Serum haemoglobin measurement is a common laboratory test in hospitalised patients. Laboratory-recorded Hb is a concentration and its value will be modified by both a change in its content, and a change in its diluent (plasma). Thus, a patient’s Hb may not be elevated (i.e. in the ‘normal’ range) despite a sudden loss of intra-vascular volume, as is seen with acute haemorrhage.

Remember to treat the patient, not the laboratory value.

Anaemia is defined as Hb <125 g/L in adults or 110 g/L in children. It is important to take an accurate history, perform a systematic examination, review the mean corpuscular haemoglobin (MCH) and mean corpuscular volume (MCV), and determine the presence of additional cells, such as reticulocytes, to define the cause of anaemia.

Causes of low Haemoglobin

  1. Physiological
    • Pregnancy
  2. Reduced RBC production
    • Hypochromic (↓MCH), microcytic (↓MCV)
      • Iron deficiency, Lead poisoning
      • Thalasemia (not Minor)
      • HbE trait (Malaysian, Vietnamese)
    • Normochromic, normocytic (Check reticulocytes)
      • Hyporegenerative(Decreased reticulocyte count)
        • Primary marrow failure (Myelofibrosis, aplastic anaemia)
        • Secondary marrow failure (AOCD, uraemia, alcohol)
      • Normoregenerative(Elevated reticulocyte count)
        • Acute blood loss or haemolytic anaemia this is not Reduced RBC production
    • Normochromic macrocytic (↑MCV) (Megaloblastic)
      • Folate deficiency
        • Pregnancy, trimethoprim, malabsorption, methotrextae
      • B12 deficiency
        • Pancreatic disease, pregnancy, hypothyroid, liver disease
        • Intrinsic factor deficiency (PA or gastrectomy)
        • Zidovudine, azothioprine


  3. Increased RBC loss (Usually normochromic, normocytic)
      • Genetic
        • Membrane (Spherocytosis)
        • Enzyme defect (G6PD, pyruvate kinase)
        • Haemoglobin (Thalasemia, sickle cell)
      • Acquired
        • Immune(Spherocyte associated)
          • Iso-immune (Newborn, blood transfusion)
          • Autoimmune (Warm, cold, drug)
        • Non-immune(Schistocyte associated)
          • Microangiopathic (DIC, TTP, HUS, PET, HELLP) – Valves, hypersplenism, metastatic Adenocarcinoma
          • Environmental (hyperthermia)
          • Infection (Malaria, septicaemia, mycoplasma)
    • Haemolytic anaemia

Haemolytic anaemias (Lab findings)

  • Anaemia (Usually normochromic normocytic)
  • Increased reticulocytes (Normoregenerative)
  • Abnormal cells present in smear
    • Spherocytes (hereditary, immune mediated (especially warm))
    • Schistocytes (Non-Immune, microangiopathic, micro and macrovasculature trauma)
  • Increased LDH (specific and used to track course of disease)
  • Increased unconjugated bilirubin
  • Increased plasma free Hb
  • Decreased Haptoglobin
    • Acute phase protein
    • Increased in AMI, burns, tissue destruction, severe infection, cancer
    • Decreased in Haemolytic anaemia

Iron Function Tests


  • High: Haemachromatosis, Hepatic disease, iron overload, leukemia, Renaldisease, Hodgkin, chronic HA
  • Low: Chronic iron deficiency
Print Friendly