Iron deficiency: what a full iron panel can tell you

You're sleeping enough. You're not particularly stressed. But you feel exhausted anyway, the kind of tired that doesn't lift after a good night's sleep. Maybe your hair has been falling out more than usual, or you find yourself short of breath climbing stairs you used to take without thinking.

Low iron is more common in the Netherlands than most people think. When Sanquin started measuring ferritin in every new blood donor, a quarter of first-time female donors already had a ferritin of 30 µg/L or lower , and 5% were below 15 µg/L. RIVM's national food consumption survey finds that girls and women of childbearing age take in too little iron . Yet iron deficiency is also one of the most frequently missed diagnoses in routine care. Not because it's difficult to diagnose, but because the blood markers that reveal early depletion aren't part of a standard blood count, and ferritin is usually only requested when there is a specific reason to.

This article explains what iron deficiency actually means, how it shows up in your body before it leads to anaemia, which blood markers are the most useful, what Dutch guidelines advise, and what the evidence says about different types of iron supplements.

Why iron matters more than most people realize

Iron is not just a component of red blood cells. It is essential for energy production at the cellular level, for thyroid function, for immune response, for cognitive performance, and for carrying oxygen . When your iron stores fall, the effects ripple across multiple systems, which is why the symptoms are so varied and easy to attribute to other causes.

Iron deficiency exists on a spectrum . It starts as iron depletion: your stores are falling, but your red blood cells look normal and function relatively normally. At this stage, you might feel nothing at all or have very mild fatigue , reduced concentration , and hair shedding.

This can then lead to iron-deficient erythropoiesis: iron stores are completely empty, and the iron supply to the bone marrow is no longer sufficient. Red blood cell production is beginning to be impaired, though the cells may still appear normal in size and number on a standard blood count. Haemoglobin may fall within the low end of the normal range. Symptoms become more noticeable at this stage: fatigue, reduced concentration, pale skin and dizziness can appear even before formal anaemia is diagnosed.

The last stage is hypochromic microcytic anaemia: severe, prolonged iron deficiency leading to the production of small (microcytic) and pale (hypochromic) red blood cells. At this stage symptoms may become more severe, including shortness of breath and heart palpitations. This stage is what most standard check-ups are designed to detect.

The first two stages often go unaddressed for months or years, because symptoms can be mild and basic blood panels can appear low but within ‘normal’ range. A standard haemoglobin result may come back within range while stores are already substantially depleted, which is why a more complete panel changes the picture.

How iron deficiency shows up

Symptoms of iron deficiency are easy to overlook because they tend to be gradual and non-specific. The most common include:

• Persistent fatigue that doesn't improve with rest
• Difficulty concentrating or brain fog
• Hair thinning or increased shedding
• Brittle nails, or nails that develop a concave shape
• Cold hands and feet
• Shortness of breath with moderate exertion
• Restless legs, especially at night
• Pale skin, inner eyelids, or gums
• Frequent headaches
• Unusual cravings for ice or clay foods, a phenomenon called pica

Because symptoms are gradual, they are often normalized over time. Fatigue becomes background noise, exercise tolerance drops, and the connection to iron is often only made once levels are actually measured.

Testing for iron deficiency: what the different indicators tell you

A standard complete blood count includes several measurements, but the ones most relevant to iron deficiency are haemoglobin (the concentration of the oxygen-carrying protein in red blood cells), hematocrit (the percentage of blood volume made up of red blood cells), and MCV (mean corpuscular volume, which is the average size of a red blood cell). In the Netherlands, haemoglobin is reported in mmol/l rather than g/dL: the Dutch GP guideline (NHG-Standaard Anemie) uses reference values of 7.5 to 10 mmol/l for women and 8.5 to 11 mmol/l for men. These markers only change once iron deficiency is well established. They will not catch the earlier stages.

To understand where you actually stand, you need a more complete picture.

Serum ferritin is the most important single marker. Ferritin reflects your iron stores, the depot your body draws on when intake is insufficient. Low ferritin is the first sign of depletion , before haemoglobin changes at all. The challenge is that reference ranges in standard labs are set very wide . A ferritin of 12 µg/L can still pass as "normal" by many lab standards, and the NHG guideline sets no fixed cut-off of its own: it relies on each lab's reference range. In September 2026, the American Society of Hematology (ASH) raised the bar: its new guidelines diagnose iron deficiency at a ferritin of 30 µg/L or lower in all adults, including people who menstruate or are pregnant, and at 50 µg/L or lower in people at higher risk, such as those with heavy periods. Sanquin, the Dutch blood bank, already treats a ferritin between 15 and 30 µg/L as suboptimal and pauses donations for six or twelve months while stores recover. Below these levels, symptoms are common even when haemoglobin is normal.

Serum ferritin is also an acute-phase protein , which means it rises during inflammation or infection. This is important: if you have an ongoing inflammatory condition, your ferritin may look normal or even elevated while your iron is actually depleted. Measuring inflammatory markers in parallel, such as hs-CRP and composite indices like SIRI and SII, helps clarify whether a ferritin value is being artificially lifted by inflammation. The new ASH guidelines account for this: with inflammation, for example from inflammatory bowel disease, cancer or an infection, a ferritin below 100 µg/L can already point to iron deficiency. The NHG guideline uses the same 100 µg/L limit for Dutch GPs when there is a chronic illness or a recent infection, read together with serum iron and transferrin.

Serum iron shows how much iron is currently circulating in the bloodstream. On its own it tells you relatively little, because it fluctuates throughout the day (highest in the morning and dropping significantly by the afternoon) and is influenced by recent meals and inflammation. Read together with the next two markers, it becomes informative.

Transferrin is the protein your body uses to transport iron in the blood. When iron stores are low, the body produces more transferrin in an attempt to capture more of the iron that's available. Elevated transferrin alongside low ferritin is a classic early signal of depletion, often visible before haemoglobin moves.

Transferrin saturation is the percentage of transferrin that is actually carrying iron. Low transferrin saturation alongside low ferritin strengthens a deficiency picture, and in the presence of inflammation it can be a more reliable marker than ferritin alone , because it is less influenced by the acute-phase response. With inflammation, ASH considers a transferrin saturation below 20% enough on its own to diagnose iron deficiency.

A thorough iron panel covers at minimum ferritin, serum iron, transferrin, and transferrin saturation, interpreted alongside inflammatory markers when relevant.

Choosing a supplement: food, supplements, and different forms of iron

Getting iron from food first

Before turning to supplements, it's worth understanding what diet can and can't achieve. The Gezondheidsraad (Health Council of the Netherlands) recommends 16 mg of iron a day for women from 18 until menopause, and 11 mg for men and for women after menopause . In the Dutch diet, bread, grains, rice and pasta supply the largest share of iron (26%), followed by meat and meat substitutes (14%) .

Iron from food comes in two forms:

• Haem iron, found in red meat, poultry, and fish, is absorbed efficiently: approximately 25% of the iron in a portion of beef or lamb is taken up by the gut.
• Non-haem iron, found in plant foods such as lentils, chickpeas, spinach, tofu, pumpkin seeds, wholemeal bread and fortified cereals, is absorbed at a much lower rate, typically 17% or less, depending on what else you eat at the same meal.

For most healthy adults with mild depletion, a diet consistently rich in haem iron sources can help maintain stores. Vegetarians and vegans who eat a varied diet with plenty of legumes, seeds, and vitamin C alongside iron-rich plants can also maintain adequate levels, though it takes more attention to food pairing and the margin for error is smaller. If you eat meat substitutes, the Voedingscentrum advises choosing ones with added iron and vitamin B12: to fit the Schijf van Vijf, a meat substitute needs at least 2.1 mg of iron per 100 g .

Where diet alone tends to fall short is in the context of significant deficiency, heavy menstrual losses, pregnancy, frequent blood donation, or malabsorption. In those situations, food can slow the decline but typically cannot reverse it quickly enough. The gut can only absorb so much iron per day regardless of intake, and raising depleted stores meaningfully usually requires supplemental iron, at least in the short to medium term.

Supplement forms: what the evidence says and what to choose

If you've been told to take iron, or are considering supplementing, the form matters. Here is how to think about the main options and where to start.

Ferrous fumarate (ferrofumaraat) is what Dutch GPs prescribe first. The NHG guideline advises 200 mg twice a week, on days that are not consecutive , rather than a tablet every day. It is inexpensive, well absorbed in people who are iron-deficient, and taking it less often keeps stomach complaints down.

Ferrous sulfate and ferrous gluconate are also ferrous (iron 2+) forms. Ferrous sulfate is the most widely prescribed form internationally, but it is also the form most associated with gastrointestinal side effects: constipation, nausea, and stomach cramps. These side effects lead many people to stop taking it. Ferrous gluconate tends to be gentler on the gut while maintaining reasonably good bioavailability, and has a reasonable evidence base for tolerability.

Ferric forms (iron 3+), such as ferric phosphate or ferric pyrophosphate, need to be converted to the ferrous form in the gut before absorption, which makes them less bioavailable in most circumstances. Some newer formulations use micronized or liposomal delivery to improve this.

Liposomal iron encapsulates iron in a lipid layer that allows it to be absorbed through a different pathway, bypassing some of the gut reactions that cause side effects with traditional supplements. Some randomized trials suggest liposomal iron may perform comparably to ferrous sulfate for raising ferritin, with consistently fewer gastrointestinal complaints, though the evidence base is still developing.

Iron bisglycinate (iron chelate) is a form bound to the amino acid glycine. It has better absorption than ferric forms and is generally well-tolerated, with a systematic review and meta-analysis finding fewer GI adverse events compared with other iron supplements , making it a popular choice in food supplements sold without prescription.

If your GP diagnoses iron deficiency, you will most likely be prescribed ferrous fumarate. If you are choosing a supplement yourself, ferrous fumarate, ferrous gluconate, or iron bisglycinate are reasonable first choices: better tolerated than ferrous sulfate, with good bioavailability, and widely available at the pharmacy or drugstore without prescription. If you've tried ferrous sulfate before and stopped because of stomach problems, any of these three is worth trying instead. If you've tried oral iron repeatedly without raising your ferritin, or can't tolerate it at all, that's the point at which intravenous iron becomes worth discussing with your GP.

Practical points on dosing and routes of administration

Iron absorption is enhanced by vitamin C taken at the same time, and inhibited by calcium, tannins (tea, coffee), and phytates (wholegrains, legumes). Thuisarts.nl advises taking the tablet in the morning before breakfast, with an orange or a kiwi, and leaving coffee, tea and milk for 4 hours before and 2 hours after. Taking iron on an empty stomach increases absorption but also increases the chance of stomach upset. Taking iron every other day rather than daily has evidence supporting 30182-5) better net absorption, because daily dosing triggers a hepcidin response that temporarily reduces absorption the following day. Dutch guidelines already build on this, which is why GPs here prescribe iron two days a week.

Beyond oral supplements, two other routes of administration are used clinically when oral iron isn't working or isn't tolerated.

Intravenous (IV) iron infusion delivers iron directly into the bloodstream, bypassing the gut entirely. It is typically reserved for people with significant anaemia, malabsorption conditions such as inflammatory bowel disease or coeliac disease, or those who have repeatedly failed oral supplementation. In the Netherlands it is given in hospital, usually after your GP refers you to a specialist. IV iron can raise ferritin levels substantially faster than oral routes, often within weeks, and newer formulations such as ferric carboxymaltose can deliver a full therapeutic dose in a single session . It requires a clinical setting and carries a small risk of infusion reactions, though serious adverse events are uncommon with modern preparations.

Intramuscular (IM) iron injection is an older method that is now rarely used. Absorption is unpredictable and the injections can be painful and cause lasting skin discoloration at the injection site. IV iron has largely replaced it in clinical practice.

For most people with confirmed deficiency who don't have a malabsorption condition, oral iron taken correctly and in a well-tolerated form remains the standard starting point. Following the NHG guideline , Dutch GPs check haemoglobin again after about four weeks and continue treatment for two to three months after it has normalised, to refill the stores. IV infusion is an effective escalation option when oral therapy isn't sufficient.

None of this replaces a proper assessment. Supplementing without knowing your actual levels means you may take more than you need. While iron toxicity from food sources isn't a concern, excessive supplementation over time carries real risks. Testing first gives you a baseline, tells you whether deficiency is present, and lets you track whether the intervention is working.

How Ahead measures your iron status

Ahead's Advanced blood test includes a full iron panel, covering ferritin, serum iron, transferrin, and transferrin saturation, interpreted alongside inflammatory markers (hs-CRP, SIRI, SII) so that ferritin can be read in context. It is part of a broader analysis that also covers your blood count, heart, metabolism, liver, kidneys, thyroid and vitamin D. Results are reviewed by Dutch doctors, not just flagged against standard reference ranges. That distinction matters for iron in particular, where the clinical interpretation often diverges from what a lab's automated threshold would flag.

Ahead's services complement your GP rather than replacing them. If deficiency is confirmed, the report gives you and your GP a clear, documented baseline to work from.

Conclusion

Iron deficiency is common, under-detected, and often under-treated, not because it's hard to measure, but because the standard tests don't always measure enough. Haemoglobin alone tells you whether you're anaemic. Ferritin, serum iron, transferrin, and transferrin saturation together tell you where you are on the path before you get there.

If you've been tired in a way that doesn't make sense, or your hair is falling out and your GP hasn't found anything, it's worth asking whether your iron stores have actually been checked, not just your red blood cells.