Blood Tests



1. Hb (Haemoglobin)
•    Low- anaemia (<13 men <11.5 women)
•    High- polycythaemia (>18 men >16 women) - look at PCV to rule out apparent polycythaemia

2. MCV (Mean Cell Volume)
Determines whether the anaemia is microcytic, normocytic or macrocytic.

a) Low MCV (microcytic)
•    Iron deficiency anaemia- usually from blood loss (especially GI  and uterine)
•    Thalassaemia- increased serum iron, increased ferritin and low TIBC

b) Normal MCV (normocytic)
•    Anaemia of chronic disease
•    Aplastic- deficient of other cells types – reticulocytes, WCC
•    Renal failure
•    Hypothyroidism
•    Haemolytic- raised unconjugated bilirubin or spherocytosis

c) High MCV (macrocytic)
Hypersegmented neutrophils or marrow aspirate identifies megaloblasts. Causes:
•    Liver disease
•    Alcoholism or B12/folate deficiency- due to coeliac disease, pernicious anaemia
•    Hypothyroidism

3. RDW (Red cell distribution)
Indicates distribution of red cell sizes- raised if two distinct red cell populations present

4. PLT (Platelets) 150- 400
a) High (thrombocytosis)
•    Primary haematological disease: chronic myeloid leukaemia, myelodysplasia
•    Secondary (reactive) to: infection, inflammation, malignancy, bleeding

b) Low (thrombocytopenia)
Reduced production- viral infections (infectious mononucleosis), drug induced (penicillamine), leukaemia, aplastic anaemia
Increased destruction- autoimmune idiopathic thrombocytopenic purpura, hypersplenism, DIC, after a massive blood transfusion

5. PCV (Packed Cell Volume = Haematocrit)
•    Increased- polycythaemia or plasma loss (dehydration, burns causing apparent polycythaemia)
•    Decreased- blood loss (ECF attempts to compensate + IV fluids given)

6. WBC (White Blood Cells) 4-11
The differential count is more useful

a) Neutrophils
•    Increased (neutrophilia) – bacterial infections, inflammation, necrosis (e.g. post MI), corticosteroids, myoproliferative disorders
•    Decreased (neutropenia) – post radiotherapy or chemotherapy, viral infection, post adverse drug reaction (e.g. clozapine)

b) Lymphocytosis
•    Increased (lymphocytosis)- viral infections, chronic infections, leukaemia and lymphoma
•    Low- TB and HIV

c) Eosinophilia- Increased in allergic reactions and helminth worm infections



Last updated: 15/02/15
Author: Johno Breeze