deciding what is normal and interpreting blood counts

Question 1

reference/ normal range

Answer 1

range derived from healthy population, so 95% of population (excluding 2.5% at either end)

Question 2

factors affecting normal

Answer 2

age, gender, ethnic origin, physiological status, altitude (higher altitudes have higher normal ranges), nutritional status, smoking/alcohol

Question 3

reference vs normal range

Answer 3

reference range very strict- from a strictly define population eg no smoking normal range more ambiguous

Question 4

how to determine reference range

Answer 4

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

Question 5

caveats of reference range

Answer 5

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

Question 6

what’s in a full blood count

Answer 6

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

Question 7

how to do WBC, RBC and platelet count

Answer 7

either counting via microscope OR large instruments to emit electrical field/light source, which is disturbed when cells pass

Question 8

how to measure Hb

Answer 8

spectrometer, converting haemoglobin to stable form and measuring light absorption

Question 9

how to measure haematocrit/ PCV (packed cell volume)

Answer 9

centrifuge blood sample, measure right of RBC layer, and express as %

Question 10

calculate MCV

Answer 10

divide total volume of RBC (ie PCV) by number of RBC

Question 11

calculate MCH

Answer 11

divide amount of haemoglobin in given volume (Hb) by number of RBC

Question 12

calculate mean cell haemoglobin conc.

Answer 12

divide amount of haemoglobin (Hb) by proportion of sample that is RBC (HCT)

Question 13

MCH vs MCHC DIAGRAM

Answer 13

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

Question 14

measuring MCHC DIAGRAM

Answer 14

light scattering used to create scatter plots, with lines representing standard deviations top has bottom MCHC= potentially thalassaemia bottom is hereditary spherocytosis

Question 15

interpreting a blood count

Answer 15

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

Question 16

polycythaemia definition and what occurs in blood count

Answer 16

increased RBC in circulation- will have high RBC, Hb and HCT

Question 17

causes of polycythaemia

Answer 17

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

Question 18

what is pseudopolycythaemia

Answer 18

reduced plasma volume, so MCHC and HCT increases, but RBC stays same

Question 19

evaluating polycythaemia

Answer 19

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

Question 20

polycythaemia vera- cause and effect, and feature

Answer 20

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

Question 21

treating polycythaemia

Answer 21

if high viscosity, blood can be removed to think it if disease of bone marrow (polycythaemia vera), drugs can reduce erythropoeisis in bone marrow