Always tired: which blood values should you have tested?

First, some honesty: tiredness is often not visible in your blood

Fatigue is one of the most common complaints in the consulting room, and in the majority of cases no physical cause is found. Too little sleep, prolonged stress, little daylight and exercise, many evenings behind a screen: these are all explanations that no blood test can measure.

If you structurally sleep six hours a night, you should not expect a laboratory result to provide the answer. Side effects of medication, a recent infection or simply a demanding phase of life can also linger for weeks.

At the same time, there is a group of conditions that cause fatigue and are readily measurable in blood:

• iron deficiency
• an underactive thyroid
• a shortage of vitamin B12 or D
• disturbed blood sugar
• low-grade inflammation

Because the complaints of these causes strongly resemble each other, you cannot tell from the outside which one applies to you. That is exactly what a blood test is the right tool for: it replaces guessing with measuring. A blood test is also accessible: one draw, and you know where you stand.

Iron and ferritin: the first suspect

Ferritin reflects your iron stores and is usually the first value to fall when you structurally lose more iron than you take in. Low stores can cause tiredness even before anaemia develops, often together with a shorter fuse, hair loss or restless legs.

Iron deficiency is most common in:

• women who menstruate
• women who are pregnant
• people who eat little or no meat
• dedicated endurance athletes and frequent blood donors, whose stores sometimes decline slowly

Why not simply measure iron itself? Serum iron fluctuates from hour to hour and therefore says little on its own. Ferritin gives a more stable picture of the stores. One caveat: ferritin also rises with inflammation, which means a normal result can sometimes mask a deficiency. Our doctors therefore assess the value in the context of your complaints and, where needed, alongside an inflammation marker.

Thyroid: TSH as the first step

The thyroid drives the metabolism of virtually every organ. When it is underactive, a recognisable pattern tends to follow: persistent tiredness, feeling cold more quickly, weight gain, slower digestion and low mood. The first step is measuring TSH, the hormone that controls the thyroid, usually together with free T4.

At Bloodworks you can have TSH and free T4 measured together as an individual test (€109 all-in) or as part of a broader package. Thyroid complaints often develop so gradually that they only stand out when you look back over the past year.

Vitamin B12 and vitamin D

A vitamin B12 deficiency can cause tingling, numbness in the hands or feet and concentration problems in addition to tiredness. The risk is higher with a plant-based diet and with long-term use of acid-reducing medication or metformin.

Vitamin D plays a role in muscles, bones and immunity; in the Netherlands, stores are low in many people at the end of winter. Both can be measured as individual tests: vitamin B12 for €59 and vitamin D for €69, all-in. If you already take supplements, ideally test before you start, or discuss with a doctor what the result means in your situation.

Blood sugar and inflammation

Blood sugar that is structurally too high or fluctuates strongly can show itself in energy dips, thirst, urinating more often and poor recovery. Fasting glucose (€49 all-in) shows the snapshot; HbA1c (€59 all-in) summarises your average blood sugar over the past two to three months.

CRP (€59 all-in) is the most commonly used inflammation marker: a persistently raised result can explain why your body is burning energy without you noticing, and is a reason for a doctor to look further. Excess weight around the waist, little exercise and diabetes in the family also increase the chance of creeping raised blood sugar; that is exactly when measuring is worthwhile.

How to approach it smartly

Choose your moment deliberately. If you want to know what your body does without help, test before you start taking supplements. If you already take iron, vitamin D or B12, that colours the result; discuss with a doctor what the measurement says in your situation.

Plan the draw on a quiet morning, certainly if you need to be fasted, and combine the tests you want in a single draw: that saves needles and gives the reviewing doctor a more complete picture. If something abnormal is found and you act on it, a repeat measurement after around three months is a common moment to see the effect.

Prefer everything in one go? Fatigue & Sleep

If you would rather not piece together individual tests yourself, the Fatigue & Sleep package is the more logical route. It bundles the blood values that most often give insight with persistent tiredness into a single blood draw, for €189 plus €29 collection fee (free above €225).

You will find the full composition on the product page. The results are reviewed by a doctor and delivered as a clear PDF report, typically within 2 working days of the draw.

Persistent tiredness deserves an honest answer, not assumptions. With a single blood draw you will know within days whether the most common measurable causes play a role for you.

Without a referral, with a personal doctor interpretation and a clear PDF report, and without a subscription. If you are unsure which tests fit your situation, start with the complaint that is most prominent; the overview page with individual tests will point you in the right direction.