Clinician reference tool — not medical advice. This is a clinical decision-aid intended for healthcare professionals: it gives deterministic suggestions to think with, not a diagnosis or a prescription. If you’re a patient, you’re welcome to look around — but please review anything here with your own doctor; it isn’t a substitute for personalized medical care.
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Fasting insulin

Metabolic · specimen: blood

Rarely indicated

Also called: fasting insulin level, HOMA-IR, insulin resistance test, insulin, fasting

Chart note

ND-recommended test reviewed: fasting insulin / HOMA-IR.
Indications reviewed: insulin resistance or diabetes risk screening.
Not ordered. Rationale discussed: not part of Diabetes Canada's screening or diagnostic pathway, which uses fasting glucose and A1c. Ref: Diabetes Canada CPG, Screening for Diabetes in Adults.
Patient informed test available privately via ND. Patient given info page: https://labs.ajaxharwoodclinic.com/fasting-insulin/patient
Revisit if: fasting glucose or A1c become abnormal, or new symptoms of diabetes develop.

Indicated when

  • Documented hypoglycemia (Whipple's triad) in a person without diabetes, once drug, illness, hormone-deficiency and tumour causes have been considered: insulin is drawn with glucose, C-peptide, proinsulin and beta-hydroxybutyrate during an episode or a supervised fast, usually under endocrinology [6]

Not indicated when

  • Screening for or diagnosing insulin resistance, prediabetes, or type 2 diabetes in primary care; Diabetes Canada's screening and diagnostic pathway is built on fasting plasma glucose and/or A1c, and does not include fasting insulin or a HOMA-IR calculation [1]
  • Routine addition to a 'wellness' or hormone panel to explain fatigue, weight gain, or difficulty losing weight, without a recognized indication for a fasting insulin level

Why not

Diabetes Canada's clinical practice guideline screens for and diagnoses type 2 diabetes using fasting plasma glucose and/or A1c, not fasting insulin or a HOMA-IR calculation [1]. Ordering a test that sits outside that validated pathway produces a number without an established cutoff for action, which can prompt more testing or worry without changing the standard, glucose-based workup and lifestyle counselling that would happen anyway.

Better first step

For a concern about diabetes risk, order fasting plasma glucose and/or A1c per Diabetes Canada's screening guidance, rather than fasting insulin [1].

Typical ND rationale

An ND may order fasting insulin, often with HOMA-IR calculated from it, reasoning that insulin resistance can develop years before fasting glucose or A1c become abnormal, so catching a high insulin level earlier could prompt earlier lifestyle intervention.

Where the ND is right

The underlying concern is real: insulin resistance can be present before glucose or A1c becomes abnormal, and lifestyle counselling for at-risk patients is worthwhile whatever any single test shows. But no validated use of fasting insulin or HOMA-IR to screen for or manage it in primary care was found. Diabetes Canada screens with fasting glucose or A1c [1]. Insulin has one real clinical use: working up documented low blood sugar in someone without diabetes. That is done during an episode alongside other tests, not as a random fasting draw [6].

Ontario coverage & CONO orderability

OHIP status
insured
Listed by name in the 2026 Schedule of Benefits for Laboratory Services (L325 Insulin, fee $6.14). Insured when ordered by a physician, midwife, or NP who has clinically assessed the patient; the same test ordered by a naturopathic doctor is not an insured service and is billed privately (Reg. 552 s.22(1); SOB-LS 2026 preamble).
CONO orderable
Yes — CONO list #79
CONO list item 79, blood: 'Insulin, Fasting and Non-fasting.'

Linked conditions

Counselling script

“Fasting insulin and the HOMA-IR calculation aren't part of how we screen for diabetes risk in Canada, because our guidelines are built around fasting glucose and A1c instead. If diabetes risk is what you're worried about, I'd rather check your fasting glucose and A1c today, since those are the tests that actually guide what we do next.”

Revisit if

  • Fasting glucose or A1c becomes abnormal
  • New symptoms of diabetes (polyuria, polydipsia, unexplained weight loss)

References

  1. [1]Diabetes Canada (2018). Diabetes Canada Clinical Practice Guidelines: Screening for Diabetes in Adults. linkDiabetes Canada's screening and diagnostic pathway for type 2 diabetes uses fasting plasma glucose and/or A1c, not fasting insulin or HOMA-IR
  2. [2]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026) - L325 Insulin. linkInsulin (L325) is listed by name in the 2026 OHIP Schedule of Benefits for Laboratory Services
  3. [3]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
  4. [4]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
  5. [5]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
  6. [6]Endocrine Society (2009). Evaluation and Management of Adult Hypoglycemic Disorders: An Endocrine Society Clinical Practice Guideline. linkolder guidelineInsulin, C-peptide and glucose measured together during documented hypoglycemia (Whipple's triad) in non-diabetic adults suspected of endogenous hyperinsulinism
Evidence notes

C-peptide (CONO 46, 'C-peptide immunoreactivity') is a related but distinct test with its own validated indications (distinguishing insulin-dependent from non-insulin-dependent diabetes, evaluating hypoglycemia or suspected insulinoma), which were not researched in this session. It is deliberately not added to this record's aliases, so the paste-box matcher does not treat a C-peptide requisition line as equivalent to fasting insulin/HOMA-IR; this record's no_validated_use verdict does not apply to C-peptide. Flagged as a possible standalone record for a future batch. The claim that HOMA-IR lacks a standardized, cross-laboratory reference range is laboratory-medicine common knowledge but was not directly sourced in this session; it is not asserted in why_not for that reason, only the sourced claim that Diabetes Canada's pathway doesn't use it. Reviewer: verdict changed from no_validated_use to rarely, and linked to Reactive hypoglycemia (sugar crashes after eating), because insulin does have a validated (specialist) use. The Reactive hypoglycemia (sugar crashes after eating) page must make clear that the validated workup for suspected hypoglycemic disorders (insulin, C-peptide, and glucose drawn together during a supervised fast or spontaneous episode) is a distinct, specialist-directed protocol, not the single outpatient fasting insulin draw this record covers.