Anaemia Blood Test: Going Beyond Haemoglobin

Anaemia is one of the most common health conditions worldwide, affecting an estimated 1.6 billion people globally. In the United Kingdom, the picture is particularly striking among certain groups: 23% of pregnant women and 14% of non-pregnant women of reproductive age are anaemic, according to NHS data. Yet despite its prevalence, anaemia is frequently diagnosed late or incompletely, because too many screening approaches rely solely on haemoglobin.

Haemoglobin tells you whether you are anaemic. It does not tell you why. And without knowing the cause, treatment is guesswork.

What Is Anaemia?

Anaemia is defined as a reduction in the oxygen-carrying capacity of the blood, most commonly measured by haemoglobin concentration. The World Health Organisation thresholds are:

• Women (non-pregnant): Below 120 g/L
• Women (pregnant): Below 110 g/L
• Men: Below 130 g/L

Symptoms include persistent tiredness, shortness of breath on exertion, pallor, dizziness, heart palpitations, headaches, and difficulty concentrating. The insidious nature of anaemia is that it often develops gradually, and many people normalise their symptoms for months or years before seeking medical attention.

The Full Blood Count: Your Starting Point

A full blood count (FBC) is the foundation of anaemia investigation. Beyond haemoglobin, the FBC provides several critical indices:

Mean Corpuscular Volume (MCV)

MCV measures the average size of your red blood cells and is arguably the most important clue to the type of anaemia you have:

• Microcytic (MCV below 80 fL): Small red blood cells — think iron deficiency, thalassaemia trait, chronic disease, or lead poisoning
• Normocytic (MCV 80-100 fL): Normal-sized cells — anaemia of chronic disease, early iron deficiency, renal anaemia, or acute blood loss
• Macrocytic (MCV above 100 fL): Large red blood cells — B12 deficiency, folate deficiency, alcohol excess, hypothyroidism, or certain medications

Mean Corpuscular Haemoglobin (MCH) and MCHC

MCH indicates the average amount of haemoglobin per red cell, whilst MCHC reflects the concentration. Low MCH and MCHC (hypochromic) strongly suggest iron deficiency. These values help confirm what the MCV is indicating.

Red Cell Distribution Width (RDW)

RDW measures variation in red cell size. An elevated RDW in the context of microcytic anaemia favours iron deficiency over thalassaemia trait (where cells are uniformly small). It is a genuinely useful discriminator that is often overlooked.

Ferritin: The Iron Stores Test

Ferritin is the storage form of iron in the body. It is the single most sensitive and specific test for iron deficiency. The critical insight that many people miss is this: ferritin can be low even when haemoglobin is normal.

This state — iron depletion without anaemia — is extremely common, particularly in menstruating women, vegetarians, endurance athletes, and frequent blood donors. Symptoms of low ferritin (fatigue, poor concentration, hair thinning, restless legs) can be debilitating even without frank anaemia.

Reference ranges vary between laboratories, but generally:

• Below 15 µg/L: Confirms iron deficiency
• 15-30 µg/L: Probable iron depletion — many clinicians now consider this suboptimal
• 30-100 µg/L: Generally adequate for most people
• Above 100 µg/L: Replete stores (though very high levels warrant investigation for inflammation or haemochromatosis)

One important caveat: ferritin is an acute phase reactant, meaning it rises during infection, inflammation, or liver disease. A person can have iron deficiency masked by a falsely elevated ferritin during illness. If CRP is raised simultaneously, ferritin must be interpreted cautiously — a level below 100 µg/L in the setting of active inflammation may still represent functional iron deficiency.

Iron Studies: The Full Picture

When ferritin alone does not give a clear answer, a full iron panel adds clarity:

• Serum iron: The amount of iron circulating in your blood, bound to transferrin. It fluctuates significantly throughout the day and is affected by recent meals, so fasting samples are preferred.
• Transferrin: The transport protein that carries iron through the bloodstream. Transferrin rises when iron stores are low (the body produces more transporter to try to capture every available iron molecule) and falls in iron overload or chronic inflammation.
• Transferrin saturation (TSAT): Calculated from serum iron and transferrin. TSAT below 16-20% suggests iron-deficient erythropoiesis — your bone marrow does not have enough iron to produce red blood cells efficiently. TSAT above 45% raises concern for iron overload conditions such as hereditary haemochromatosis.
• Total iron-binding capacity (TIBC): Reflects the maximum amount of iron that transferrin can carry. Elevated TIBC indicates iron deficiency; low TIBC suggests chronic disease or iron overload.

Vitamin B12 and Folate

B12 deficiency and folate deficiency both cause macrocytic anaemia — characterised by abnormally large red blood cells (MCV above 100 fL). These two nutrients are essential for DNA synthesis in rapidly dividing cells, including the red blood cell precursors in your bone marrow.

B12 deficiency affects an estimated 6% of adults under 60 and up to 20% of those over 60 in the UK. It can result from dietary insufficiency (particularly in vegans and vegetarians, since B12 is found almost exclusively in animal products), pernicious anaemia (an autoimmune condition that destroys the intrinsic factor needed for B12 absorption), or malabsorption conditions such as coeliac disease or Crohn's disease.

Folate deficiency is less common since the body stores less folate than B12 (reserves last weeks rather than years). Poor dietary intake, coeliac disease, excessive alcohol consumption, and certain medications (particularly methotrexate and anticonvulsants) are the main causes.

Both B12 and folate should be measured together, because supplementing one while the other is deficient can mask the deficiency and allow neurological damage to progress — particularly in the case of B12 deficiency, which can cause irreversible nerve damage if left untreated.

Reticulocyte Count

Reticulocytes are immature red blood cells freshly released from the bone marrow. A reticulocyte count tells you how actively your bone marrow is producing new red cells. In anaemia, the expected response is increased reticulocyte production (reticulocytosis). If the reticulocyte count is inappropriately low despite anaemia, it suggests the bone marrow itself is impaired — whether from nutrient deficiency (iron, B12, folate), chronic disease, or a primary marrow disorder.

Common Patterns to Recognise

Pattern	MCV	Ferritin	B12/Folate	Likely Cause
Low Hb, low MCV, low ferritin	Below 80	Below 15	Normal	Iron deficiency anaemia
Normal Hb, low ferritin	Normal	Below 30	Normal	Iron depletion (pre-anaemia)
Low Hb, high MCV, low B12	Above 100	Normal	Low B12	B12 deficiency anaemia
Low Hb, normal MCV, raised CRP	80-100	Normal/raised	Normal	Anaemia of chronic disease
Low Hb, low MCV, normal ferritin, ethnicity risk	Below 80	Normal	Normal	Thalassaemia trait

How to Test With Lola Health

Our Blood Health 6 test (£89) is purpose-built for anaemia investigation, covering iron, ferritin, B12, folate, and transferrin alongside a full blood count. If you want a more comprehensive metabolic screen that also includes kidney function, liver function, thyroid, and inflammatory markers, the Core Health 45 test (£120) provides all of these alongside your anaemia markers.

All tests use a venous blood sample collected at one of our partner clinics or via our home phlebotomy service. Results are typically available within 48-72 hours, reviewed by our clinical team, and presented with clear commentary explaining what your results mean and what to do next.

When to Retest

If you have been started on iron supplementation, NICE recommends rechecking a full blood count and ferritin after 2-4 weeks to confirm a haemoglobin response, and again at 2-3 months to verify that stores are being replenished. For B12 injections, a follow-up FBC at 8-10 weeks is standard to confirm the macrocytosis is resolving.

If you have unexplained symptoms — persistent fatigue, breathlessness, hair loss, or difficulty concentrating — a comprehensive anaemia panel is one of the most productive first steps you can take. Catching iron depletion before it becomes frank anaemia means simpler treatment, faster recovery, and the reassurance of knowing exactly what is driving your symptoms.