Ferritin & Iron Deficiency: What Your Blood Values Reveal

TL;DR: Ferritin is the best early marker for iron deficiency — long before hemoglobin drops. Around 30 % of women of reproductive age have values below 30 ng/ml, many without knowing it. The lab reference range starts at 15 ng/ml, but you only become symptom-free around 60 to 120 ng/ml. Measure ferritin plus transferrin saturation plus hsCRP — only the full panel reveals true deficiency.

This article does not replace medical advice — if you suspect severe iron deficiency, always consult a doctor.

Why ferritin is the most important marker — not hemoglobin

Most general practitioners only measure hemoglobin when patients report fatigue. That is a problem. Hemoglobin stays normal as long as your body can raid the iron stores — and that can go on for months or years. Only when the stores are completely empty does Hb start to drop. By then you already have a fully developed anemia and have felt miserable for months.

Ferritin, by contrast, is the iron store itself. It shows how much reserve your body has right now. If your ferritin sits at 20 ng/ml, your stores are almost empty — even if your hemoglobin is still in the normal range at 13.2 g/dl. This gap between “empty stores” and “anemia” is exactly the window where you can act. For a full overview of all the important blood values, read the cornerstone guide on understanding blood values.

The numbers from European studies are clear: Around 30 % of women of reproductive age have ferritin below 30 ng/ml. In vegan and vegetarian groups this rises above 40 %. In female endurance athletes, 50 to 60 % are below the threshold. This is not a fringe phenomenon — it is a mass deficit.

The 3 stages of iron deficiency

Iron deficiency is not a switch. It is a slow descent in three clearly defined stages — and you can act on every stage.

Stage 1: Latent iron deficiency. Ferritin drops below 30 ng/ml, hemoglobin and all other blood values are still normal. You feel the first symptoms: fatigue despite sleep, concentration issues, sometimes hair loss. The doctor finds “nothing” and sends you home. This is the most common stage — and the most dangerous, because it gets missed.

Stage 2: Functional iron deficiency. The stores are empty (ferritin below 15 ng/ml), transferrin saturation drops below 20 %, but hemoglobin is still just above the line. Symptoms become more pronounced: shortness of breath on exertion, racing heart climbing stairs, cold hands and feet. Red blood cell production is already impaired.

Stage 3: Manifest iron deficiency anemia. Hemoglobin drops below 12 g/dl (women) or 13 g/dl (men), MCV falls below 80 fl (microcytic anemia). Now the problem is clearly visible. You are pale, exhausted, and need urgent substitution — ideally with medical supervision.

The key message: Do not wait until stage 3. If your ferritin is below 30 ng/ml, act now — regardless of hemoglobin.

Ferritin reference ranges: Normal vs. optimal

The lab reference range is statistical, not biological. It shows where 95 % of the population sit — including the 30 % with deficiency. “Normal” here does not mean “healthy”. Optimal values are based on studies looking at symptom freedom and performance.

Group	Lab reference	Optimal	Athlete target
Women (premenopausal)	15–150 ng/ml	60–120 ng/ml	above 100 ng/ml
Women (postmenopausal)	30–200 ng/ml	70–150 ng/ml	above 100 ng/ml
Men	30–400 ng/ml	80–160 ng/ml	above 120 ng/ml
Pregnant (2nd/3rd trimester)	15–150 ng/ml	50–100 ng/ml	—

A concrete example: Your colleague sits at 28 ng/ml and her doctor says the value “is still in the green zone”. Biologically, her stores are 80 % empty. Only at 80 to 100 ng/ml would she truly feel energetic. The reference is the alarm threshold, not the target. For full preparation before your measurement, read the biomarker baseline checklist.

The 8 most common symptoms of iron deficiency

The symptoms are unspecific — that makes self-diagnosis hard. But certain patterns show up often, especially when several occur together. If three or more apply to you, get your ferritin measured.

• Persistent fatigue despite 7 to 9 hours of sleep — the classic
• Brain fog and concentration problems, especially in the afternoon
• Cold hands and feet even at moderate temperatures
• Hair loss, often diffuse across the whole scalp, 50 to 150 extra hairs per day
• Brittle nails with longitudinal ridges or spoon shape (koilonychia)
• Burning tongue or smooth, reddened tongue (glossitis)
• Restless legs, especially in bed at night, urge to move the legs
• Shortness of breath on exertion, racing heart on stairs or short sprints

A concrete example: Your friend has been complaining for 6 months about fatigue, hair loss, and concentration problems. Her doctor measures hemoglobin (13.8 g/dl — “fine”) and sends her home. On her own initiative, she has ferritin measured: 18 ng/ml. After 3 months of bisglycinate supplementation she sits at 45 ng/ml and the fatigue is gone. The only difference: the right measurement.

The full iron panel: Not just ferritin

Ferritin alone is not enough. A complete iron panel costs 60 to 100 euros as a self-pay service at most labs and gives you all the information you need. Here are the six markers that belong together:

Marker	What it shows	Reference range	Optimal
Ferritin	Storage iron (reserve)	15–150 (F) / 30–400 ng/ml (M)	60–120 / 80–160
Transferrin saturation	Currently transported iron	16–45 %	25–40 %
Serum iron	Snapshot, fluctuates heavily	60–170 µg/dl	70–130
hsCRP	Inflammation marker, distorts ferritin	below 3 mg/l	below 1
Hemoglobin (Hb)	Oxygen transport	12–16 (F) / 14–18 g/dl (M)	13–15 / 14–16
MCV	Size of red blood cells	80–96 fl	85–92

The hsCRP value is critical: Ferritin is an acute-phase protein. During inflammation (CRP above 5 mg/l), ferritin rises artificially and hides a real deficiency. In that case, transferrin saturation is the more reliable marker. If it is below 20 %, you have iron deficiency — no matter what ferritin says.

Serum iron alone is unsuitable — it fluctuates by up to 40 % throughout the day. High in the morning, low in the evening. A single measurement without ferritin and transferrin saturation is noise, not signal.

Causes: Why your ferritin is low

Iron deficiency rarely has a single cause. Usually several factors overlap. You can quickly narrow down the common seven causes if you look at your life honestly.

Menstruation. The main cause in premenopausal women. You lose 20 to 30 mg of iron per cycle, up to 50 mg with heavy bleeding. That adds up to 240 to 600 mg per year — more than you can absorb from food. Copper IUDs double the loss, hormonal IUDs reduce it.

Vegetarian and vegan diets. Plant-based non-heme iron is only absorbed at 5 to 10 % (versus 15 to 35 % for heme iron from meat). Vegetarians need about 1.8 times more dietary iron to reach the same status. Without vitamin C at every iron-rich meal, that is hard to achieve.

Intense sport. Runners lose iron through foot strike hemolysis (red blood cells burst with each impact), through sweat, and through microscopic GI bleeding. On top of that, the requirement rises by 30 to 70 %. This explains why 50 to 60 % of female endurance athletes have ferritin below 30 ng/ml.

Chronic inflammation. Here iron is not lost — it is hidden. The body stores it away in cells to isolate bacteria. The result: high ferritin, low transferrin saturation — a functional deficiency despite full stores.

Celiac disease and GI problems. Iron is absorbed in the duodenum. Celiac disease, chronic gastritis (especially with Helicobacter), Crohn’s disease, and proton pump inhibitors reduce absorption by 50 to 80 %. For unexplained iron deficiency, always test for celiac disease.

Pregnancy. Iron requirement rises to 27 to 30 mg per day (normal is 15). Without targeted supplementation, 30 to 40 % of pregnant women develop a deficiency in the 2nd and 3rd trimester.

Silent GI bleeding. Unexplained iron deficiency in men over 40 or postmenopausal women must be investigated gastroenterologically — ulcers, diverticula, or colon cancer can be the cause.

Supplementation: When, how much, which form

Iron is one of the few supplements where form and timing make the difference between effect and waste. Here are the four basic rules for effective supplementation. If you are generally unsure how to start with supplements, read the supplement beginners guide.

The right form. Bisglycinate (iron chelate) is the best choice for most — absorption 25 to 35 %, barely any side effects. Iron fumarate sits around 20 %, is cheaper, but causes stomach issues more often. Iron sulfate (the classic pharmacy option) has similar absorption rates but triggers nausea, constipation, and cramps in 30 to 50 % of users. Heme iron preparations (from blood) are new on the market, expensive, and only useful for severe intolerance.

The right dose. For refilling, 20 to 40 mg of elemental iron per dose is enough. More does not help — above 40 mg, hepcidin blocks absorption in the gut for 24 to 48 hours. High doses like 100 mg are inefficient and stress the stomach.

The right timing. Take on an empty stomach, at least 1 hour before or 2 hours after coffee, tea, dairy, and whole grains. Combine with 100 to 200 mg of vitamin C — this doubles absorption. No calcium, magnesium, or zinc at the same time (they compete for the same transporter).

Every other day instead of daily. New studies (2020 and later) show that iron every other day is absorbed better than daily doses. The reason is hepcidin, a hormone that blocks absorption for 24 to 48 hours after each iron dose. The break allows the gut to fully absorb again. Result: 20 to 40 % more store buildup with half the dose. If you want to add iron to your stack, the supplement stack iteration guide shows you how to measure the effect.

When an iron infusion makes sense

Oral supplements are the first choice for most — cheap, safe, easy to control. But there are clear cases where an infusion is the better option. Discuss it with your doctor if at least one of these three points applies.

Ferritin below 20 ng/ml with clear symptoms. Here you need fast refilling — oral supplements take 4 to 6 months, an infusion only 2 to 4 weeks. If severe fatigue is limiting your ability to work, the faster route is worth it.

Intolerance to oral preparations. About 20 to 30 % of people cannot tolerate iron pills — nausea, constipation, cramps even with bisglycinate. If you still have symptoms after 4 weeks, oral substitution is not an option.

Special cases. Pregnancy with acute deficiency, preparation for surgery, inflammatory bowel disease with impaired absorption, dialysis patients. In these scenarios, infusion is often standard.

Modern preparations (Ferinject, Monofer, Venofer) deliver 500 to 1000 mg of iron in a single session. Cost is 150 to 300 euros per infusion. Statutory insurance covers it with a clear medical indication. Side effects are rare but possible — phosphate drop, skin discoloration at the injection site.

Tracking: How often to test

Iron deficiency is not a one-time problem. Anyone who has been affected — especially women, athletes, and vegetarians — needs long-term tracking. Here is the rhythm that works in practice. For methodology details, read the guide on long-term biomarker tracking.

Baseline. Before any intervention, measure ferritin, transferrin saturation, hemoglobin, MCV, and hsCRP. Without these starting values, you cannot tell later whether your supplementation works or just creates noise.

Check after 8 to 12 weeks. That is how long it takes for an intervention effect to show up in ferritin. Measuring earlier is a waste of money, later you miss adjustment opportunities.

Annual check. Even after successful refilling, stay in tracking mode. Once a year, measure ferritin as a standard — for women ideally in the early follicular phase (days 2 to 5), because values fluctuate by up to 30 % across the cycle.

Define a target. Set a concrete target value, for example 80 ng/ml. Without a target you optimize into the void. In Lab2go you enter the target as a benchmark and see at a glance how close your current value is. For other deficiencies that cause similar symptoms, read the vitamin D deficiency guide — often it is not only one value in the basement.

Document context factors. For every measurement, note cycle day, last intense training session, current supplement dose and pauses, infections in the past 2 weeks. Without context, a value is uninterpretable 6 months later.

Conclusion: Measure ferritin early, not late

Iron deficiency is not an exotic problem — it affects 30 % of women of reproductive age, 50 to 60 % of female endurance athletes, and many vegetarians. The danger is not the anemia at the end, but the months to years before it, when you slowly feel worse and nobody finds the cause.

Measure ferritin. Measure it once a year if you are healthy, every 3 to 6 months if you belong to a risk group. Pay attention to the optimal range, not the lab reference. Document context. Act already at values below 30 ng/ml, not only at anemia.

Start today: Order a full iron panel (ferritin, transferrin saturation, hsCRP, blood count), prepare with the baseline checklist, and document everything digitally. For the practical side, check out the features of Lab2go or compare plans and pricing. Your body will show you the difference after 8 weeks — in energy, focus, and training performance.

This article does not replace medical advice. If ferritin is below 15 ng/ml, if symptoms are pronounced, or if the cause of the deficiency is unclear, always consult a doctor. Especially in men over 40 and postmenopausal women, a gastroenterological workup must happen before you start supplementation.