Full blood count
A full blood count (FBC) is a haematological laboratory investigation measuring:
- haematologic indices - mean cell volume, haematocrit, mean cell haemoglobin,
- platelet count,
- white cell count
In some places a white cell count differential is also included in the test which gives the a breakdown of the various sub-types of white cells, namely neutrophils, monocytes, lymphocyte, basophils and eosinophils.
A blood sample for a FBC is usually collected in a tube containing an anti-coagulant, most commonly potassium-EDTA. EDTA causes anti-coagulation by removing calcium, an essential component in the clotting cascade (EDTA chelates calcium).
From birth to 2 months there is a fall in erythrocyte count and a rapid loss of fetal haemoglobin. Erythrocyte count gradually increases to about 2 years and then stays stable until about 8 years until a rapid increase to about age 15 where values settle to adult values with a sex difference. As shown in the figure, there is a fall in haemoglobin concentration to a minimum about age 6 months and an increase as adolescence sets in, with increasingly marked male and female differences. There is minimum change in haemoglobin in healthy men and women after menstruation ceases. Haemoglobin concentration in capillary (cutaneous) blood is greater than venous blood.
Delaying tying the umbilical cord until after placental expulsion increases a neonate's Hb by about 2.6g/dl. Haemoglobin concentration normally falls in pregnancy but anaemia is important to treat in pregnancy!
Reticulocyte count falls from birth to a low at about 2 weeks, increases to about 4 months then falls through life. There is a sex difference.
The variations with white blood cells in the blood with age are even more complex. At birth there is a high neutrophil count, typically in the range 15 to 45 X 109/l which falls rapidly in first 2 days. Absolute lymphocyte count exceeds the neutrophil count from about 6 weeks to 4 years. Monocyte absolute count steadily decreases with age until the teens. Eosinophils have a day time variation with maximum about midnight and two minima in early morning and late afternoon, and a perhaps not unexpected seasonal fluctuation or with menstrual cycle (maximum at menstruation, minimum at ovulation). Black Africans have lower white cell counts as their leucocytes tend to marginate more than Causacian races.
- ↑ Bain B, Seed M, Godsland I. Normal values for peripheral blood white cell counts in women of four different ethnic origins. Journal of clinical pathology. 1984 Feb; 37(2):188-93.
- ↑ Bain BJ. Ethnic and sex differences in the total and differential white cell count and platelet count. Journal of clinical pathology. 1996 Aug; 49(8):664-6.