Proficiency Testing (PT) in Clinical Laboratories: Requirements, Enrollment, and Corrective Action

Proficiency testing (PT) — also called external quality assessment (EQA) outside the United States — is one of the most important quality assurance activities in clinical laboratory practice. It is also one of the most frequently cited deficiency areas during CLIA and CAP inspections.

This guide covers everything laboratory directors, managers, and quality coordinators need to know about PT: what it is, who must enroll, how to choose a PT provider, what constitutes acceptable performance, and how to respond when results are unsatisfactory.

What Is Proficiency Testing?

Proficiency testing is a program in which an external organization sends unknown specimens to participating laboratories. Each laboratory tests the specimens using its routine methods and reports results back to the PT provider. The provider compares each laboratory's results to those of peer laboratories and to established target values, then issues a performance report.

PT serves two purposes:

External verification — confirms that your laboratory's methods produce accurate results compared to other laboratories

Regulatory compliance — demonstrates to CMS, CAP, and other accreditation bodies that your laboratory meets minimum performance standards

Who Must Enroll in PT?

Under CLIA regulations (42 CFR Part 493), all laboratories performing regulated analytes under a Certificate of Compliance or Certificate of Accreditation must enroll in an approved PT program. Regulated analytes include:

• Routine chemistry (glucose, BUN, creatinine, electrolytes, liver enzymes, lipids)
• Hematology (CBC, differential)
• Coagulation (PT/INR, aPTT)
• Immunology (ABO/Rh, antibody screen, compatibility testing)
• Microbiology (bacteriology, mycobacteriology, mycology, parasitology, virology)
• Urinalysis
• Endocrinology (TSH, free T4, cortisol, hCG)
• Toxicology (therapeutic drug monitoring, drugs of abuse)

Laboratories with a Certificate of Waiver are not required to enroll in PT, but it is strongly recommended as a quality assurance measure.

Approved PT Providers

CMS maintains a list of approved PT providers. The most widely used include:

• CAP Surveys — the most comprehensive PT program, used by over 22,000 laboratories worldwide
• AAFP (American Academy of Family Physicians) — focuses on physician office laboratory testing
• API (American Proficiency Institute) — offers PT for most regulated analytes
• COLA — PT program for COLA-accredited laboratories
• New York State Department of Health — required for laboratories licensed in New York State

PT Frequency and Sample Requirements

CLIA requires that PT specimens be tested at least three times per year for each regulated analyte. Most PT programs send five specimens per event, three events per year (15 specimens total per analyte per year).

Critical rule: PT specimens must be tested in the same manner as patient specimens. You may not:
• Send PT specimens to a reference laboratory
• Test PT specimens multiple times and average the results
• Discuss PT results with other laboratories before the reporting deadline
• Use any method not used for routine patient testing

Violation of these rules is considered PT referral — a serious CLIA violation that can result in sanctions.

Acceptable Performance Criteria

CLIA establishes acceptable performance criteria for each regulated analyte. Performance is evaluated as:

• Percent deviation from target value — for quantitative analytes (e.g., glucose must be within ±10% of the target value)
• Graded response — for qualitative analytes (e.g., blood type must match the target exactly)

An analyte is considered unsatisfactory if the laboratory's result falls outside the acceptable performance criteria. A PT event is considered unsuccessful if the laboratory fails 2 or more of 5 specimens for the same analyte.

Consequence of unsuccessful PT: Two consecutive unsuccessful events for the same analyte results in loss of CLIA certification for that analyte until the laboratory demonstrates corrective action and passes a subsequent PT event.

Writing a PT Corrective Action

When a PT result is unsatisfactory, CLIA requires a written corrective action within 30 days. The corrective action must be retained for 2 years.

A complete PT corrective action includes:

Identification of the unsatisfactory result — analyte, PT event, result reported, target value, acceptable range

Investigation — review of patient results, QC records, calibration records, and reagent lot information from the time of PT testing

Root cause — the specific reason the PT result was unsatisfactory

Corrective action taken — specific steps to eliminate the root cause

Verification — evidence that the corrective action was effective (e.g., subsequent PT results, repeat QC, patient result review)

Signature of Laboratory Director — required by CLIA

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LabComply's PT Management module tracks enrollment status, testing deadlines, result entry, and corrective action completion for every regulated analyte — so no PT event is ever missed and every unsatisfactory result triggers an automatic corrective action workflow.