Feb 17, 2023

Defining and reporting on critical values in genetics (update Feb 2023)

Originally published February 8, 2022. Updated and republished February 17, 2023.

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Download this guide as a printable PDF.

As part of an initiative to harmonize critical value reporting across genetic laboratories in the Greater Toronto Area (GTA), we sent a survey of 11 questions via email to genetic laboratory directors in Ontario in July 2019 and also September to October 2019 since there was a paucity of data for critical values in genetics.

Based on the data, the Council formulated proposed guidelines that were circulated to individuals from Ontario genetic laboratory centres and respondents of the survey in November 2021, who supplied feedback.

We recommend all genetic laboratories consider implementing these guidelines into their critical value reporting.

Please supply any feedback on the guidelines or their implementation to Dr. Elaine Goh.

Update to guidelines 2023

One year after this guideline was published, we emailed the participating laboratories to gather further feedback.

The Ontario laboratories indicated:

  • they were following the guideline
  • the guideline allows for standardization of practices across the Ontario genetics laboratories
  • slight rewording of the critical results was needed which has been updated below and in the attached PDF download.

Critical patient type

  • Prenatal
  • Newborn
  • Oncology or
  • Expedited by the ordering physician

Critical results

  • Cytogenetics: Abnormal prenatal aneuploidy, microarray and susceptibility loci
  • Molecular: Unexpected results, and pathogenic variants in prenatal setting 

Reporting process

  • Insufficient or incorrectly labelled samples: Do not limit to reporting via mail
  • Critical results: Suggest in addition to routine process to either also call, email and/or fax the ordering provider.

Other resources on this topic

Authors / contact

Compiled by

Dr. Elaine Goh
Assistant Professor, Department of Laboratory Medicine and Pathobiology, University of Toronto
Division Head of Clinical Genetics, Trillium Health Partners



Dr. James Stavropoulos
Assistant Professor, Department of Laboratory Medicine and Pathobiology, University of Toronto and Clinical Lab Director of Genetics at The Hospital for Sick Children

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