.
• Testing results must be submitted promptly without sharing amongst participating laboratories during the testing cycle.
• Comparison studies can occur after testing for performance assessment and areas for improvement.

Interpretation of Proficiency Testing Results

• Performance criteria exist for analytes (e.g., ±2 SD from peer mean).
• Deviations greater than 2 SD indicate potential discrepancies in a laboratory’s results.
• Failure to identify discrepancies could result in facility closure recommendations.

Rationale for External Quality Control/Proficiency Testing

• Proficiency testing ensures the accuracy of patient results, providing clinicians with confidence.
• Serves as a continuous improvement tool and a troubleshooting guide for analytical errors.

Quality Control Materials/Control Samples

• QC materials act as surrogates for clinical samples tested daily like patient specimens.
• Available commercially in both liquid and lyophilized forms.
• Can be sourced from equipment/reagent manufacturers or third-party vendors.

Characteristics of an Ideal QC Material

• Resembles human samples with known analyte concentrations.
• Inexpensive, stable for extended periods, and free from communicable diseases.
• Must have convenient packaging for easy dispensing and storage.

Notes to Remember on QC Materials

• QC materials should closely resemble human samples and remain available for at least one year (same lot number).
• Different lot numbers have varied concentrations necessitating new mean and standard deviation estimates.
• Human control materials are preferable; however, bovine materials are common due to availability and safety concerns.
• QC materials must share the same matrix as the specimens being tested (e.g., serum samples for glucose measurements).
• Proper reconstitution of lyophilized materials is crucial to avoid incorrect control values.
• Deterioration of QC materials can occur post-opening due to mishandling; re-evaluate with fresh containers if issues arise.
• Assayed controls, while pricier, offer external accuracy checks and are standard in internal QC practices.