Deciding what is normal and interpreting blood counts Flashcards
What is the difference between a reference range and a normal range?
Reference Range = derived from a carefully defined reference population e
Normal Range = much vaguer
How is a reference range determined?
Samples are collected from healthy volunteers with defined characteristics.
The data is analysed by appropriate techniques and instrument.
If the data follows a normal (Gausian) distribution, you can determine what is normal by taking the mean and taking 2 standard deviations on either side. Between the 2 SDs on either side, you will have 95% of the data.
What unit is MCV measured in?
Femtolitres, fL (10^-15L)
What unit is MCH measured in?
Picograms, pg (10^-12g)
How are these parameters measured now?
counted in large automated instruments, by enumerating electronic impulses generated when cells flow between a light source and a sensor or when cells flow through an electrical field
units of WBC
white blood cell count in a given volume of blood (× 10^9/l)
RBC units
RBC – red blood cell count in a given volume of blood (× 10^12/l)
Hb units
g/L
PCV units / Hct units
PCV=Hct same thing.
L/L (litres of RBC per litres of blood)
MCHC units
g/L
platelet units
(× 10^9/l) , same as WBC
what parameter does staining correlate with
MCHC (concentration of Hb per RBC)
What is polycythaemia
abnormal increased rbc
hb, rbc and hct/pcv are all increased
types of polycythaemia and causes
- Polycthaemia– reduced plasma volume
- -dehydrated - True polycythaemia - increased RBC volume
Causes of increase in total volume of red cells in the circulation leading to true polycythaemia
INAPPROPRIATE– No physiological need
- Blood doping/ overtransfusion/ erythropoietin administered inappropriately to haematogically normal subjects–
2.Normal response due to increased EPO, eg hypoxia will cause a physiological increase in EPO APPROPRIATE - inappropriate EPO eg EPO from a kidney tumour
- –independent of eryhropoitin
Intrinsic problem with the bone marrow leading to inappropriately increased ERYTHROPOIESIS NOT EPO in blood. this is called Polycythaemia vera/ primary polycythaemia. ie a problem independent of EPO stimulus
When during the human development is RBC, Hct and Hb the highest?
Neonates (first 28 days after birth) have higher RBC, Hct and Hb than other times of life
Men vs Women, Children vs Adults, who has higher RBC Hct and Hb
Men>women
Adults>children (not neonates)
define Myeloproliferative Neoplasms
When body produces too much of the myeloid lineage cells, including WBC, RBC and platelets.
Name a consequence/complications of polycythaemia
Thick blood/hyperviscosity
=> vascular obstruction
Treatment of polycythaemia
- If there is no physiological need for a high haemoglobin, or if hyperviscosity is extreme, blood can be removed to thin the blood
- If there is intrinsic bone marrow disease (polycythaemia vera) drugs can be used to reduce bone marrow production of red cells
How did Hb used to be measured
Now?
Spectrometer- haemoglobin converted to stable form and measuring light absorption at specific wave length
Same principles, automated instrument
++++How did PVC /hct used to be measured
Centrifuging blood sample
How was Mean cell volume initally calculated
how is it determined now
Dividing total volume of rbc in a sample by no of rbc
Now determined indirectly by light scattering or interruption of an electrical field
Mean cell haemoglobin
Amount of haemoglobin in a given volume of blood divided by the number of red cells in the same volume i.e Hb divided by the RBC
may have same mchc but smaller
MCHC– mean cell haemoglobin concentration
Amount of haemoglobin in a given volume of blood divided by the proportion of the sample represented by the rbc– ie Hb divided by Hct
Correlates with hypochromia/hyperchromia
Removal of blood
Venesection
