Ontario Preoperative Testing Grid: What to Order (and What to Skip)

The Ontario preoperative testing “grid” is a practical decision table used to match patient risk factors and procedure needs to appropriate pre-op tests, instead of ordering routine testing for everyone. Many Ontario hospitals use grid-based approaches aligned with Choosing Wisely Canada recommendations that discourage baseline labs, ECGs, and chest X-rays for asymptomatic patients undergoing low-risk, non-cardiac surgery.

Why the grid exists

Choosing Wisely Canada includes recommendations from anesthesia and surgery groups that advise against baseline laboratory studies, baseline ECGs, and baseline chest X-rays in asymptomatic patients having low-risk, non-cardiac surgery. The goal is to reduce low-value testing that rarely changes management in low-risk situations, while still ensuring higher-risk patients get the right investigations before surgery.

Common tests in Ontario grids

In Ontario implementations, the grid typically covers tests such as CBC, electrolytes/creatinine, glucose (and sometimes LFT-related items), coagulation tests (INR/aPTT), ECG, chest X-ray, and blood bank testing (Group & Screen) when indicated by surgery type or patient factors.

• CBC: Commonly indicated for major surgery or when there is anemia/bleeding risk, active bleeding, malignancy/cancer, or significant cardiovascular disease.
• Creatinine/electrolytes (and related labs): Often considered with hypertension, renal/adrenal/pituitary/major endocrine disease, diabetes, or certain medications (e.g., diuretics, ACE inhibitor/ARB, lithium, digoxin) and known electrolyte issues.
• INR/aPTT: Commonly tied to bleeding disorders, liver disease, malnutrition/high alcohol intake, or anticoagulant use (institutional criteria may vary).
• ECG: Often recommended by grid criteria for older age (e.g., 70+) and/or known vascular/cardiac disease or multiple risk factors (such as HTN, CKD, DM, OSA, high BMI).
• Chest X-ray: Typically reserved for symptoms or specific clinical concerns rather than routine screening in asymptomatic patients.
• Group & Screen: Frequently driven by procedure-specific blood ordering schedules (e.g., MSBOS) rather than ordered for all patients.

How to use the grid safely

Use the grid after reviewing the patient’s history and medication list, then select only the tests that match the patient’s comorbidities and the planned procedure category. Avoid repeat testing when recent results exist and there has been no meaningful change in health status, because several Ontario directives specifically advise against unnecessary repeats.

If there is uncertainty about whether a test is required, Ontario grid examples recommend contacting the perioperative/anesthesia team for guidance rather than defaulting to ordering “just in case.” This type of standardized approach is also used to reduce ordering variation and support consistent perioperative decision-making across teams.

Downloadable Ontario examples

For real-world Ontario templates that can be used for training or to model local policy, see the Lakeridge Health Adult Pre-Operative Testing Grid (Medical Directive PDF). For a Canada-wide implementation toolkit that includes an example testing grid and the underlying Choosing Wisely recommendations, see Choosing Wisely Canada “Drop the Pre-Op” Toolkit (PDF).

Medical note: This article is informational and does not replace local hospital policy, surgeon/anesthesiologist instructions, or individual clinical judgment.

Download PDF: Ontario preoperative testing grid