EQA Programs – Grading Schemes

Clinical Bacteriology

Grading scheme is on a 4-point scale, and addresses identification, urine colony count, antimicrobial susceptibility testing, Gram stain analysis and interpretation, and importantly, clinical relevancy reporting of the challenge.

As more emphasis is placed on Clinical Relevancy Reporting, a grade of 4 is now achieved through correct Antimicrobial Profile Reporting and descriptive reporting, e.g. specifying MRSA, ESBL producer, VRE, and Notification of Public Health, i.e., Salmonella from a stool sample.

Over the years, CMPT has reported to laboratories in a number of formats.

  • Between 1982 and 1986 CMPT used numeric grading based on a 3-2-1 evaluation. This grading scheme was too linear and did not fairly distinguish performance so it was replaced with an excellent-acceptable-unacceptable (E-A-U) format.
  • As samples evolved to a more clinically oriented scale, the E-A-U format became less workable. As an interim format, CMPT adopted a two-point scale (acceptable or unacceptable).
  • In May 1999, CMPT changed its grading process to the new numeric-grading format (0, 1, 3, 4) as shown in Grading Table (pdf).

Enteric Parasitology

Grading is based on a 2-point scale (acceptable or unacceptable). For grading purposes, when a sample consists of paired results (a concentrate and stained smear), grades are based on the results of the combined pair.

When only fixed smears are sent, each fixed smear is graded on its own. See assessment scale (pdf).

Water Microbiology

Challenges are graded against the Guidelines for Canadian Drinking Water Quality (4th edition) Health and Welfare Canada.

See Water Grading Schemes (pdf)

Measurement Uncertainty:

CMPT uses the following formula to calculate the Measurement Uncertainty for all internal QA/QC samples tested:

Fractional Uncertainty =   Standard Deviation or Uncertainty in count ÷ Mean

Percentage Uncertainty = [Standard Deviation ÷ Mean] x 100%

Measurement Uncertainty (MU) can be defined as the ratio of the standard deviation to the mean (coefficient of variation). It measures the variability or dispersion of observed values in a frequency distribution.

This standardized measure shows the allowable variability in relation to the group mean of the distribution and has been expressed in percentage next to the result. It provides similar information as estimates of Allowable Error or Total Allowable Error.

Clostridium difficile, Shiga Toxin, Trichomonas vaginalis, Screening Bacteriology

Results for these programs are reported as Positive / Negative, thus grading is based on a 2-point scale: Acceptable / Unacceptable.

Mycology

Acceptable: Report is technically correct and clinically appropriate. Slide or Culture or Susceptibility is correctly identified.

Acceptable**: Report contains deficiencies, but within the limits of acceptable. Culture may be identified correctly only to the class, or genus level. Nomenclature errors would not likely lead to errors in clinical judgement or decision making.

Unacceptable: Report contains errors that could result in incorrect interpretation and actions. Significant error.

Ungraded: Report cannot be fairly assessed.