Your results have arrived in the patient portal before your doctor has had a chance to call, and now you are staring at a column of numbers, a few of them flagged in bold. Most Ottawa patients have been there. This guide explains how to read a report from an Ontario community laboratory, what the flags and ranges actually mean, and how to tell the difference between a number worth a question and a number worth a phone call.
The anatomy of a lab report
Whatever the test, each line of a Bio-Test report contains the same five pieces of information:
- Test name, often abbreviated: Hgb for hemoglobin, ALT for alanine aminotransferase, TSH for thyroid stimulating hormone
- Your result: the value measured in your sample
- Units: the scale the result is reported on, which in Canada is usually the SI system, for example mmol/L for glucose and cholesterol, g/L for hemoglobin, and µmol/L for creatinine
- Reference range: the interval the laboratory considers typical for a healthy population, sometimes labelled reference interval
- Flag: a marker such as H (high) or L (low) when the result falls outside the reference range
Because Canadian units differ from the mg/dL units used in the United States, a glucose of 5.5 mmol/L and a glucose of 99 mg/dL are the same number expressed two ways. Be careful when comparing your report with figures from American websites.
What a reference range is, and is not
A reference range is built by testing a large group of healthy people and taking the middle 95 per cent of their results. That construction has an important consequence: about one healthy person in twenty will fall outside the range on any given test simply by chance, and if your panel has twenty tests on it, the odds of at least one flag are high even when nothing is wrong. Ranges also differ between laboratories because methods and analysers differ, which is why you should always compare your result with the range printed beside it, not with a range from another lab or from the internet.
Some ranges depend on who you are. Hemoglobin and ferritin have separate ranges for men and women; eGFR is interpreted differently with age; hormone ranges shift with time of day and menstrual cycle. A flag tells you a value is outside the interval; it does not tell you whether that matters for you.
Reading the flags sensibly
An H or L is a prompt to your provider, not a verdict. Three questions help put a flag in perspective, and they are the same questions your physician will ask:
- How far outside the range is it? A hemoglobin one gram below the lower limit and one that is thirty grams below are very different situations.
- Is it new? A value that has been slightly high on every report for five years usually means less than one that has changed suddenly. This is where trends matter.
- Do other results agree? A single high liver enzyme with everything else normal reads differently from several abnormal liver tests together.
Critical results, values far enough outside the range that they need prompt attention, are handled differently: laboratories phone the ordering provider directly as soon as they are confirmed. If something on your report were urgent, your provider would already know.
Why the same test can vary from visit to visit
Small differences between results are normal and expected. Your own biology varies from day to day and hour to hour; hydration, a meal, exercise, sleep, illness and medications all move results. Whether you fasted, and for how long, changes glucose and triglycerides in particular; our preparation guide explains which tests are affected. On top of that, every measurement has a small analytical variation. For most routine tests, a change has to be larger than these combined effects before it is considered meaningful, and your physician has a sense of that threshold for each test.
A quick map of common tests
Each of these has a full explainer on our blog if you want to go deeper:
- Complete blood count (CBC): red cells, white cells and platelets; hemoglobin is the line most people look at first
- Electrolytes, creatinine and eGFR: kidney function and fluid balance, usually reported together as a metabolic panel
- ALT, AST and other liver tests
- TSH for the thyroid; a high TSH generally points to an underactive gland, the opposite of what many people assume
- HbA1c for average blood sugar over about three months
- Cholesterol and lipids, where the target depends on your overall cardiovascular risk rather than a single cut-off
How results reach you in Ontario
Results are reported to the practitioner who ordered the test, and copies go to any other provider listed on the requisition. Ontario providers can also see results from hospitals and community labs in the province's Ontario Laboratories Information System. As a Bio-Test patient you can view your own results through our patient portal, and the Bio-Test app shows them as soon as they are released, with the lab's own reference range, a plain-language note on what each test measures, and a trend across your visits. Note that community-lab results do not automatically appear in hospital patient portals such as MyChart; our article on how long results take explains why and what turnaround to expect.
What to do with a flagged result
Do not change a medication or start a supplement on the strength of a report alone. Write down your questions, note anything unusual about the day of the test, such as a missed fast or a recent illness, and raise them at your follow-up. If you have a result that worries you and you have not heard from your clinic within the time they suggested, call them; that is a reasonable thing to do. Lab staff can confirm that a result has been released but cannot interpret it, because the meaning depends on your history, which only your provider has.
Reading your Bio-Test report with confidence
A lab report is a set of measurements, not a diagnosis, and the flags are there to start a conversation with your physician rather than to end one. When your next requisition comes, our preparation guide will help you avoid the fasting and timing pitfalls that produce misleading numbers, and any of our 11 patient service centres can collect it on a walk-in basis, or you can book online. Ask at the desk if you have a question about how reports are delivered.