Full blood count Flashcards
abnormal results
- Outside the normal range
normal range only includes
- 95% of healthy population
- 2.5% normal values above the range
- 2.5% normal values below the range
results just outside the range may be
normal for that person
Significant fall in value
e.g. 160g/L to 115g/l (both in normal ranges- but still worrying)
nromal rnage changes with
- Age
- Sex
- Ethnicity
- Co-morbidities
If you receive an a result you are not expecting….
repeat test and consider contacting haematologist
interpret abnormal haematology results in light of
clnical context and previous FBC
e.g. to spot acute/chronic change
sources of error
- speciment collection error
- delivery of speicimens to laboratory
- specimen analysis and result reporting
- responsive action
1) Specimen collection error
- Specimen mixed up
- Wrong blood in tube
- Wrong bottle
- Pooling samples
- Adding blood from another tube to fill one up to the line
- Poor technique- may activate (haemolytic) sample
2) Delivery of specimens to laboratory
- Specimen delayed/not delivered
- Wrong delivery method
- Some need to be sent in the dark, on ice, body temp
3) Specimen analysis and result reporting
- Specimen mix up
- Incorrect clinical details
- Wrong test requested/performed
- Inherent test variability
- Technical error
4) Responsive action
- Results not reviewed
- Reflex tests not carried out
- Right result applied to wrong patient
how is the full blood count carried out
Measured using an automated test with a very high level of accuracy that uses an analysing machine that can process thousands of samples every day.
essential parameters of the FBC
-
Red blood cells
- Indices
- RCC
- haemoglobin
- Platelet count
-
White blood cells
- Count
- Full differential
FBC ANALYSER TECHNIQUE
uses Flow cytometry
- hydrodynamic focusing
- single file line of cells
- pass through light beam
- impedance counting
forward scatter=
size
the more scatter= the bigger the cell
Spectrophotometry
*
- Amount of light absorbed by the sample proportional to amount of absorbent compound within it e.g. haemoglobin
- Hypotonic solution to lyse cells
- Use light of appropriate wavelengths
- Use calibration curve to determine sample conc
Flow cytometry differential
- Forward scatter= size
-
Side scatter
-
Mono/polymorphonuclear
- A type of immune cell that has granules (small particles ) with enzymes that are released during infections, allergic reactions, and asthma
-
Intracellular complexity
- Granules
- Myeloperoxidase activity
-
Mono/polymorphonuclear
what are WBC
also known as leukocytes, WBC are cells of the immune system that are responsible for protecting the body againsdt infections or foreign bodies
how are WBCs counted
RBC in a sample of blood are lysed and the majority of remaining cells are WBC.
These are counted automatically as they interrupt a beam of light/ elecrcial current whilst going through a narrow tube in a straight line
what causes an increase in WBC
infection, smoking, leucocytosis, immune system disorders
what causes a decrease in WBC
damaged bone marrow, antibiotics, chemothrrapy drugs
Red blood cells contain
haemoglobin, which gives blood its red colour. The primary role is to transport oxygen and carbon dioxide to and from tissue
how are RBCs measured
measured in the same way as WBC Clight beam) but withou the lysis step.
In comparision to BRC there are very few WBC so it does not affect the RBC count signif
what causes an increase in RBC
congenital causes, hypoxia, polycythaemia vera
what causes an decrease in RBC
anaemia, internal/external bleeding, erythropoietin deficiency
what is haematocrit (HCT)
fraction of the whole blood volume that consists of RBC
how is haemocrit counted
multiply the mean cell volume by the number of RBC per litre
what causes abnormal haemocrit
similar reasons to high/low RBC values
what is haemoglobin concnetreation
the amount of haemoglobin the blood (g/L)
how is haemoglobin conc measured
after red cells have been lysed froma. blood sample, the Hb is converted to a stable form and measured by a colorimeter
what causes an abnormal increase in Hb
living at high altitudes, lung dysfunction (smoking, COPD)
what causes an abnormal decrease in Hb
lack of dietary iron, vitamin B2 or folate ,bleeding , anaemia
what is mean cell volume (MCV)
the average volume of red cells
How is MCV counted
use a beam of light or an electric current, and assess the amount of either that is blocke dby the red cells
what causes an abnormal MCV
macrocytic anaemia >100 fl
microcytic anaemia <80 fl
mean cell haemoglobin (MCH)
a erage amount of hb in an individual RBC
how is mean cell haemoglobin (MCH) counted
divide Hb conc by the number of red cells in a given volume of blood
what causes an abnormal increase in mean cell haemoglobin (MCH)
macrocytic anaemia, insufficient vitamin B12 or folate
what causes an abnormal decrease in mean cell haemoglobin (MCH)
microcytic anaemia, low iron levels
platelets
a fragment of a megakaryocyte invovled in clottign
how are platelets counted
measured the same way as red or white cells.
Platelets produce a much smaller signal (due to their smaller size) so can be easily distinguished
what causes an increase in platelets
thrombocytosis, bone marrow disorders
what causes an decrease in platelets
increased platelt destruction (ITP)
reticulocytes
immature red blood celsl
how are reticulocytes counted
stains and dyes are used which bind to rRNA (not present in mature cells)
what causes an abnormal increase in reticulocytes
high altitudes, hameolytic anaemia, bleeding
what causes a decrease in reticulocytess
aplastic anaemia and bone marrow failure
what are differential white blood cells
analyses te numebr of didfferent white cells in a blood sample
- neutrophils
- lymphocytes
- monocytes
- eosinophils
- basophils
how are differential white blood cells counted
can use automated blood anaylser- if abnormalities are detected then they will need to be counted manually on a blood film
what causes abnormal differential white blood cells
infection
allergic reactions
packed cell volume (PCV)
- Proportion of blood that is made up of RBC
- Centrifuged blood allows visualisation
what can overestimate Hb results
- Turbidity (is the cloudiness or haziness of a fluid) of plasma can overestimate Hb measurement
what can underestimate Hb results
in vitro haemolysis
Red cell distribution width (RDW)
- Variation in size of the RBC
- If increased= anisocytosis (patient’s red blood cells are of unequal size. This is commonly found in anemia and other blood conditions.)
Red cell distribution width (RDW) can be used to assess
anaemia
- Increased in iron deficiency
- First parameter to rise as iron stores fall
- Usually normal in thalassaemia trait
- Increased following transfusion
