Can Blood Test Results Vary Between Different Laboratories?

A vital element of private blood tests that makes them useful to individuals and companies alike is interpretation of the results, and a key element to this is to understand the role variation plays in any type of test.

Many blood tests are undertaken multiple times, sometimes using several laboratories, systems of analysis and methods of collecting samples in order to generate the clearest picture possible of a person’s overall health or specific biomarkers.

This biological variation is a known phenomenon and is accounted for by doctors, but to understand why, it is important to know why blood tests vary, how much of this is based on the person being tested and how much is based on the equipment, 

Why Do Blood Tests Vary Between Laboratories?

When it comes to blood, no two tests will produce the exact same results, as even the slightest change in approach, methodology or the handling of blood samples can cause the results to shift slightly.

There are countless different factors depending on the types of tests that have been requested, but here are the most critical variables.

Human Biology

The time of day, everything you eat and how much you drink can affect various biomarkers in your blood, as can stress, illness and hormonal cycles.

All of this will affect test results, sometimes dramatically, which is why the pharmacy, clinic or laboratory taking your test might ask you to fast or abstain from certain foods for a day or more before your test.

Environment

Humidity and temperature can cause subtle changes to the reagent reactions used in testing, particularly during extreme weather conditions.

This means that a test result may be different on a rainy day than a sunny one, due to changes in humidity levels and lab temperatures.

Calibration of Instruments

Precise instruments are calibrated to a particular set of reference tolerances, which can in some cases be subtly different in different laboratories or when used by different researchers.

These variations are minuscule, but they do exist.

Variation In Reagents

Reagents are typically manufactured in batches, and whilst they are made to restrictive tolerances, there are minor differences between some test results.

Sample Handling

How a sample is collected, when it is collected, what temperature it is stored at, and the entire system of processing definitionally cannot be the same between laboratories, and this accounts for the same blood test producing different results.

How Do Laboratories Account For Variation?

Most laboratories use a tolerance system known as a reference change value to determine the range of test results that fall within an accepted set of variables.

If two tests are different but fall within the RCV, they are typically treated as normal, but anomalous test results which cannot be accounted for through confounding factors often require further examination and testing, as it could be indicative of a problem.

What Should You Do If You Are Worried About Different Test Results?

Ultimately, if you are worried about any of the tests you receive, talk about them with your doctor, the doctor who requested the test or the laboratory which produced them for you and ask about the results.

If you are still unclear, requesting another test can sometimes provide additional clarity.