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Proficiency Testing/External Quality Assessment Frequently Asked Questions

Below are answers to commonly asked questions pertaining to performance and interpretation of CAP PT/EQA programs. To make it easy to find answers, the questions are categorized by discipline.


The evaluation report lists your results, the statistics for your peer group, and your normalized results as a standard deviation index (SDI). This value is obtained by subtracting the peer group mean from your result and then dividing by the standard deviation.

The SDI is calculated from the unrounded (or more precise) figures. For small numbers, the differences attributed to rounding can be rather significant. Nevertheless, the “true” SDI is displayed on the evaluation report. The participant is not able to calculate SDI separately with the other rounded numbers provided on the evaluation report.

The CAP sometimes includes proficiency testing/external quality assessment (PT/EQA) specimens that assess the ability of laboratory staff to make difficult distinctions, to deal with special interferences or circumstances, or that may challenge the routine capabilities of many well-run laboratories. In these cases, the PT/EQA specimen is not graded by design. In some situations, an entire PT/EQA program may consist of educational, ungraded specimens designed to help subscribers improve their skills and capabilities. Educational PT/EQA challenges are designated with an evaluation code 26. These challenges are not formally graded, and laboratories should utilize data in the participant summery (PS) report to perform a self-evaluation. Common methods used are using alternative peer groups for quantitative data and surmising the correct response from other participants or PT/EQA providers intent for qualitative data.

This happens when we have an alert on the result form. In some instances, a particular manufacturer has 2 different reagent lots in use. The manufacturer completed the studies and determined that these reagents performed differently on PT material. The CAP collects the data and forms peer group by method/instrument/reagent not to penalize laboratories using different reagents. When the laboratory selects a reagent (original or new) on the result form, the data will be displayed on top of the dotted line and peer group will be formed by method/instrument/reagent. When a laboratory does not select a reagent because it doesn’t apply to them, their data will be displayed on the bottom of the dotted line and the peer group will be formed by method/instrument.

Sometimes, fewer than 80% of participants or referees (for Clinical Laboratory Improvement Amendments of 1988 [CLIA] regulated analytes) agree on what is the correct response for a challenge. In this case, the challenge is not graded. The CAP does not believe it is reasonable to hold laboratories accountable for interpreting challenges that did not meet the expected criteria.

The minimum and maximum values provided in the PS report are not the limits of acceptability. These are the lowest and highest values reported for that peer group. The acceptable limits are located on your evaluation report.

Clerical errors cannot be regraded. Document that your laboratory performed a self-evaluation and compared its results to the intended response when provided in the PS report. Clerical errors may indicate a need for additional staff training, review of instructions provided with the PT/EQA program, addition of a second reviewer, or investigation of the reporting format provided by the testing device.

At minimum, any concern about the performance of any assay in the laboratory should trigger an informal process improvement assessment. A single unacceptable response (due to a clerical error) may not lead to significant change in the laboratory, but the cause of an unacceptable response must be determined, to the extent possible, and triaged appropriately by laboratory leadership. Conversely, investigation of a single unacceptable response could identify a situation requiring a complex improvement plan requiring assay re-validation. Therefore, review and assessment of all unacceptable responses, regardless of whether the laboratory achieves an overall acceptable score for the program, is recommended. An unsuccessful event indicates the laboratory did not achieve overall acceptable concordance with the intended responses (eg, did not achieve a passing score). In this situation, a comprehensive process improvement assessment should be initiated with appropriate corrective action taken for each unacceptable result.


Accuracy-based specimens are collected by drawing donors and pooling the serum from multiple donors as described in the modified CLSI C37A Preparation and Validation of Commutable Frozen Human Serum Pools as Secondary Reference Materials for Cholesterol Measurement Procedures, Approved Guideline. There are no additives, preservatives, or spikes added to the specimens. These specimens should behave in the same manner as patient specimens.


Here are the CAP recommendations and requirements for PT/EQA.

If you need further assistance, contact the Customer Contact Center and provide as much information as possible to help triage your request (eg, is your laboratory doing next-generation sequencing for somatic or germline purposes? Is your laboratory doing a panel, genome or exome testing? What genes is your laboratory testing for?).

Usually there is an extra space or inappropriate punctuation added to the customer’s result that might be difficult to see on the evaluation reports. Review the PS report for clarification. Laboratories should conform to the most recent HGVS recommendations. The following are inappropriate responses and are considered unacceptable:

  • The use of “X” to indicate a translation stop codon
  • Extra spaces (eg, c.145 G>A or p. Arg541*)
  • Incorrect usage/mixing of upper and/or lowercase letters (eg, p.GLN541*, c.123c>t, C.Pro543Arg,p.Gln451ter)
  • Reporting of the amino acid change inside parentheses (p.Gln541*). Per HGVS, the parentheses should be after the p., ie, p.(Gln541*)
  • Incorrect short form for frame shifts (eg, p.Arg123Profs, p.Arg123fs*3). The short form should indicate the first amino acid changed, its position and “fs” without further detail (eg, p.Arg123fs)
  • Missing punctuation (eg, c145G>A)


The CAP PT/EQA is designed to assess how well laboratories perform direct analyte measurements. Most calculated analytes values except for hemoglobin (estimated), because it is a regulated analyte, should not be reported. The following are examples of analytes derived from a calculation that should not be reported: LDL cholesterol, total iron-binding capacity (TIBC), osmolality, and free testosterone.

The CAP PT/EQA is designed to assess how well laboratories perform direct analyte measurements. Oxygen saturation (calculated) is derived from a calculation using other directly measured blood gas analytes. The Blood Oximetry (SO) program includes reporting options for oxyhemoglobin but does not include a reporting option for oxygen saturation.

The 4th Universal Definition of Myocardial Infarction, along with the International Federation for Clinical Chemistry Committee on Clinical Applications of Cardiac Biomarkers (IFCC C-CB), recommend reporting high-sensitivity troponin concentrations in nanograms per liter (ng/L), as well as reporting results in whole numbers. Contemporary troponin results can be reported in micrograms per liter (μg/L) or nanograms per milliliter (ng/mL). In the current era of electronic medical records reporting, test results to multiple decimal places can lead to misinterpretation of results and contribute to medical error. Reporting high-sensitivity troponin results in whole numbers and with appropriate concentration units (ng/L) avoids ambiguity of reporting results containing numerous zeros after the decimal point.


No. The FL6 program is designed for laboratories who are performing flow cytometry analysis on patients being treated with immunotherapy regimens (CAR-T and others).

No. The FL8 program asks participants to identify if MRD is present in mature B-Cell disorders. It is not limited to one disease type.

No. The BALL program allows for laboratories who are using COG and/or LDT assays to report.

In order to provide robust challenges to our customers, we use a cell line/whole blood mixture for the FL3 program. It may be beneficial to run unstained cells to assist in determining the antibody distribution of the population of interest.

For wet challenges, your laboratory only needs to report the antigens that it would for a patient. If you do not test an antigen, leave that section blank on the result form.


In a continuing effort to monitor the accuracy and reporting of the International Normalized Ratio (INR), the CAP has implemented an additional grading scheme for the INR. In addition to the grading scheme that is based upon the comparison of your laboratory’s INR to that of your peer group, a second evaluation will be provided. This evaluation compares your laboratory’s reported INR to a calculated INR that is based upon the International Sensitivity Index (ISI), the mean normal PT used to calculate the INR, and the PT result reported for each challenge that you provided on the result form. If you report the INR, but did not report the ISI, the mean normal PT and the PT on the result form, the summary will indicate unacceptable performance. For regulatory and PT purposes, you must report the PT, even if your institution only requires the reporting of the INR on patients. Prothrombin time is a regulated analyte required under CLIA. The values that your laboratory reported might not have been sufficiently abnormal to cause a failing INR score in comparison with your peer group. However, a systematic error of the type detected and reported in this summary could be clinically significant, now and/or at the time of a change of reagents. As you know, it is extremely important for patient care to produce accurate INRs. Accordingly, the CAP strongly recommends that you examine the method used in your laboratory if your laboratory fails the special INR evaluation. For the special INR evaluation, there are several criteria required to determine the accuracy of the reported INRs. We must receive the PT INR results and reported INRs for at least four challenges in addition to the reported ISI and mean reference range PT. If fewer than four challenges are provided, we cannot assess the accuracy of the INRs and the result will be Insufficient Data for Evaluation. If at least 80% of the reported INRs are within ± 0.2 of the calculated INR, the result is Acceptable Performance.


Participants should reference the online Hematology Glossary before the Hematology Atlas as the glossary is updated yearly, whereas, the atlas is updated every 10 years. Participants should read the clinical histories which contain information to help them with their response(s). Identify the arrowed cell and not surrounding cells. No two image challenges will have the same master list identification.

Participants should read the clinical histories which contain information to help them with their platelet estimate response(s).

If you are enrolled in an automated hematology program that includes a manual differential (10 pictures), the manual differential takes precedence over the automated differential.


A committee of pathologists and histotechnologists from the CAP and NSH determine which stains and tissues will be assessed in each challenge. Specific tissues and stains are selected to identify common problems (eg, fixation and processing of fatty breast tissue; optimal cytologic detail in decalcified bone marrow biopsies; proper embedding and sectioning of skin biopsies; or optimum preparation of amyloid stains). The committee strives to include cases that will allow laboratories to identify areas that can be improved.

The CAP/NSH Histotechnology Committee is pleased to offer a resource for laboratory staff to use for educational purposes and troubleshooting fixation, microtomy, and H&E staining technical problems. Participants of the HistoQIP programs that feature H&E staining can click Access e-LAB Solutions Suite, select their laboratory, then click Evaluation Reports to view the specific comments associated with their individual program.

By clicking on any comment link within your laboratory’s evaluation report, the online Digital Reference Tool (DRT) for H&E Staining will open to a web page that describes that problem, its cause(s) potential solutions, and digital images illustrating the artifact. Clicking on the thumbnail image will open DigitalScope, a digital microscope viewer, to show a stained microscopic image of the artifact, staining problem or technical issue. Each image is navigable in the same manner as a glass slide under a microscope, can be easily focused to a higher or lower magnification, and has annotation for that comment. There are multiple digital image examples associated with each artifact.

Note: The DRT does not address problems, causes, or potential solutions for IHC staining at this time.

The DRT can be used:

  • As a learning exercise for laboratory staff to visualize exact problems reported in the HistoQIP evaluation report on the laboratory’s daily work, and then to use the troubleshooting guides to improve performance.
  • As a competency assessment tool for laboratory staff who must complete annual demonstration of their technical knowledge and skills.
  • As an educational enhancement for staff experiencing performance problems.
  • As a method for delivering continuing education in a concise, meaningful format that directly correlates with laboratory bench duties.
  • As a teaching tool for students and employees seeking to learn skills that can help them prepare for histotechnology certification.


You may send out your PT/EQA slides for staining and digital analysis to a reference laboratory if that is in your laboratory procedures and as long as the reference laboratory and their software is not quantitating or interpreting the results.


If your evaluation is nonlinear, but your results are similar to your peer group, the nonlinearity may be inherent in the method and is not specific to your instrument. The nonlinearity may also be due to a matrix effect in the calibration verification/linearity (CVL) material. It may be helpful to review the Peer Results Summary Table included in your evaluation report to further assess peer group performance.

The linearity evaluation is based solely on your laboratory's results. The calibration verification compares your results to a peer group mean. Several factors such reporting wrong unit of measure, incorrect specimen handling, and differing lots of reagents and calibrators can contribute to a different evaluation.


The United States federal government regulations require that culture challenges be a mixture of report all challenges and principle pathogen challenges. If the PT/EQA kit instructions or result form say to report all organisms, laboratories are to report everything that grows, even organisms their laboratory would not typically report because it might be considered normal flora. If the PT/EQA instructions indicate to report principle pathogen(s), laboratories should report the organism(s) that are causing the infection. There are two sets of reporting boxes available on the result form and a laboratory can report up to two organisms. If the PT/EQA challenge contains an organism that would be pathogenic for the source and another organism that would be normal flora, participants are expected to only report the pathogen. Do not report the normal flora organism.

Laboratories should report PT/EQA to the level they report patient results. Each organism is graded individually, and all correct responses are considered good.

Laboratories should report only the testing they perform on the specimen. For example, if the glutamate dehydrogenase (GDH) antigen is negative and you would not test for the toxin, you should report the toxin as, “test not performed.” GDH is regulated as bacterial antigen and can be sent to CMS. If it is on a laboratory’s Analyte Reporting Selection (ARS), then GDH “test not performed” must be selected for all specimens if no testing for that analyte is performed.

No interpretation (NI) should only be used if CLSI/EUCAST have NI as the interpretation. If your institution reports only the minimum inhibitory concentration (MIC) but an interpretation is available from the organizations, NI will be considered a penalty. Since only interpretations are graded, do not report only the antifungal agent and MIC value. If the antifungal agent is entered and an MIC is entered an interpretation must be entered or a penalty will occur.

The D program material is live organisms lyophilized on a swab therefore it should work for molecular or enzyme immunoassay (EIA) testing; however, the D program is intended for culture use. There are no specific testing instructions for these procedures. CMS does allow bacterial identification by molecular methods.

Each GDH antigen and toxin testing include a method reporting area. Laboratories must ensure they enter the correct method.

A laboratory cannot use more than one method for a specimen. This would be considered as duplicate testing. A laboratory can rotate challenges or mailings through methods. For example, challenge 1, 3, and 5 can be done on one method and challenges 2 and 4 on another method. Each challenge has a method reporting area.

The D1 (Throat Culture) program can be tested by molecular methods.

Specific manufacturer detailed instructions that are included in the kit instructions come directly from that manufacturer. If no instructions are included for your manufacturer, it is assumed to test as a patient specimen, or contact the manufacturer to see if they can give you any specific instructions.


Only report up to 120 critical values for inpatient and 120 critical values for outpatients, up to 240 total.

Quality Practice FAQ1

You must enter the site location on the first page of the result form each quarter. Please enter the site and save. Your results will be shown in the next quarter cumulative report.

The more time goals you enter on the supplemental questions, the more robust your report will be. Please enter these time goals. Refer to the POC example below.


Sperm viability assessment on PT/EQA specimens should be performed in the same manner in which patient specimens are assessed. For additional information, consult the most up to date semen analysis manual for additional information such as the WHO laboratory manual for the Examination and processing of human semen, 5th edition.

Instructions are provided online via the "View Video(s)/Image(s)" link, which provide calculations and examples based on the type of chamber video you are viewing.