Blood Tests

Why Do Blood Test Results Vary With Different Labs?

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Are you waiting for the result of your blood test and wondering if it will be reliable? Or are you considering getting your blood tested at some other lab? There are many clients who send us the questions related to blood test results and without a doubt, the question is important enough.

Our users are surprised many times regarding the blood test results varying between labs to labs. It doesn’t depend on the academics of different labs but it is solely dependent on the different time points, some other variations, and importantly the calibration of different equipment at labs.

Would the different blood test results make any difference? Or cause more doubts?

First things first. Yes, the result of blood tests done in the same method and conditions from different labs can be very similar but not the same.

Results of blood tests are often given in the numbers or statistics or a simple yes or no. In the case of a test done for any particular inflammation or disease, the result is yes or no.

Generally, the results are quite similar in the laboratories that use the same blood test method and the sample type but this isn’t the case always. Because the reference range differs from lab to lab.

Statistical or numerical results are not of much importance until they are interpreted. And the results are interpreted by the help of a reference point. This is where the results will start to differ.

Reference values

Reference values are a set of values that are made into consideration to a healthy person and the results are compared to the reference points to draw out the conclusion.

Reference points are fairly to be different for every other lab. Reference values are as a guide to form conclusions about the health of the person.

The reference range also depends on the people who took the test to set up the reference values. Do not forget reference values are not normal values.

Types of equipment

Every lab has different types of equipment with which they collect samples and test blood. It is bound to have a different result because the equipment affects the results. Be it from the storage container in which blood is stored or the equipment under which it is tested.


Analytical work is bound to have issues and errors. These tests if performed repeatedly in the same lab can cause a lot of difference let alone different labs. The blood test involves chemically testing blood under chemicals and pigments which reacts differently in some cases. The potency of the chemicals can cause variance in the result of the blood test result. For example, vitamin B12 is known to be a test that is not always precise.

Diet and hydration of the patient

If the tests are done on different days results can vary due to differences in hydration and glucose levels in the body. If the diet of the patient has varying vitamin K levels it can be highly affected by Coumadin, the blood thinner drug, which is used by many patients.

Over-hydration is also one of the factors which affect the result of the blood test.

Test methods

The test methods or procedures used to test the blood can also cause variation in the result of the blood test. Different procedures involve different chemicals, routine, time intervals which are bound to have different reactions in blood tests.

Some methods are just incompatible in nature. Like enzyme, LDH can be measured using either forward lactate which pyruvate the reaction or reverse pyruvate which causes lactate change.

Sample handling

A simple step that is generally not paid attention to. It is an important step because how the sample has been retrieved and handled till and during the test can cause variance in the blood test result. Samples that are not true as they were taken can cause a major difference in the result.

Systematic errors

There can be errors in techniques, poor calibration, or even imbalance between methods. Immunological techniques can be difficult to cooperate as the antibodies used by different labs is varying mainly due to labs often get their antibody agents patented and labs avoid using the same antibody.

Also Read, ESR Blood Test – The Detector of Causes of Inflammation in a Human Body


It is a whole different problem. Like urate test can be measured in two ways.

One method is by using a chemical method that involves phophotungstate or the enzymic method which involves uricase. Both of these easily interfere with Vitamin C. The interference is also different; positive in case of plasma and negative in case of an enzyme. 

Other factors which can cause variation of results can be:

Use of valid reagents.

Daily calibration error.

Inexperienced hands or human error.

Interval of sample taking and actual testing.

Dr. B. Lal Clinical Laboratory Pvt. Ltd. was established in 1991 with a motive of Serves Best, Serves All and since then it has been working uninterrupted to provide Pathological and Diagnostic solutions that incorporate the best infrastructural and technological advancements in the world of the health sector. Our passion is to deliver the best quality healthcare services combined with the uncompromised trust shown by doctors and patients in our services have made us a distinguished preference over the last 30 + years.

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