deciding what is normal and interpreting blood counts Flashcards
reference/ normal range
range derived from healthy population, so 95% of population (excluding 2.5% at either end)
factors affecting normal
age, gender, ethnic origin, physiological status, altitude (higher altitudes have higher normal ranges), nutritional status, smoking/alcohol
reference vs normal range
reference range very strict- from a strictly define population eg no smoking normal range more ambiguous
how to determine reference range
data measured same instruments and techniques, and analysed using a statistical technique normally (gaussian) distributed data- mean and SD calculated, and mean+- 2 SD’s is the 95% range
caveats of reference range
not all results outside range is normal, but not all results within range is normal- for an individual patient, a certain event like a haemmorhage may decrease blood count and still be normal in range, but not normal for him just because you are in range doesn’t mean you are healthy eg blood lipids
what’s in a full blood count
WBC (no. in given volume) RBC Hb- haemoglobin concentration Hct- haematocrit MCV- mean cell volume MCH- mean cell haemoglobin MCHC- mean cell haemoglobin conc (g/l) platelet count- number in a given volume
how to do WBC, RBC and platelet count
either counting via microscope OR large instruments to emit electrical field/light source, which is disturbed when cells pass
how to measure Hb
spectrometer, converting haemoglobin to stable form and measuring light absorption
how to measure haematocrit/ PCV (packed cell volume)
centrifuge blood sample, measure right of RBC layer, and express as %
calculate MCV
divide total volume of RBC (ie PCV) by number of RBC
calculate MCH
divide amount of haemoglobin in given volume (Hb) by number of RBC
calculate mean cell haemoglobin conc.
divide amount of haemoglobin (Hb) by proportion of sample that is RBC (HCT)
MCH vs MCHC DIAGRAM
density of dots is same, but fewer dots- central pallor is same thus MCH is amount of haemolobin a RBC, MCHC is concentration in a RBC MCHC relates to shape of cell- spherocytes and sickle cells have a higher MCHC
measuring MCHC DIAGRAM
light scattering used to create scatter plots, with lines representing standard deviations top has bottom MCHC= potentially thalassaemia bottom is hereditary spherocytosis
interpreting a blood count
look at WBC- If high, probs because there is high neutrophils (most abundant WBC)- look at absolute count rather than % look at Hb look at MCV look at platelet count may then need to look at blood film- if patient has anaemia, looking at film for sickles confirms sickle cell anaemia
polycythaemia definition and what occurs in blood count
increased RBC in circulation- will have high RBC, Hb and HCT
causes of polycythaemia
blood doping (athletes taking blood) or overtransfunsion appropriate (eg due to high altitude) increase in erythropoetin- hypoxia may cause clubbing of fingers (slightly blue), known as cyanosis inappropriate increase in erythropoetin eg renal tumour polycythaemia vera
what is pseudopolycythaemia
reduced plasma volume, so MCHC and HCT increases, but RBC stays same
evaluating polycythaemia
start with clinical history (splenomegaly means less RBC break down, tumour suggests kidney producing too much erythropoeitin) then compare to an APPROPRIATE normal range (altitude, children and women have lower Hb, RBC and HCT) might be pseudo eg due to dehydration
polycythaemia vera- cause and effect, and feature
mutation in haematopoetic stem cell in bone marrow which increases erythropoeisis, INDEPENDENT of erythropoetin high Hb can lead to high viscosity of blood, which can block arteries often has splenomegaly
treating polycythaemia
if high viscosity, blood can be removed to think it if disease of bone marrow (polycythaemia vera), drugs can reduce erythropoeisis in bone marrow
