Anaemia in Primary Care: From Blood Count to Cause
Published Oct 12, 2026 · Updated Oct 13, 2026
Anaemia (anemia in North American spelling) is a finding, not a diagnosis. A low haemoglobin tells you something is wrong; the work is finding out what, and how fast you need to act. This guide follows three steps, with the slides from our TopMedCast episode on anaemia: check whether the patient is stable, read the whole blood count, then find and treat the cause. Anemia is one of the CFPC’s priority topics for the family medicine certification exam, and the same traps come up in other licensing exams.
Step 1: is the patient stable?
Before you look at the numbers, look at the patient.
Unstable: active bleeding (black stools or vomiting blood), chest pain or ischaemia, breathlessness at rest, fainting or a rapid decline, poor perfusion or heart failure. These patients need emergency assessment. A reassuring haemoglobin does not exclude major early blood loss, because the count can take time to fall.
Stable: carry on with the workup. Stable iron deficiency anaemia needs iron and a cause, not a transfusion. For stable adults in hospital, transfusion is usually considered below a haemoglobin of 70 g/L, as a guide for the individual patient rather than an automatic rule.
Step 2: read the whole blood count
Don’t stop at the haemoglobin. The MCV sorts the anaemia into a category, the RDW shows how much red cell size varies, and the white cells and platelets point to marrow disease, inflammation or other urgent problems. Compare every result with the patient’s previous counts: a change matters as much as a single value.
Microcytic (MCV under 80 fL): iron deficiency, thalassaemia trait, inflammation.
Normocytic (80 to 100 fL): early iron deficiency, kidney disease, inflammation, blood loss, haemolysis.
Macrocytic (over 100 fL): vitamin B12 or folate deficiency, alcohol or liver disease, hypothyroidism, medicines, marrow disorders.
These categories guide the tests; they don’t make the diagnosis. Mixed deficiencies, such as iron and B12 together, can give a normal MCV.
The reticulocyte count
When the cause is unclear, check an absolute reticulocyte count and read it against how severe the anaemia is and how long it has been there. A high count means the marrow is working but cells are being lost: think of bleeding or haemolysis. A low or normal count means production is impaired: a deficiency, marrow failure or a lack of erythropoietin.
Iron deficiency: the most common cause
Ferritin is the key test. In a well adult, a ferritin under 30 µg/L supports iron deficiency. Iron deficiency can appear before the haemoglobin falls, and a normal MCV does not exclude it.
Take a 36-year-old woman with fatigue and heavy, prolonged periods: Hb 96 g/L, MCV 73 fL, ferritin 8 µg/L. Replace the iron and treat the cause, but don’t assume the periods explain everything. Ask about diet, blood donation, GI symptoms and malabsorption, and consider whether a bleeding disorder needs investigating.
The ferritin trap
Ferritin rises with inflammation. In chronic inflammatory disease, kidney disease or active infection, a normal or even high ferritin can hide severe iron deficiency. When that is possible, check the transferrin saturation to see how much iron is actually available.
Microcytosis is not always iron deficiency
Long-standing, marked microcytosis with mild anaemia and normal iron stores suggests thalassaemia trait. Iron deficiency anaemia has low ferritin and a low red cell count; thalassaemia trait has normal iron stores and a preserved red cell count. Ask about family history and ancestry and arrange haemoglobinopathy testing. Alpha-thalassaemia trait may need specialist advice to confirm.
Avoid long courses of empirical iron without evidence of iron deficiency.
Unexplained iron deficiency in older adults
A 68-year-old man has new fatigue and no visible bleeding: Hb 101 g/L, MCV 75 fL, ferritin 10 µg/L. His FIT is negative.
Unexplained iron deficiency anaemia in men and postmenopausal women needs urgent gastrointestinal assessment with upper and lower endoscopy. Test for coeliac disease and look for urinary blood loss too.
The FIT trap: a negative faecal immunochemical test does not exclude a GI cause and shouldn’t stop an indicated referral. Here the test is part of a diagnostic workup, not routine colorectal screening, and the absence of weight loss or a change in bowel habit doesn’t remove the need to investigate.
Iron replacement is a process
Start oral iron: ferrous sulphate, fumarate or gluconate. Check the dose of elemental iron, not the tablet weight. Once-daily or every-other-day dosing is better tolerated. If there are side effects such as constipation or nausea, manage them before increasing the dose.
Recheck in 2 to 4 weeks: a meaningful rise in haemoglobin confirms the response.
Refill the stores: don’t stop when the haemoglobin is normal. Continue for about three more months so the stores fill up.
Intravenous iron is for patients who can’t tolerate oral iron, who are unlikely to absorb it, or whose stores don’t improve. It refills the stores, but it doesn’t give the immediate oxygen-carrying support of a transfusion.
Macrocytosis and the nerves
A 72-year-old man on metformin has fatigue, numb feet and poor balance: Hb 104 g/L, MCV 112 fL and a low vitamin B12.
B12 deficiency can damage the nerves even without anaemia, so don’t delay treatment while you wait for every test. Oral cyanocobalamin 1,000 to 2,000 mcg a day works for many patients; severe neurological disease favours starting with intramuscular treatment.
The folate trap: don’t give folic acid alone when B12 deficiency is possible. It can improve the blood count while the nerve damage carries on.
Normocytic anaemia: look beyond nutrition
A normal MCV does not mean a normal workup. Review kidney function, inflammatory disease, medicines and hidden bleeding, and add ferritin, B12, thyroid or liver tests based on the history. Chronic kidney disease reduces erythropoietin production, but never put all of the anaemia down to kidney disease without first ruling out treatable causes.
Recognise haemolysis early
A falling haemoglobin with jaundice or dark urine and a high reticulocyte count suggests haemolysis. Request a blood film, bilirubin, LDH, haptoglobin and a direct antiglobulin test.
Emergency: anaemia with fragmented red cells, low platelets, kidney injury or neurological symptoms suggests a thrombotic microangiopathy, which needs emergency specialist care. Don’t manage this pattern with iron and a wait-and-see plan.
When to refer
Immediately: haemodynamic instability or a suspected thrombotic microangiopathy.
Discuss urgently with haematology: pancytopenia or several low cell lines, a worrying blood film, or a rapidly worsening anaemia.
Routine, but don’t skip it: unexplained persistent anaemia, a poor response to the right treatment, suspected marrow disease, or anaemia in chronic kidney disease that is out of proportion to kidney function (nephrology, for erythropoiesis-stimulating agents).
Urgency depends on the whole clinical picture, not one laboratory value.
Six things not to do
Don’t stop at the haemoglobin. Read the whole count and compare it with earlier results.
Don’t let a negative FIT cancel the GI investigation of unexplained iron deficiency.
Don’t give folic acid alone when B12 deficiency is possible.
Don’t keep giving iron without evidence of iron deficiency.
Don’t stop iron as soon as the haemoglobin is normal.
Don’t treat fragmented red cells and low platelets with iron and waiting.
Listen to the case, then practise
Hear the full discussion in the TopMedCast episode Mastering Anaemia in Primary Care. Then test yourself with exam-style questions in the CCFP SAMP question bank or the MCCQE Part I question bank.
Study takeaway: Check stability first, read the whole blood count, treat iron deficiency and find its cause even when the FIT is negative, never give folic acid alone when B12 may be low, and refer haemolysis with low platelets as an emergency.
Sources
- American Family Physician — Iron Deficiency Anemia: Evaluation and Management (Short and Domagalski)
- British Society of Gastroenterology — Guidelines for the management of iron deficiency anaemia in adults (Snook et al., Gut 2021)
- CFPC — Assessment Objectives for Certification in Family Medicine (priority topics)