Can I compare blood results from different laboratories?
Not by comparing the numbers alone. Laboratories may use different methods, units and reference ranges. A result that looks higher on a new report may not represent a genuine deterioration. Bring both complete reports to the clinician, including dates, units and the ranges printed beside each result. [1]
Start with the actual test name
A broad label such as cholesterol or thyroid test can hide several different measurements. Check that the two reports are measuring the same thing before asking whether it has changed. A full report is more helpful than a screenshot of one flagged number because it preserves the test name, laboratory information and related results.
Units and reference ranges come next
A reference range belongs to the method and patient group used by that laboratory. MedlinePlus advises using the range on your own report, rather than a range found elsewhere. It also notes that laboratories use different methods and units. A red flag is a prompt to interpret a result, not a diagnosis. Equally, an unflagged result is not a guarantee that symptoms can be ignored. [1]
For trends, consistency helps
Where practical, using the same laboratory makes repeat results easier to follow. MedlinePlus specifically recommends trying to use the same laboratory when looking for trends. That does not mean an older report from elsewhere is useless. It means a clinician should check comparability before drawing a line between two numbers and calling it improvement or decline. [1]
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Record what was different that day
Preparation, food and drink, medicines, supplements and exercise may affect some results. Make a note of the collection time, any fasting instructions and what you actually did. Do not stop medicines to create a more comparable result without medical advice. If you were unwell at one collection but not the other, tell the clinician that too. [1]
What to bring to a private review
Bring both original reports, the reason each panel was requested, your symptoms, a medicine and supplement list, and any advice you were given. Ask: Are these genuinely comparable measurements? Is the difference clinically meaningful? Do I need repeat testing, a different test, or no further test? A clear answer can prevent an unnecessary repeat panel.
When a new result should not wait
If the laboratory or clinician has told you a result needs urgent action, follow that advice rather than waiting to organise a perfect comparison. New severe symptoms need assessment in their own right. An old reassuring result does not override how you feel now.
A useful next step
Ask The Online GP by The Wellness about a review of your existing reports before arranging another blood panel. Send the complete reports through the agreed route and ask what a consultation includes, whether further testing may be needed and what it would cost. The aim is a decision you understand, rather than another isolated set of numbers.
Common questions
Should I convert the units myself? Leave clinical comparisons to the reviewing clinician; arithmetic alone may not account for method differences. Is one laboratory necessarily wrong? No. Differences can arise from methods and reference ranges. Should I repeat every abnormal result? Not automatically. The clinical question, degree of abnormality and your history determine the next step.
Enquiry links
The Online GP consultation options
Ask The Wellness team on WhatsApp or email the team.
Sources
General information, not individual medical advice. Evidence checked as of October 2026.