5 Lab Tests If You’re Feeling Tired


If you've ever suffered from fatigue, you know it makes life pretty miserable. You also probably know the difference between feeling tired and feeling fatigued. And if you've ever suffered from chronic fatigue, you know that it can make your life more challenging than it should be. 

Simple, routine tasks start to become overwhelming, things that you used to love doing start to feel like too much work, and then you start to beat yourself up for feeling lazy even though you know that isn't really what is going on. I remember when my fatigue was it it's worst, practically crawling up the stairs after a 30 minute run on several occasions and collapsing on the couch for a multiple hour nap (and this was not at all normal for me). Or feeling like the relatively simple act of cooking dinner was more than I could handle. Feeling this way makes for a pretty miserable existence. 

The unfortunate part of fatigue is that sometimes there's a simple answer and solution and sometimes there is not. Sometimes it's like peeling away the layers of an onion to get to the bottom of what's causing it and other times it can be a relatively simple fix like really dialing in your diet and other lifestyle factors. 

If you've talked to your healthcare practitioner about feeling fatigued, they probably ordered a TSH lab test to check your thyroid and maybe a few others. There are a few other tests that you might want to consider getting too, especially if you are eating a nutrient-dense diet, have optimal thyroid function, but still feel like you are moving through molasses or can't make it through the day without a nap...or three. 

Feeling Fatigued or tired? Here are 5 lab tests you should consider

Vitamin D

Vitamin D is important to your energy levels. Mitochondria are the structures inside your cells that are responsible for manufacturing ATP, which is your body's main source of energy.  Researches at Newcastle University found that low vitamin D levels correlated with suboptimal mitochondrial function. They also found that the mitochondrial function of those who were deficient in vitamin D improved significantly after vitamin D supplementation. The improvement in the ability of the mitochondria in these people correlated with increased vitamin D levels and improved energy levels. 

If you are an athlete, vitamin D is even more important as it may also affect muscle strength. A group of Australian researchers found that muscle strength improved in the 30 vitamin D deficient patients they had in their study. 

Optimal vitamin D levels are 60-80 ng/dl, but according to the Institute of Medicine, anything above 20 ng/dl is "appropriate." 

Vitamin D is also important in immune system function which can indirectly affect your energy levels. 

Iron studies

Both low and high iron levels can cause fatigue. 

Checking iron levels indirectly via your hemoglobin levels in a complete blood count (CBC) is fairly standard practice in patients who report fatigue. While iron deficiency and iron deficiency anemia are far more common, excess iron (also called hemochromatosis) may also be a concern. 

Iron plays a role in the formation of hemoglobin, which carries oxygen from the lungs to the rest of the body. Without enough iron, your cells can't function. Cells need two things, at a minimum, to function properly - glucose and oxygen. If they don't have enough oxygen because your hemoglobin levels are low, then they won't work properly. 

In addition to testing hemoglobin, hematocrit, and red blood cells count, you should also consider ferritin (which is the form of iron that can be stored by your body). Testing for B12 and folate levels may also be helpful as low levels of these are also linked to anemia. 

There is some debate over optimal levels of these labs. A "normal" level of B12 is in the 200-900 pg/mL range, but most people feel best when they are up around 800 pg/mL. For ferritin, women should be in the 12-150 ng/mL range, but many experts agree that in order to optimize thyroid health, you should fall in the 90-110 ng/mL range. 

Folate can be deficient if you have the MTHFR gene mutation (see below) which prevents your body from properly absorbing folic acid from supplements. 

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mTHFR mutation

Methyltetrahydrofolate reductase (MTHFR) is an enzyme in that converts folate (B9) into the active form used by the body via a process called methylation. There are several genetic mutations that change how your body makes this conversion and whether it is able to do so effectively. The different genetic variants correspond to varying degrees of loss of this ability. The best way to test for these genetic mutations is to have your healthcare provider order the testing for you. 

chronic infections

There are several studies that indicate that patients who are constantly fatigued have lab markers that indicate they have chronic bacterial or viral infections. In one study of those who had chronic fatigue, almost 80% had markers of a reactivated Epstein-Barr virus (EBV) and 50% had increased antibodies for Human Herpes Virus (HHV). A review of studies found that 50% of patients with chronic fatigue and fibromyalgia were infected with Mycoplasma compared to just 10% of controls. 

Remember that the presence of these infections alone isn't likely to cause disease. Over 95% of the population has been exposed to most of these pathogens but most of those who are infected are not sick. Testing for these infections should be done as a part of a comprehensive workup for fatigue and should be interpreted by a provider who is familiar with this type of testing. 

hormone testing

I prefer to use the Dutch hormone test because it's both comprehensive and, as I said in my podcast episode about adrenal fatigue recovery mistakes, it gives you information about the pattern of things like cortisol (but is more accurate than saliva testing). Cortisol levels that are out of balance can contribute to fatigue, but your sex hormones (estrogen, progesterone, testosterone, and DHEA) also play an important role in your energy levels and mood. Blood testing for hormones isn't particularly helpful, which is why I like the Dutch Test. 


Diamond, T., Wong, Y. K., & Golombick, T. (2012). Effect of oral cholecalciferol 2,000 versus 5,000 IU on serum vitamin D, PTH, bone and muscle strength in patients with vitamin D deficiencyOsteoporosis International, 24(3), 1101-1105. doi:10.1007/s00198-012-1944-7

Hilgers, A., & Frank, J. (1994). Chronic fatigue syndrome: Immune dysfunction, role of pathogens and toxic agents and neurological and cardial changes. Wien Med Wochenschr, 144(16), 399-406. Retrieved May 29, 2018.

Morris, G., Berk, M., Walder, K., & Maes, M. (2015). The putative role of viruses, bacteria, and chronic fungal biotoxin exposure in the genesis of intractable fatigue accompanied by cognitive and physical disability. Molecular Neurobiology, 53(4), 2550-2571. doi:10.1007/s12035-015-9262-7

Sinha, A., Hollingsworth, K., Ball, S., & Cheetham, T. (2013). Improving the vitamin D status of vitamin D deficient adults is associated with improved mitochondrial oxidative function in skeletal muscleEndocrine Abstracts, 3(1). doi:10.1530/endoabs.31.oc1.6