You sleep eight hours and still wake up wrecked. Your coffee carries you until about eleven, then you crash again. Persistent fatigue feels vague, but it often has a measurable cause. The most common are iron deficiency, an underactive thyroid, a shortage of vitamin B12 or vitamin D, and hormonal changes around the menopause. A few blood values usually give quick direction.
In my experience, women often muddle through fatigue for months before getting tested. That is a shame, because with fatigue a blood value is one of the simplest starting points. Below you will read which causes are most common and which value fits which pattern.
Why am I always tired?
Tiredness that does not lift 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 blood but still matter.
Women have a few extra risk factors. Menstruation costs iron, pregnancy depletes stores, and around menopause your hormones change. So iron deficiency and thyroid complaints are more common in women than in men. On Thuisarts.nl, the public information of the NHG (Dutch College of General Practitioners), it states that with prolonged tiredness it is logical to have a few blood values checked.
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.
| What you notice | Possible direction | Value that gives insight |
|---|---|---|
| Tired, pale, short of breath 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, especially in winter | Vitamin D deficiency | Vitamin D |
| Tired, hot flushes, irregular cycle | Menopause | FSH + oestradiol (hormone panel) |
| Tired, tense, sleeping poorly | Prolonged 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 one of the most common causes 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 often already feel exhausted.
That distinction is often missed. A low ferritin without anaemia can explain many complaints that otherwise stay unexplained. The NHG anaemia guideline describes how ferritin and haemoglobin are read together. The Iron Status measures ferritin and iron, among others, in one draw.
A practical rule of thumb: if you have heavy periods, recently gave birth or eat little or no meat, your iron store is a logical first suspect for unexplained tiredness.
Thyroid: a quiet spoiler
An underactive thyroid (hypothyroidism) can slow your whole system. Fatigue, cold, weight gain and slow thinking can fit, and the complaints develop so gradually that they are easily put down to a busy life.
Want to know when your thyroid is the cause? Read our article on thyroid and fatigue, or the overview thyroid symptoms in women. 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 especially in the dark months.
Vegetarians, vegans and women using acid-reducing medication have a higher risk of a B12 deficiency. The B Vitamins measures B12 and folate, among others. The Gezondheidsraad (Health Council of the Netherlands) advises women from age seventy, and people with darker skin or little sunlight, to take vitamin D; a measurement shows whether your vitamin D is genuinely low.
Menopause and hormones
Around the menopause your hormone balance changes, 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 can be useful to look at several causes at once.
Unsure whether your complaints fit the menopause? Read our article on navigating perimenopause, or look at the Menopause test that measures the menopausal hormones.
Stress and cortisol
Prolonged stress drains your energy and disrupts your sleep, which further deepens the tiredness. Cortisol, your main stress hormone, can then fall out of rhythm. A measurement does not replace a conversation about your lifestyle, but can help separate stress from a physical cause. Read more about cortisol and chronic stress.
One cause or several at once?
The treacherous thing about fatigue in women is that causes often occur together. A woman in perimenopause with heavy periods may have both a low ferritin and a shifting hormone balance. A vegan with a busy job might combine a B12 deficiency with too little sleep. One value then rarely explains the whole picture.
So a good review looks at the pattern, not at loose numbers. A low-normal ferritin that on its own falls "within range" can still contribute to your complaints if other values are also on the low side. It is exactly this interplay that a doctor weighs, and that a single self-test or loose measurement misses.
What if several deficiencies are present at once?
If your result shows more than one abnormality, that is not cause for panic, but it is reason to decide on priorities. Not all deficiencies are equally serious, and not all respond equally quickly to supplementation. A few starting points that help you keep an overview:
- Start with the deficiencies that are most quickly correctable and cause the most trouble. A significant iron deficiency with heavy periods often needs more immediate attention than a vitamin D that sits just below the threshold in the summer months.
- Vitamin B12 and iron deficiencies sometimes depend on each other. B12 plays a role in the production of red blood cells; a combined deficiency can cause anaemia that responds more slowly to iron supplementation alone.
- Supplementation is tailored work. Taking too much iron is not without risk, and with vitamin D too, more is not always better. Have your GP guide you here, especially if you are addressing several deficiencies at once.
- Schedule a repeat test after three to four months. That way you can see whether your ferritin or vitamin D genuinely recovers, and whether you have missed any other deficiencies.
The goal is not a perfect number on paper, but that you start feeling better. Both things together are not a given: sometimes a value improves while the tiredness persists, and sometimes you feel much better before a value has fully recovered. That is not reason to stop, but it is reason to keep consulting your doctor.
When is extra guidance needed?
A blood test gives direction, but there are situations where it is better not to wait for the result to explain everything. See your GP if your tiredness comes with unexplained weight loss, fever, persistent paleness or shortness of breath at normal activity. Also if your result shows a significant deficiency or a strongly abnormal value, it is wise to consult a doctor before you start supplementing. Anaemia from a B12 deficiency sometimes requires injections rather than tablets; your GP makes that distinction based on your result and your complaints together.
If you are pregnant or trying to conceive, this applies even more: iron and folic acid have specific targets in that period that differ from the regular reference values. Always get guidance in that case.
How often is testing useful?
For a first exploration of persistent tiredness, one measurement of the core values usually suffices. If you find a deficiency and adjust, a repeat measurement after a few months can show whether the approach works, for example whether your ferritin or vitamin D recovers. The NHG guidelines advise repeating mainly guided by your complaints and earlier results, not on a fixed calendar. Discuss with your GP which rhythm suits your situation.
When is a blood test useful?
A test is most useful if your tiredness lasts longer than a few weeks and does not lift with rest. A measurement then gives quick direction: is a deficiency behind it, or should you look elsewhere?
- You have been tired for weeks, even after enough sleep
- You have other complaints alongside tiredness, such as paleness, cold or tingling
- You have heavy periods or recently gave birth
- You recognise menopausal complaints and want to rule out other causes
At Lunara you test without a referral at a location near you, and your result gets a per-value review from a BIG-registered doctor. So you know not only your ferritin or TSH, but also what that may mean in your situation.
How do you read a result for fatigue?
A result only gains meaning alongside your complaints and the lab's reference range. A low-normal ferritin may feel fine for one woman and already cause tiredness in another, especially with heavy periods. So a doctor looks not only at whether a value falls inside or outside the range, but also where within that range it sits and whether it fits what you feel.
A few common patterns: a low ferritin with a normal haemoglobin can point to a starting iron deficiency before there is anaemia. A slightly raised TSH with a normal free T4 falls in a grey area that often calls for a repeat. And a vitamin D at the lower limit is so common in winter that the result mainly helps to adjust in a targeted way. None of these patterns is a diagnosis in itself; they give direction for the conversation with your doctor.
What you can do while you wait
A blood test is a snapshot, not an end point. While you wait for your result, it helps to get a few basics in order, so you will know whether your complaints truly come from a deficiency or (partly) from your lifestyle.
- Keep a steady sleep rhythm and watch the number of hours you actually sleep, not just time in bed.
- Eat regularly and enough, with attention to iron sources if you eat little meat. The Voedingscentrum (Netherlands Nutrition Centre) gives practical guidance on iron in food.
- Move a little daily, even when tired: light activity often gives more energy than rest.
- Note your complaints and when they are worst, so you can give a complete picture when your result is reviewed.
If your complaints do not improve, your result together with these observations gives your doctor a far better starting point than tiredness alone.
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 deficiency or menopausal complaints. So it can be useful to look at several values at once rather than one.
What if all my values are normal?
Then that is also valuable information. It points attention to sleep, stress, exercise or nutrition. Always discuss persistent tiredness with normal values with your GP.
Sources
- NHG Guideline Anaemia. Dutch College of General Practitioners. Available via nhg.org.
- Gezondheidsraad. Dietary reference values for vitamin D. The Hague: Health Council of the Netherlands. Available via gezondheidsraad.nl.
- Thuisarts.nl, I am tired. Dutch College of General Practitioners. Available via thuisarts.nl.
Every blood test result via Lunara includes a professional review by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
If your result is already in, the blood value checker places each value in its reference range.
Author
Lunarahealth
Dr. Naimi, BIG-registered physician, oversees the medical standards behind our content and assessments. Read our medical policy
