4 / Fatigue Blood Tests: What Is Actually Worth Checking?

You have worked on your sleep. You are eating properly. You have stopped trying to survive on coffee, you are moving your body and giving yourself enough recovery. But you are still exhausted.

This is where I want us to stop guessing. Persistent fatigue deserves investigation, but that does not mean ordering every biomarker available. The purpose of testing is to answer a much more useful question: What could be interfering with my body's ability to produce energy, transport oxygen, regulate metabolism or recover properly?

Start with a full blood count

A full blood count, or FBC, is one of the most useful starting points in persistent fatigue. It measures haemoglobin, red blood cells and several characteristics of those cells, as well as white blood cells and platelets.

Low haemoglobin indicates anaemia, which reduces the blood's capacity to transport oxygen. That can leave you exhausted, breathless on exertion, weak or struggling with exercise that previously felt easy. The size and characteristics of your red blood cells can also provide clues about what may be causing anaemia. Iron deficiency, B12 or folate deficiency, chronic disease and other conditions can produce different patterns.

But there is an important limitation. A normal haemoglobin does not necessarily mean your iron status is fine.

Ferritin matters, especially if your periods are heavy

Ferritin gives us information about the body's stored iron. This matters enormously in perimenopause because menstrual bleeding can become heavier or more prolonged. You can gradually deplete your iron stores before haemoglobin falls sufficiently to classify you as anaemic.

In other words, iron deficiency and iron-deficiency anaemia are not the same thing. Fatigue can occur with iron deficiency even without established anaemia.

Ferritin needs context, however. It is also an acute-phase protein and can rise during inflammation, potentially making iron stores appear better than they really are. When the picture is unclear, a fuller iron assessment may include serum iron, transferrin or total iron-binding capacity and transferrin saturation, interpreted alongside ferritin and the full blood count.

And if iron deficiency is found, don't stop at the result. Ask why. Heavy menstrual bleeding is one possibility. Gastrointestinal blood loss, low intake and impaired absorption are others. Correcting iron without addressing ongoing blood loss is only solving half the problem.

Check your thyroid rather than assuming it is menopause

Hypothyroidism can cause fatigue, cognitive slowing, cold intolerance, constipation, dry skin, hair changes, muscle symptoms and changes in weight. You can see why it gets confused with menopause.

For most adults with suspected primary thyroid dysfunction, TSH is the appropriate starting test. If TSH is elevated, free T4 helps determine whether hypothyroidism is present and how significant it is. Additional thyroid testing can be appropriate when the initial results or clinical history justify it.

One useful detail if you take supplements: high-dose biotin can interfere with some thyroid laboratory tests and produce misleading results, so tell your healthcare professional what you are taking before testing.

Look at glucose regulation

Glucose problems can also contribute to fatigue, so I want to know more than whether you ate sugar yesterday. Fasting glucose shows your blood glucose concentration at that particular fasting moment, while HbA1c reflects average glucose exposure over approximately the previous two to three months and is widely used to screen for and diagnose prediabetes and diabetes.

But metabolic dysfunction develops along a continuum. As tissues become less sensitive to insulin, the pancreas may compensate by producing more insulin to keep glucose controlled. This means fasting glucose and HbA1c can remain within reference ranges while the metabolic environment is already changing.

This is why I sometimes consider fasting insulin alongside glucose, particularly when there are other clues such as increasing abdominal fat, high triglycerides, low HDL, hypertension, previous gestational diabetes, PCOS or a strong family history of type 2 diabetes. But fasting insulin is not a standalone diagnostic test for fatigue or insulin resistance. It is another piece of the metabolic picture.

Vitamin B12 deserves proper interpretation

Vitamin B12 deficiency can cause fatigue, but its effects extend far beyond energy. B12 is required for normal blood-cell production and nervous-system function. Deficiency can contribute to cognitive changes, numbness or tingling, balance problems and neurological symptoms as well as fatigue.

Importantly, B12 deficiency can exist without anaemia or enlarged red blood cells, so a normal full blood count does not always exclude it. Risk is higher with certain dietary patterns and conditions that interfere with absorption, including autoimmune gastritis, gastrointestinal surgery and some medications. Metformin and proton-pump inhibitors are among the medications that can increase the risk.

Initial testing generally uses total serum B12 or active B12. If the result is borderline and clinical suspicion remains, additional testing such as methylmalonic acid, or MMA, can sometimes help clarify whether true deficiency exists.

There is another practical problem. Taking B12 supplements before testing can increase the measured blood concentration without necessarily resolving an underlying deficiency, which can complicate interpretation. So ideally, investigate before throwing supplements at the result.

Folate belongs in the picture when indicated

Folate works closely with B12 in DNA synthesis and normal red blood cell production. Deficiency can contribute to megaloblastic anaemia and fatigue, and folate testing can be useful when the blood count, diet, alcohol intake, gastrointestinal history or symptoms suggest a problem.

But I don't automatically test folate in every tired woman. Again, testing should follow the clinical picture. Significant folate supplementation should also not become a substitute for checking B12 when B12 deficiency is possible, because the two deficiencies can overlap while the neurological consequences of B12 deficiency require proper recognition.

Vitamin D is important, but fatigue alone is not enough to diagnose deficiency

Vitamin D is essential to bone and mineral metabolism and also plays roles in muscle and immune function. Low vitamin D status is common in many populations, but fatigue is extremely nonspecific. You cannot diagnose vitamin D deficiency because somebody feels tired.

Testing 25-hydroxyvitamin D is most useful when there are risk factors for deficiency, bone-health concerns or other clinical reasons to assess it. If deficiency is found, correct it appropriately. But I would not chase increasingly high vitamin D concentrations in the hope that more automatically means more energy. It doesn't.

Check kidney function and electrolytes

Your kidneys do far more than produce urine. They regulate fluid balance, electrolytes and acid-base balance, remove metabolic waste and produce signals involved in red blood cell production.

A basic biochemical assessment can therefore add important information in unexplained fatigue. Depending on the laboratory, this may include creatinine and estimated glomerular filtration rate, or eGFR, sodium and potassium, with additional markers according to the clinical situation. Abnormalities here can sometimes point us away from "menopause fatigue" and toward a completely different problem.

Include liver function in persistent unexplained fatigue

The liver is central to metabolism, nutrient processing, glycogen storage, protein synthesis and the metabolism and clearance of many hormones and medications. Common laboratory markers include ALT, AST, GGT, alkaline phosphatase and bilirubin.

These tests can identify patterns suggesting liver or biliary disease, although normal liver enzymes do not guarantee perfect liver health. I would interpret them alongside alcohol intake, medication, metabolic health, triglycerides, glucose regulation and other risk factors rather than looking at one enzyme in isolation.

What about inflammation markers?

This is where I would resist the temptation to test simply because we can. Markers such as CRP or hs-CRP can provide information about inflammation, but they do not tell us what is causing it.

An elevated CRP can occur with infection, inflammatory disease, tissue injury and many other conditions. hs-CRP can also be useful in cardiovascular risk assessment in particular situations. Neither test diagnoses the cause of fatigue.

If symptoms or medical history suggest an inflammatory or autoimmune condition, inflammatory markers may become useful as part of a targeted investigation. But "I am tired, therefore check my inflammation" is not enough of a clinical question.

What about cortisol?

Cortisol is another test that has become almost synonymous with fatigue online. Cortisol is an essential adrenal hormone involved in the stress response, blood pressure, immune regulation and glucose metabolism.

But random cortisol testing is not a general fatigue test. If symptoms suggest genuine adrenal insufficiency, such as significant unexplained weight loss, low blood pressure, dizziness, gastrointestinal symptoms, salt craving or abnormal electrolytes, adrenal function deserves proper medical investigation.

That is very different from ordering a multi-point cortisol panel because you feel depleted after a stressful year. Chronic stress can absolutely contribute to exhaustion. It does not automatically mean your adrenal glands are failing.

Do I need my menopause hormones checked because I am tired?

Usually, fatigue alone is not a good reason to order a reproductive hormone panel. As we covered in our Hormones and Menopause series, FSH and estradiol fluctuate considerably during perimenopause, and in women over 45 with typical menstrual changes and symptoms, perimenopause is usually recognised clinically.

Progesterone, testosterone and DHEA-S also have specific clinical uses, but none is a general "energy marker." A low progesterone result taken at the wrong point in the menstrual cycle tells us little. A testosterone result does not diagnose the cause of fatigue. DHEA-S naturally changes with age and is not a routine test for menopausal tiredness.

If there is a genuine endocrine question, test it. But don't turn fatigue into an excuse to order every hormone the laboratory offers.

And what if all my fatigue blood tests are normal?

This is perhaps the most important section of the article. Normal blood tests do not mean your fatigue isn't real. Blood tests only investigate the things blood tests can measure.

If you wake exhausted despite spending enough time asleep, especially if you snore, wake gasping, experience morning headaches or have significant daytime sleepiness, think about obstructive sleep apnoea and whether a sleep assessment is needed. Persistent insomnia can cause profound fatigue despite immaculate blood results.

Medication can contribute. Depression and anxiety can present predominantly as physical exhaustion. Chronic pain can be exhausting. Cardiovascular or respiratory problems may present with reduced exercise tolerance. And some illnesses require investigations that extend far beyond the basic blood panel.

This is why indiscriminately ordering dozens of tests often doesn't solve persistent fatigue. The next question after normal blood work should therefore not automatically be "What else can I test?" It should be: What does my pattern of symptoms tell us to investigate next?

So what would I actually check?

For persistent unexplained fatigue, a sensible starting assessment may include a full blood count; ferritin, with fuller iron studies when indicated; TSH, with free T4 according to the result and clinical picture; fasting glucose and HbA1c, with fasting insulin where it adds useful metabolic information; vitamin B12, with additional testing such as MMA when indicated; folate where appropriate; vitamin D when deficiency risk or clinical circumstances justify testing; renal function and electrolytes; and liver function.

Additional investigations should then be selected according to symptoms, examination, medical history, medications and risk rather than automatically adding more biomarkers.

What I want you to take away from this series

Fatigue after 45 is common, but common does not mean something you simply have to accept. First understand what kind of fatigue you have, then address the obvious drains on energy, rebuild sleep, nutrition, muscle, metabolic health and recovery, and investigate persistent symptoms rather than masking them with caffeine or supplements.

Most importantly, don't assume menopause explains everything and don't assume normal blood work means nothing is wrong.

Fatigue is information. The goal is not to silence it. It is to understand what it is telling you.

You can explore more articles, free and paid resources, my book and programmes in the Energy & Fatigue section of Feel Good Menopause.