Why Do I Need A Repeat Blood Test
General, Tests & Procedures

Reasons For Repeat Blood Tests

Have you ever been in a situation where you had your blood tests done and were asked to repeat the blood tests? Most of us get startled and are confused when we are asked to retake the tests as no specific reason is given by the medical practitioner. This is when we are left with questions like, why do I need a repeat blood test?

Well, in this article let us try and understand a few possible reasons for a second blood test.

Why Do I Need A Repeat Blood Test?

Clinical Errors

The clinical laboratories that operate around the globe have the policy to follow. A policy that asks for repeat test results which occur due to unexpected values for a particular patient. This happens when the values obtained from the first test show an analytical error. That is corrected by taking a re-test. Though the use of technologically advanced testing equipment reduces the chance of such errors. They still happen in various clinical laboratories.

So, the next question that arises here is that irrespective of using “highly automated clinical chemistry laboratories”, is repeating a blood test really necessary? As per a study conducted in the United States of America,

About 3% of The Total Test Reports Often Need A Re-Testing

This occurs when the results are outside the predetermined limits. Such analytical errors occur when the initial and the re-test values exceed the given “error limit”.

Due To False Positive Test Results

Reasons for having a blood test again can be many. In a number of cases, the screening that is conducted for one condition has for sure has to be confirmed by another test. This is important as it helps the doctor to be sure about the results obtained and the course of the treatment is defined based on the results obtained from both the tests. This not only applies to blood tests but is also followed when other tests are done. It is to know about the underlying disease.

False Negative Test Results

There are times when the blood test does not show the evidence of an illness or a disease, even when the patient has it. For example, if you underwent a test for hepatitis C and the results came out to be negative, the doctor might ask you to retake the test as you were exposed to this virus earlier. There are chances that you might have an infection but the results are not yet showing the same.

Also, when you get yourself tested for something like a Lyme disease within the first 1 -2 weeks, the test results might come as negative. This is when you might have to repeat the blood test in 2 weeks.

Your doctor might also ask you to repeat blood test for kidney function. This happens even when the tests come positive as the doctor needs to make sure that the results obtained are accurate. It is said that three blood test results that are positive over a period of three months are the sign of a kidney disease. The blood test in such cases is done to check for a waste product called as Creatinine.

Abnormal Test Results

One of the other reasons why you might have to repeat a blood test is when the test result is outside the actual or the normal range of the lab values that were expected for that particular illness. The reasons for the change in the test results can be many. You might have undergone a fasting glucose test but you happened to eat something just before it or the results might even vary if you have consumed alcohol the night before. Even taking medications before giving the blood samples can show abnormal blood test results.

So, in order to avoid such issues, the doctor might ask you to go for a retest. It is just to make sure the test results are accurate. If you wish to avoid it, you can as well talk to your doctor about the precautions to be taken before you give your blood sample.

Mistakes With Handling

Though the mix-ups of blood samples is a very rare scenario, it does happen at times. How the blood sample gets handled before being checked can change the results drastically. Like for example, if the blood samples are shaken badly or even stored for a longer time or at a wrong temperature, the test results will vary.

Guess you might have found an answer to your question, “why do I need to repeat a blood test”. Hence do not panic when your doctor asks you to retake the blood test that you have just taken.

Medically Reviewed By
Dr. Kaushal M. Bhavsar (MBBS, MD)Assistant Professor in Pulmonary Medicine, GMERS Medical College, Ahmedabad