Full Blood Count
The full blood count is one of the most important common tests the clinicians use. Whilst there are many variables and values that this includes, as a junior doctor, you will mostly be focussing on 3.
Haemoglobin
This is the functional molecule of RBCs, which is composed of 4 polypeptide chains – 2 alpha, 2 beta
Each chain carries a prosthetic haem group which is responsible for binding oxygen
A haem group consists of an iron (Fe2+) ion (charged atom) held in porphyrin rings, which are bound by their nitrogen atoms to the central Fe2+ ion
In adults, the most common hemoglobin type is a tetramer (which contains four subunit proteins) called haemoglobin A, consisting of two α and two β subunits non-covalently bound, each made of 141 and 146 amino acid residues respectively.
Normal concentration
Men 135-175 g/L
Women 115-155 g/L
We are usually concerned by falling concentrations of haemoglobin (anaemia). Anaemia is defined as a low haemoglobin (Hb) concentration, which can be either due to a reduced RBC mass or increased plasma volume (e.g. in pregnancy).
There are many causes of anaemia, which you can read more about in the haematology notes section.
White Cell Count
This is a quantitative measure of the white cells in your bloodstream. It gives you an overall count as well as the number of different types of white blood cell, including neutrophils, lymphocytes etc.
The main reason we look at this count as a junior doctor will be to see if there is an inflammatory/infective process occuring.
Normal concentration
WCC 4.0-11.0 x 10^9/L
Causes of raised WCC
Infection
Steroids
Autoimmune disease
Cancer e.g. lymphoma, leukhaemia
Causes of reduced WCC
Chemotherapy – make sure to watch out for neutropenic sepsis
Bone marrow failure
Immunosuppressive drugs
Viruses e.g. HIV
Bone marrow transplant e.g. whole body irradiation
CRP
The white cell count is often looked at in conjunction with the CRP to look at the levels of inflammation.
It is an acute-phase protein which is made by the liver that increases following interleukin-6 secretion by macrophages and T cells.
Normal values should be < 5, but this can rise to over 100 in an infection. CRP also rises in an inflammatory state, e.g. autoimmune disease, cancer
A raised CRP in conjunction with WCC should prompt the doctor to look for causes of inflammation, which will very often be an infection.
Platelet Count
This is a measure of the number of circulating platelets in the bloodstream. Too few platelets gives a high risk of bleeding whereas too high gives a risk of thrombosis.
Normal Count
150-400 x 10^3/uL
Generally it takes a significant decrease in platelet count to cause visible symptoms. Different procedures have different thresholds regarding the platelet count, but it is possible to do surgeries with a platelet count <100. Similarly patients have be asymptomatic with a platelet count <10.
Causes of raised platelet count
Infection
Inflammation
Hyposplenism
Myeloproliferative disorders – polycythaemia vera, essential thrombocythaemia, chronic myeloid leukhaemia
After surgery
Causes of reduced platelet count
Chemotherapy, antibiotics (e.g. vancomycin)
Heparins
Bone marrow failure
Sepsis
Viruses e.g. HIV, hepatitis C
Pregnancy
Automimmune e.g. ITP, TTP
Disclaimer
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