75 g oral glucose tolerance test (OGTT)

Pick Ordered or Not ordered to see the note.

Indicated when

• —At diagnosis of PCOS, in all adults and adolescents, to assess glycemic status, where the international PCOS guideline recommends a 75 g OGTT as the preferred test regardless of BMI, with fasting glucose and/or A1C as fallback options of reduced accuracy if OGTT is not feasible [1, 2]
• —Reassessment of glycemic status in a patient with PCOS, every 1 to 3 years based on individual risk factors, or when planning pregnancy or seeking fertility treatment [1]
• —Risk factors for type 2 diabetes (overweight or obesity, hypertension, dyslipidemia, family history, prior gestational diabetes, or higher-risk population membership), where Diabetes Canada accepts fasting glucose and/or A1C, with OGTT as an option, for screening at guideline-directed intervals [3]
• —Gestational diabetes screening and diagnosis in pregnancy, where a 75 g OGTT is used either as a confirmatory step after an abnormal glucose challenge test, or as the sole one-step diagnostic test, depending on the approach used [6]

Not indicated when

• —As a routine addition to wellness bloodwork in a person with no diabetes risk factors and no PCOS diagnosis pending, in place of the simpler fasting glucose or A1C tests that guidelines actually call for first [3]

Why not

The OGTT is a longer, more burdensome test than a single fasting glucose or A1C: it requires 2 hours of serial blood draws after a glucose load, can cause transient nausea, and is not the guideline's first-line general-population screening test outside PCOS, so using it as a routine substitute adds burden without a clear benefit over the simpler test [3].

Better first step

Assess diabetes risk factors or confirm a PCOS diagnosis is being worked up first, then order the full 75 g OGTT where a guideline specifically calls for it (PCOS glycemic assessment, gestational diabetes screening, or confirming an abnormal simpler test), rather than as routine wellness testing [3, 1].

Typical ND rationale

An ND may recommend a 75 g OGTT over a single fasting glucose or A1C, reasoning that measuring the body's response to a glucose load over time gives a fuller picture of insulin resistance than a single fasting number.

Ontario coverage & CONO orderability

OHIP status

insured

Glucose tolerance test (L104), or L103 in pregnancy, is listed by name in the 2026 Schedule of Benefits for Laboratory Services, insured when a physician who has clinically assessed the patient orders it; up to 5 blood glucose determinations (plus 1 urine glucose) are allowed per sample under Essential Specifications, paragraph 9. The same test ordered by an ND is patient-paid regardless (Reg. 552 s.22).

CONO orderable

Yes — CONO list #73

CONO list item 73, blood: 'Glucose Tolerance Test.'

Linked conditions

• pcos ↗
• Insulin resistance ↗

Counselling script

“If you have risk factors for diabetes, are being worked up for PCOS, or are screening for diabetes in pregnancy, the 75 gram oral glucose tolerance test is the guideline-preferred way to check how your body handles sugar, and I'll order it today. Without one of those reasons, we don't need the full 2-hour test; a simpler fasting glucose or A1C covers routine screening, so I won't add the OGTT just to be thorough. If your situation changes, such as a new PCOS diagnosis or pregnancy, we'll revisit it then.”

Revisit if

• —New PCOS diagnosis being worked up
• —Pregnancy planned or confirmed
• —New risk factors for type 2 diabetes develop
• —Due for the next guideline-recommended reassessment interval

References

1. [1]International PCOS Network (2023). Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. linkGlycaemic status should be assessed at PCOS diagnosis in all adults and adolescents, and reassessed every 1 to 3 years based on risk
2. [2]International PCOS Network (2023). Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. linkA 75 g OGTT is recommended as the preferred, most accurate test to assess glycemic status in PCOS, regardless of BMI
3. [3]Diabetes Canada (2018). Diabetes Canada Clinical Practice Guidelines: Screening for Diabetes in Adults. linkScreen for type 2 diabetes using fasting plasma glucose and/or A1C, with OGTT as an option, in adults with risk factors at guideline-directed intervals
4. [4]Diabetes Canada (2018). Diabetes Canada Clinical Practice Guidelines: Definition, Classification and Diagnosis of Diabetes, Prediabetes and Metabolic Syndrome. linkImpaired glucose tolerance is a recognized prediabetes category, diagnosed via the OGTT
5. [5]Canadian Task Force on Preventive Health Care (2012). Recommendations on screening for type 2 diabetes in adults. linkolder guidelineNo routine screening at low risk; risk-calculator-based A1C screening every 3-5 years at high risk
6. [6]Diabetes Canada (2018). Diabetes Canada Clinical Practice Guidelines: Diabetes and Pregnancy (Chapter 36). linkThe preferred gestational diabetes screening approach uses a 75 g OGTT, either after an abnormal glucose challenge test or as a one-step diagnostic test
7. [7]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkGlucose tolerance test (L104) is listed by name in the 2026 OHIP Schedule
8. [8]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkCommunity lab tests are insured only when ordered under the Schedule by an authorized prescriber
9. [9]Government of Ontario (e-Laws) (2026). Health Insurance Act, R.R.O. 1990, Reg. 552: General, s. 22 (insured laboratory services). linkA lab test is insured only when ordered by a physician, midwife, or NP who has clinically assessed the patient
10. [10]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkTests ordered by anyone other than an authorized provider, including NDs, are not insured services