6- Blood Counts & Films

Question 1

• in what factors can there be a normal change in range in blood results?
• why should you treat the patient, not the result?
• describe points in pathology screening where errors may take place.

Answer 1

• normal changes based on ethnicity, age, sex, co-morbidities
• because blood tests are often reactive of an underlying disorder, interpret in light of clinical context and ask if it fits w the clinical scenario
• specimen mix up, poor technique in specimen collection, pooling of samples, wring delivery method, incorrect clinical details, wrong test performed/ordered, result given to wrong patient.

Question 2

• what is the full blood count & what is it used to test for?
• how is it analysed?
• what is the ‘packed cell volume’? (PCV/Hct)

Answer 2

• automated test, great accuracy, tests for RBCs (incl. Hb, count & shapes+ sizes), platelet count, white cells count
• via spectrophotometry (amount of light absorbed by sample ~ to amount of absorbent inside compound, calibration curve), flow cytometry (counts scatter to give size, more scatter= bigger cell)
• PCV= proportion of blood that is made up of RBCs, centrifuged blood separates blood into plasma(yellow-water proteins, nutrients), buffy/foam coat(WBCs, platelets) and haemocrit (RBCs only) so can visualise. Used to assess anaemia but more often polycythaemia (where haemocrit is increased)

Question 3

For each of the following cell types tested for in the full blood count, describe & give what conditions the assessment screens for:

• Hb
• red cell count (RCC)
• mean cell volume (MCV)
• mean cell Hb (MCH)
• mean cell Hb concentration (MCHC)
• red cell distribution width (RCW)
• reticulocyte count

Answer 3

• Hb=the Hb conc in the blood ie amount of Hb mass/plasma vol, reduced by acute bleed and dehydration, turbidity of plasma (cloudiness) can lead to overestimate.
• red cell count= number of RBCs in given vol of blood, used to assess anaemia and erythrocytosis (increase in RBCs, polycythaemia) eg microcytic anaemias RCC is reduced in iron deficiency anaemia, increased in thalassaemia trait
• mean cell vol= mean size of RBCs, measured using amount of light scattered, most important when screening for anaemias- high ie bigger cells in megaloblastic anaemias, liver disease, alcohol, haemolytic anaemias (bc reticulocytes are bigger). Low ie smaller cells in iron deficiency anaemias, thalassaemia
• mean cell Hb= average measure of amount of Hb in each RBC, used to assess for anaemia, lower in iron deficiency, normal of increased in macrocytic anaemias
• mean cell Hb conc=mean conc of Hb in cells, least useful, increased in spherocytosis, in lab can identify cold agglutinins.
• red cell distribution width=variation in size of RBCs, if lots of variation=anisocytosis, used to assess cause of anaemia, lots of diff sizes in iron def anaemia, normal in thalassaemia trait & after transfusion
• reticulocyte count=measurement of young erythrocytes, use size and RNA content, increased (where there RBCs lost) in haemolytic anaemias, recent blood loss, recovery from bone marrow suppression. Decreased in RBC gain eg haematinic deficiency (not enough nutrients to make RBCs), bone marrow failure

Question 4

• when is a sample flagged as requiring a blood film?
• define= microcytic, macrocytic, hypochromic, hyperchromic
• define:anisocytosis, dimorphism, poikilocytosis, spherocytosis,eliptocytes.

Answer 4

• if there are significant changes outside of the norm or w/in the norm, abnormal cells present
• microcytic=small, macrocytic=big, hypochromic=pale so less Hb, hyperchromic=dense so more Hb
• anisocytosis=variability in size, dimorphism=2 distinction populations of cells, poikilocytosis=abnormally shaped RBCs, spherocytosis=spherical, eliptocytosis=elliptical shaped

Question 5

• name some inclusions found in abnormal RBCs
• outline the expected blood results of someone w iron deficiency anaemia.
• outline the expected blood results of someone w B12 deficiency anaemia.
• why do platelets counts tend to change a lot?

Answer 5

• Howell-Jolly bodies=DNA fragments, Heinz bodies=denatured Hb
• lowered Hb, lower mean cell volume & mean cell Hb and mean cell Hb conc, reticulocyte count low (or normal but shouldn’t be normal bc it means body has enough iron to make RBCs but they’re not being made or don’t last long), anisocytosis, hypochromic
• low Hb, low red cell count, high variation in cell sizes, bigger cells, low reticulocyte count
• bc platelets are very reactive, can clot which would recuse their count.