Why do results differ between labs?

Because labs do not all measure things in exactly the same way. Different labs use different machines, chemical reagents and calibration methods, and some report results in different units. Each lab also sets its own reference range based on its methods and the population it tests. So the same blood sample sent to two labs can come back with slightly different numbers, and one lab may flag a value as high while another prints it as normal. For most routine tests the differences are small, but for some tests, such as tumour markers and certain hormones, they can be large enough to look like a real change.

Other factors add to the variation: the time of day the sample was taken, whether you had eaten, how long the sample sat before processing, how it was stored in heat or cold, and whether it was collected from a vein or a line. During chemotherapy, your team relies on trends from one test to the next to decide whether it is safe to treat. Switching labs can create changes that are not real, or hide changes that are. The practical answer is simple: use one reliable lab throughout treatment where you can, and tell your team whenever you change. This page explains the reasons; it cannot interpret your own results.

Tumour markers vary most

Different test kits for markers can give quite different values, so marker trends should always come from the same lab.

Units must match

A result in one unit can look very different from the same result in another unit.

Accreditation helps

Labs with recognised quality accreditation follow strict checks that improve reliability.

It cannot tell you whether a difference between two of your reports is a real change or just lab variation. Your team judges that using your history, symptoms and knowledge of the labs involved.

It also cannot tell you which lab near you is best. Ask your treating team for their recommendations, and choose reliability over lowest price.

A surprising result may be repeated

If a result does not fit the picture, your team may ask for a repeat, sometimes at the treatment centre.

Potassium is easily affected

Delays or rough handling can falsely raise potassium. A high reading may be rechecked before action.

Home collection needs care

Samples collected at home should reach the lab quickly and be kept at the right temperature.

Different hospitals, different ranges

Reports from other hospitals may use their own ranges. Bring the full reports so your team can compare properly.

Avoid ordering extra tests at many labs

Testing the same thing at several labs to compare usually creates confusion rather than clarity.

Digital reports are useful

PDF or app reports are easy to share and store, and reduce transcription errors.

Ask for explanations

If two reports seem to disagree, ask your team to explain rather than guessing.

Keep a lab note in your folder

Write the lab name beside each result in your records, so changes of lab are easy to spot.

Costs versus consistency

Switching to a cheaper lab for one test can save money but make trends harder to read. Discuss with your team.

Hospital labs and outside labs

Treatment centres often have their own labs that the team knows well. If you use an outside lab between visits, occasional tests at the centre help your team compare the two and understand any small, consistent differences between them.

Point-of-care tests

Quick finger-prick tests for sugar or haemoglobin are useful but can differ from full lab tests. Your team knows which to rely on for decisions.

Write down your usual lab details

Keep the name, address and phone number of your chosen lab with your treatment papers. If a relative arranges a test while you are unwell, they can use the same lab rather than the nearest one, keeping your results consistent.

Emergency tests are different

In an emergency, tests will be done wherever you are treated. That is the right choice. Share those reports with your team afterwards so they can be compared sensibly.

What to do next

Choose one accredited lab your team trusts, keep sample timing consistent, keep complete reports with units and ranges, tell your team whenever you change labs, ask them to explain any results that seem to disagree, and act on symptoms without waiting for reports.