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PPS - cancer > Blood tests > Flashcards

Blood tests Flashcards

(68 cards)

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1
Q

On what type of blood are tests performed on?

A

Venous blood

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2
Q

How is venous blood collected?

A

Venepuncture

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3
Q

What is a vacutainer?

A

Evacuated tube system used to perform venepunctures

Vacuum inside

Automatically extract the exact volume of blood needed

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4
Q

Who collects blood samples?

A

Phlembotomists

Junior doctors or nurses collect the blood if patient is feeling unwell

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5
Q

What is an advantage of using vacutainers?

A

Only one needle needed

Change from one vacutainer to the next

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6
Q

What is the procedure of collecting blood using vacutainers?

A

Appropriate vacutainer is pushed into the needle-holder

Blood flows into the tube as it fills the vacuum

Once filled, the tube is removed

Another vacutainer can be inserted into the same vacutainer

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7
Q

What system is used to organise the vacutainers?

A

Vacutainers are colour-coded according to which additives they contain

DIfferent additives react with the blood differently

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8
Q

What are the different additives added to the vacutainers?

A

EDTA - purple

Sodium or Lithium Heparin - green

Sodium citrate - blue

Sodium or Ammonium Oxalate - yellow

Sodium fluoride - yellow

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9
Q

What does the purple top represent?

A

EDTA

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10
Q

What does the green top represent?

A

Sodium or Lithium Heparin

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11
Q

What does the blue top represent?

A

Sodium Citrate

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12
Q

What does the yellow top represent?

A

Sodium or Ammonium Oxalate

Sodium Fluoride

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13
Q

What is EDTA used for?

A

Anticoagulant

Chelates calcium (enzyme cofactor essential in the clotting cascade)

Used in full blood count tests

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14
Q

What is Sodium or Lithium Heparin used for?

A

Anticoagulant

Inhibits thrombin formation

Used in chemistry tests requiring plasma samples

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15
Q

What is Sodium Citrate used for?

A

Anticoagulant

Precipitates calcium

Used in coagulation studies

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16
Q

What is Sodium or Ammonium Oxalate used for?

A

Anticoagulant

Precipitates calcium

Used for blood glucose measurement

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17
Q

What is Sodium Fluoride used for?

A

Inhibits glucose metabolism

Preserves glucose concentration

Used with Sodium/ Ammonium Oxalate for blood glucose testing

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18
Q

In which ways can blood testing differ?

A

Additives added

Part of the blood that is tested :

  • whole blood
  • plasma
  • serum
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19
Q

What are the three main fractions of blood?

A

Whole blood

Plasma

Serum

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20
Q

What is the process of testing whole blood?

A

Contains both cellular elements and plasma

Blood is collected into a tube containing and anticoagulant like EDTA

To prevent clotting

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21
Q

What is the process of testing plasma?

A

Blood is collected into a tube containing an anticoagulant such as heparin or EDTA

The sample is centrifuged

The supernatant formed following centrifugation is plasma

Plasma = whole blood - cellular elements

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22
Q

What is the process of testing serum?

A

Blood is collected into a plain tube and allowed to clot

The sample is centrifuged

The supernatant following centrifugation is serum

As the blood was allowed to clot first, serum does not contain clotting factors

Serum = plasma - clotting factors

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23
Q

What is supernatant?

A

Upper liquid layer formed when a suspension is centrifuged

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24
Q

What is centrifugation?

A

Blood samples are spin in a centrifuge at G-force of 1000

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25
When is a FBC requested?
A routine investigation The most frequently requested laboratory test Almost all patients will undergo these Measure parameters to do with different components of the blood
26
What conditions do FBC monitor?
Infection Anaemia Diagnose and monitor haematological malignancies Different cells in the blood are investigated to detect underlying conditions: - Leukaemia - Hodgkin's disease - Myeloma
27
How to undertake a FBC?
Sample: 4ml whole blood collected in an EDTA (lavender top) tube Test: FBC is conducted on an automated haematology counter
28
What are examples of modern counters?
Fluorescence flow cytometry - count WBC Electrical impedence - count RBC and platelets Colorimetric assay - measure haemoglobin concentration
29
Describe the process of fluorescence flow cytometry
Blood sample is diluted in buffer Labelled with a fluorescence marker that binds nucleic acids As cells flow through a narrow aperture they are illuminated by a laser beam Three signals are recorded for each cell: - Forward-scatter: indicates cell volume - Side-scatter: indicates cell content - Side-fluorescence: indicates amount of DNA and RNA Cells with similar physical and chemical properties form a cluster in a scattegram Allows the differentiation of WBC
30
How could WBC differential scattergram be used for diagnosis?
Each dot represents one celll Coloured ovals indicate cells with similar properties Cell types can be distinguished and counted using these parameters Immature WBC have high fluorescence due to high nuclear activity High numbers of these cells could indicate leukaemia
31
Describe the process of electrical impedance
RBC are very poor electrical conductors Can be used to enable their measurement RBCs are diluted in an electrolyte solution They are then passed in a stream through a narrow aperture across which electrical current is maintained Individual cells create an increase in the electrical impedance of a size proportional to their volume
32
Describe the process of colorimetric assay
Sodium lauryl sulphate is used to lyse cells Heme group of Hb is oxidised, and SLS hydrophilic groups bind to form stable coloured complex Monochromatic light from an LED is absorbed by the SLS-HGB complexes The absorbance is measured by a photo-sensor Absorbance is proportional to the haemoglobin concentration of the sample
33
What is SLS (sodium lauryl sulphate)?
Common detergent used in cleaning products and laboratory applications Lyses both RBC and WBC Denatures proteins by disrupting non-covalent bonds and swamping proteins with negative charge
34
What parameters are used to measure anaemia?
Haemoglobin Size of RBC
35
What are the types of anaemia?
Macrocytosis Microcytosis
36
What is macrocytosis?
Raised red cell volume Indicates - Vitamin B12/ folate deficiency - ethanol - hypothyroidism
37
What is microcytosis?
Reduced cell volume Indicates - iron deficiency - thalassaemia trait
38
What are ways to investigate WBC?
Can indicate infection and haematological malignancies Number of WBC Look at differential subset and determine which one is abnormal Can look at the appearance of the WBC by blood films
39
What is microcytic anaemia?
Low RBC but normal WBC Small RBC and low haemoglobin To find out underlying cause - conduct more tests: - iron deficiency test - blood film - look at cells under the microscope
40
What is a blood film?
Look at blood under the microscope Blood films are made by smearing a drop of anticoagulated venous blood onto a glass slide
41
How are blood films prepared?
Blood films are dried, fixed with methanol and stained A common stain = May-Grunwald-Giemsa stain Automated preparation in hospital haematology labs Slides are checked to endure adequate staining Systemic visual inspection using light microscopy
42
Who looks at blood films?
Laboratory scientists Alert the on-call haematology doctors if serious abnormalities are identified
43
What is hypochromia?
Lack of the characteristic red colour of RBC Only a rim of haemoglobin is present at cell peripheries
44
What is iron deficiency microcytic anaemia characterised by?
Microcytosis Hypochromia
45
Should FBC results be conclusive?
The normal range is describe for where 95% of the healthy population lies This means 5% of the normal population will lie outside the normal range Therefore never look at blood test results in isolation - look in context with the clinical symptoms
46
What happens with abnormal results in FBC?
Abnormal results are usually assessed in more detail by making a blood film A repeat test would be conducted if the initial abnormal result is suspected to be artifactual
47
What are liver function tests?
Collection of tests that measured the concentration of certain proteins and enzymes in the blood Provide information about the state of the liver
48
How do we carry out liver function tests?
5 ml of venous blood or plasma No undue delay in preparing it Can be sampled at any time - no need for patient preparation
49
What are precautions that have to be taken when taking blood for LFTs?
Using a tourniquet during a venipuncture should be avoided if possible, as this can cause falsely raised albumin levels Bilirubin is broken down during exposure to light, so the blood sample should also be protected from the light
50
Are raised bilirubin levels evident clinically?
No Above 50 microm = jaundice evident clinically in sclera and skin
51
Why can bilirubin be raised?
Problem with liver function Problem with excretion May be raised in metastatic liver cancer
52
Why can albumin levels be low?
Low due to liver function disrupted by cancer Liver synthesised albumin
53
Why can AST and ALT levels be raised?
Raised as the damage to the hepatocytes make the enzymes leak out of the cells into the blood ALT can be highly increased with liver 5x normal
54
What are urea and electrolytes used to measure?
Used to measure kidney function Levels are closely controlled by the kidneys Any disturbance to the kidneys function will cause abnormal levels of these
55
Where are lab tests run?
In Clinical Biochemistry labs Run on automated analysers
56
How do automated analysers work?
Formed by modules Connected to carry out different types of assay Use colorimetric assays
57
What is a colorimetric assay?
Utilise reactions involving a colour change which can be measured using spectrophotometry Can be used to measure lipids, drugs, proteins and enzymes
58
Advantages of using automated analysers
High throughput testing - 600 tests/hr Contactless ultrasonic mixing avoids sample contamination
59
How are the biochemistry tests accomplished?
Automated process Blood samples are labelled and barcoded The barcodes are scanned by the analysers and contain the information about which tests run Some large laboratories contain tracks along which samples are moved around to various test stations
60
Why are urea and electrolytes tested?
Provide information about kidney function
61
How are urea and electrolyte testing carried out?
5 ml of venous blood - serum or plasma Carry out colourimetric and ISE assays
62
How can urea levels be used to indicate pathology?
Raised due to - impaired kidney function - dehydration - GI bleeding - digestion of own blood
63
How can creatinine levels be used to indicate pathology?
Impaired kidney function
64
Why does impaired kidney function raise the levels of waste products in the blood?
If kidney function decreases, excretion of waste products decreases and concentration in the blood increases
65
What is Na+ used for in the body?
Required for Fluid balance Membrane potential Nerve and muscle function
66
What is K+ used for in the body?
Required for Membrane potential Nerve and muscle function Small changes can lead to changes in heart rhythm
67
What is Cl- used for in the body?
Required for Fluid balance Acid-base balance
68
What can creatinine be used for?
Used to calculate an estimated GFR Cockroft Gault Equation For males multiply answer by 1.2 For females multiply answer by 1.04 For those of Black-African origin multiply answer by 1.18

PPS - cancer (6 decks)

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