Persistent fatigue often has a measurable cause. The most common are an iron deficiency, an underactive thyroid, a shortage of vitamin B12 or vitamin D, and hormonal changes around menopause. A few blood values usually give quick direction.
I notice that women often push through tiredness for months before having blood drawn. That is a shame, because with fatigue a blood value is one of the simplest leads. Below you read which causes are most common and which value fits which pattern.
Why am I always tired?
Tiredness that does not pass with rest rarely points to one thing. Often several factors play a part: your iron stores, your thyroid, your vitamins and your hormones. Sleep, stress and exercise also count, which you do not see in the blood but which still matter.
Women have a few extra risk factors. Menstruation costs iron, pregnancy drains stores, and around menopause your hormones shift. So iron deficiency and thyroid complaints are more common in women than in men.
Which blood values give insight for fatigue?
No single value explains tiredness on its own. But a few core values together show where to look. The table below links a pattern of complaints to the value that usually says the most about it.
| What you notice | Possible direction | Value that gives insight |
|---|---|---|
| Tired, pale, breathless on exertion | Iron deficiency or anaemia | Ferritin + haemoglobin |
| Tired, cold, weight gain, slow thinking | Underactive thyroid | TSH + free T4 |
| Tired, tingling, forgetful | Vitamin B12 deficiency | Vitamin B12 + folate |
| Tired, low mood, especially in winter | Vitamin D deficiency | Vitamin D |
| Tired, hot flushes, irregular cycle | Menopause | FSH + oestradiol (hormone panel) |
| Tired, tense, poor sleep | Long-term stress | Cortisol |
This table is an aid, not a diagnosis. Often it is the combination of values that completes the picture. Which ones are useful for you depends on your complaints and history.
Iron deficiency: the most common cause in women
Iron deficiency is the most common cause of tiredness in women. Your ferritin, the iron store, can already be low while your haemoglobin is still normal. You are then not yet anaemic, but you often already feel drained.
That distinction is often missed. A low ferritin without anaemia explains many complaints that otherwise stay unexplained. So also read our article on iron deficiency without anaemia, and on how to prevent iron deficiency with nutrition and supplements. The Iron Status measures ferritin and iron among others in one draw.
Thyroid: a quiet spoiler
An underactive thyroid (hypothyroidism) slows your whole system down. Tiredness, cold, weight gain and slow thinking fit it, and the complaints develop so slowly that they get blamed on a busy life.
Thyroid problems are five to eight times more common in women than in men (Taylor et al., 2018). Want to know when your thyroid is the cause? Read our article on thyroid and fatigue. The Thyroid Complete measures TSH, free T4, free T3 and anti-TPO.
Vitamins: B12 and vitamin D
A shortage of vitamin B12 or vitamin D often gives a vague, creeping tiredness. B12 plays a role in your energy and nervous system; a shortage can also cause tingling and forgetfulness. Vitamin D drops in the Netherlands mainly in the dark months.
Vegetarians, vegans and women who use stomach-acid inhibitors have a higher risk of a B12 deficiency. The B Vitamins measures B12 and folate among others. A vitamin D deficiency is so common in autumn and winter that a measurement is then often useful.
Menopause and hormones
Around menopause your hormone balance shifts, and fatigue is one of the most reported complaints. The tricky part is that menopausal tiredness looks strikingly like tiredness from the thyroid or from anaemia. So when in doubt it is useful to look at several causes at once.
Unsure whether your complaints belong to menopause or come from elsewhere? Then read our article on menopause or burnout, and on the first signs of perimenopause.
When is a blood test worth doing?
A test is mainly worthwhile if your tiredness lasts more than a few weeks and does not pass with rest. A measurement then quickly gives direction: is a shortage behind it, or should you look elsewhere?
Consider testing if you recognise this:
- You have been tired for weeks, even after enough sleep
- You have other complaints alongside tiredness, like paleness, cold or tingling
- You have heavy periods or gave birth recently
- You recognise menopause complaints and want to rule out other causes
At Lunara you test without a referral at a location near you, and your result gets an assessment per value by a BIG-registered doctor. So you know not only your ferritin or TSH, but what it can mean in your situation.
Frequently asked questions
Which blood test do you do for fatigue?
It often starts with ferritin, haemoglobin, TSH, vitamin B12 and vitamin D. Together these cover the most common causes. Which combination suits you depends on your complaints.
Can fatigue have several causes at once?
Yes, and that is often the case. A low ferritin can go together with a vitamin shortage or menopause complaints. So it makes sense to look at several values at once rather than one.
What if all my values are normal?
Then that is valuable information too. It shifts the focus to sleep, stress, exercise or nutrition. Always discuss persistent tiredness with normal values with your GP.
References
- Taylor PN, Albrecht D, Scholz A, et al. Global epidemiology of hyperthyroidism and hypothyroidism. Nat Rev Endocrinol. 2018;14(5):301-316. PMID: 29569621.
- NHG-Standaard Anemie. Dutch College of General Practitioners. Available via nhg.org.
- Health Council of the Netherlands. Dietary reference values for vitamin D. The Hague. Available via gezondheidsraad.nl.
- NHG and Thuisarts.nl. Tiredness. Dutch College of General Practitioners. Available via thuisarts.nl.
Every blood test result through Lunara includes a professional assessment by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
Tagi
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