JK Bank
Factors that can affect the accuracy of your blood test results
About Us | Contact Us | E-Paper
Title :    Text :    Source : 

Factors that can affect the accuracy of your blood test results

Physical exercise is one of the most important factors that influence blood test results. Whether you do resistance training, HIIT, yoga, or go for a bicycle ride, this activity could influence some of your blood tests

Post by DR. JAVEED KAKROO on Thursday, September 22, 2022

First slide



Biological Rhythms

Various hormones and other substances in the body have significantly different levels at certain moments of the day. For example, you have different cortisol or testosterone levels in the morning compared with those in the evening. That’s why it’s important to do certain tests at specific moments of the day to ensure the accuracy of the test. Your doctor will usually inform you about that and tell you when it’s the best time for a blood test. Testosterone blood levels peak early in the morning, usually between 7 am, and 9 am. This time of the day is when a testosterone blood test should be done. Throughout the day, testosterone levels slowly decrease, and by evening, they are about two times lower than in the morning. The same story goes for cortisol levels as well. The levels of cortisol in your body peak early in the morning, and they gradually decline by 50%-100% until the end of the day. The time of the month or year is also very important when doing health checkups. For example, getting more vitamin D into your body relies on how much you are exposed to the sun. You can also get supplements with vitamin D if necessary, but sun exposure is one of the best and most efficient ways to get vitamin D. The levels of this vitamin in your bloodstream need to be interpreted based on the time of the year. For example, it’s normal to have the lowest levels of vitamin D during winter times since that’s when sun exposure is limited.



A pregnant woman can also have different test results in comparison with one who isn't pregnant. Pregnancy can change the amount of blood in the body, influence liver hormones, renal function, and other metabolic processes. Changes in hormone levels depend on the pregnancy stage, and they are usually compared against reference values. Physicians can give a pregnant woman more information on how to interpret these results and what they should do about them.


Food and Water

The foods you eat and beverages you drink can influence the results of blood tests. For example, fasting, restricting calories, or being dehydrated can lead to incorrect test results and false diagnosis. To give you an example, a diet rich in protein can lead to increased uric acid levels, and this will be shown in various blood and urine tests. Similarly, a diet which is low in carbohydrates can increase the levels of ketones (ketogenic diet). If a person is a vegan or vegetarian, the levels of vitamin B12 in his/her bloodstream will be low.Some studies have shown that carbohydrates can temporarily decrease testosterone blood levels, so it is important to measure testosterone before breakfast.


Fasting is needed before drawing blood for most blood testing. Patients are usually asked to fast for about 8-12 hours before doing a blood test. Fasting is important when checking lipid levels, blood sugar levels, some hormones, and substances in the body. Not fasting before a CMP test, for example, can lead to an incorrect diagnosis of diabetes type 2 since glucose can be elevated, which is a life-threatening condition if not treated properly. The Lipid Panel test (Triglycerides, LDL and HDL cholesterol) also requires fasting.  Failure to do so may cause the triglycerides value to be higher than normal.


Dehydration also plays a vital role when it comes to blood testing. It can increase blood test values by decreasing the water content of the blood. It can be seen as an imbalance in sodium and potassium levels and lead to false diagnosis. For example, dehydration can affect albumin levels, blood lipids, creatinine (kidney), hematocrit, and some hormones in the body.


Caffeine, Alcohol, and Tobacco

Drinking a lot of caffeine from coffee or green tea can also affect some blood test results. Although more studies are necessary when it comes to caffeine, there is a chance that this substance can alter blood glucose levels and temporarily increase them. Caffeine usually passes through the body in around 5 hours, so its effects are less significant in comparison with other substances. Caffeine can also affect hydration, a factor mentioned above. Last but not least, caffeine can increase blood pressure in some people. The lab technician may be alarmed about your blood pressure before drawing your blood. Alcohol, on the other hand, has a more significant effect on blood tests, depending on how much is consumed and when. For example, this substance might lower serum glucose levels in people of all ages and increase plasma lactate. These changes can happen, especially if alcohol is consumed 2 or 4 hours before drawing blood for testing.


At the same time, chronic alcohol consumption can lead to other problems such as elevated triglyceride levels, elevated creatine kinase levels, elevated liver enzymes, and increased uric acid. As a result, blood tests can be affected, and the doctor could subsequently give a false diagnosis. Frequent alcohol consumption can also lead to mineral and vitamin deficiencies, particularly decreasing the B-complex vitamins. This potential B vitamin deficiency is a concerning problem in chronic alcohol abusers since the vitamins in the B complex are responsible for the proper functioning of the brain and nervous system.

Patients are asked to cease alcohol consumption at least 24-48 hours before drawing blood for testing. This period should give the body enough time to process the alcohol consumed and prevent blood test levels from being affected. However, liver enzymes and triglycerides may not return to baseline in that short period.


Another substance of concern is tobacco, which can also have a profound influence on blood test results. Those who smoke cigarettes have higher levels of nicotine in their bodies. As you probably know, nicotine is a drug which can increase cortisol levels and elevate concentrations of fatty acids in the blood. It may also increase hematocrit (red blood cell proportion, part of the CBC panel) since the body tries to produce more red blood cells to compensate for the lower oxygen level it is getting due to smoke in your lungs. As a result, blood tests can come up with confusing results. Whether cigarette smoking is acute or chronic, it’s detrimental for one’s health, and it can mess up with lab investigations.

Cigarettes also contain thousands of toxins and chemicals which are harmful to the body, including arsenic and cadmium. These can increase the biomarkers of inflammation in the blood and show up in blood tests.



Physical exercise is one of the most important factors that influence blood test results. Whether you do resistance training, HIIT, yoga, or go for a bicycle ride, this activity could influence some of your blood tests. For example, after an intense session of exercise, the levels of creatine kinase (CK) in the body are increased. CK can remain elevated for up to a week, and this will be picked up on blood tests. Different types of exercises can also increase or decrease thyroid hormone blood tests. For example, doing anaerobic exercises can elevate the levels of thyroid stimulating hormone (TSH) in the body. At the same time, anaerobic exercises can also decrease FT3 levels. It is estimated that thyroid hormone levels can be altered for several hours or even several days, depending on the individual and his fitness level. Marathoners are also highly exposed to have altered hormonal levels before and after completing a run. For example, the levels of glucose, albumin, protein, and bilirubin were measured in professional marathoners 4 hours after a run. All these hormones were increased. Studies performed on professional football players who train regularly also reveal that frequent exercise can boost immune function. One study looked at the white blood cell count in 31 males who didn’t do any exercise as well as 32 males who were playing football for a year. The white blood cell count was significantly higher in football players, and this leads to the conclusion that regular exercise can improve the immune response of a person. In another study performed on marathoners, it has been discovered that regular jogging for long periods can reduce the levels of C-reactive protein (CRP), which is a known marker of inflammation. However, excessive running can increase CRP and other inflammatory markers.


When doctors perform an inflammation panel, they test the CRP levels primarily. They want to determine if the inflammation in the body is chronic or acute. Having lower CRP levels as marathoners do helps them avoid chronic inflammatory diseases. On the other hand, some marathoners also had high PSA levels after completing a marathon. PSA stands for prostate-specific antigen, and it’s a marker of prostate disease. 2 out of 21 marathoners had increased PSA levels after running a marathon, which might state a problem with the prostate tissue. However, this can be a false diagnosis since vigorous exercise tends to increase PSA levels in certain people. That’s why doctors recommend performing prostate tests twice if PSA levels are increased as a result of exercise. At the same time, one should wait at least 24 hours after exercise to do a prostate exam to get a more accurate diagnosis.


Last but not least, weightlifting has been shown to result in profound increases in liver function tests in healthy men used to moderate physical activity, not including weightlifting. Liver function tests are significantly increased for at least 7 days after weightlifting. It is important to impose relevant restrictions on heavy muscular exercise prior to and during clinical studies.


(Author is Microbiologist Certified infection control Auditor, Kidney Hospital Srinagar Jkakroo@gmail.com)



Latest Post