How to Read Your Blood Test Results

Reference ranges are statistical, not personal

Reference intervals are built from the middle 95% of a supposedly healthy population — meaning 5% of healthy people will fall outside them by definition. A single value just outside the range is almost never a diagnosis on its own.

Optimal ranges — where the risk of disease is lowest — are often narrower than reference ranges. That is why a clinician might act on a ferritin of 20 (technically 'normal') or a TSH of 4.2 (technically 'normal') in a symptomatic patient.

Reading flags, units, and critical values

Reports typically flag values with L (low), H (high), or a critical alert. Units matter — Canadian labs use SI units (mmol/L, µmol/L, pmol/L) rather than U.S. mg/dL. When comparing to online sources, always confirm the units before drawing conclusions.

Trends beat single values

Two decades of research on chronic disease risk (cholesterol, HbA1c, kidney function, PSA) point to the same conclusion: the trajectory over years is more predictive than any single number. Keep your prior results and give them to every new clinician.

When to recheck an abnormal result

Mild, unexpected abnormalities should generally be repeated once before further workup — especially electrolytes, liver enzymes, and platelets, which are easily perturbed by acute conditions, hydration, or sample handling.

Book a review with a clinician

Ready to book? Reserve a private blood collection appointment on our Book Blood Collection page, or request a private requisition through blood test prescription.