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PPS - cancer > Blood tests > Flashcards

Blood tests Flashcards

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
Q

When is a FBC requested?

A

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

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26
Q

What conditions do FBC monitor?

A

Infection

Anaemia

Diagnose and monitor haematological malignancies

Different cells in the blood are investigated to detect underlying conditions:

  • Leukaemia
  • Hodgkin’s disease
  • Myeloma
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27
Q

How to undertake a FBC?

A

Sample: 4ml whole blood collected in an EDTA (lavender top) tube

Test: FBC is conducted on an automated haematology counter

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28
Q

What are examples of modern counters?

A

Fluorescence flow cytometry - count WBC

Electrical impedence - count RBC and platelets

Colorimetric assay - measure haemoglobin concentration

29
Q

Describe the process of fluorescence flow cytometry

A

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
Q

How could WBC differential scattergram be used for diagnosis?

A

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
Q

Describe the process of electrical impedance

A

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
Q

Describe the process of colorimetric assay

A

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
Q

What is SLS (sodium lauryl sulphate)?

A

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
Q

What parameters are used to measure anaemia?

A

Haemoglobin

Size of RBC

35
Q

What are the types of anaemia?

A

Macrocytosis

Microcytosis

36
Q

What is macrocytosis?

A

Raised red cell volume

Indicates

  • Vitamin B12/ folate deficiency
  • ethanol
  • hypothyroidism
37
Q

What is microcytosis?

A

Reduced cell volume

Indicates

  • iron deficiency
  • thalassaemia trait
38
Q

What are ways to investigate WBC?

A

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
Q

What is microcytic anaemia?

A

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
Q

What is a blood film?

A

Look at blood under the microscope

Blood films are made by smearing a drop of anticoagulated venous blood onto a glass slide

41
Q

How are blood films prepared?

A

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
Q

Who looks at blood films?

A

Laboratory scientists

Alert the on-call haematology doctors if serious abnormalities are identified

43
Q

What is hypochromia?

A

Lack of the characteristic red colour of RBC

Only a rim of haemoglobin is present at cell peripheries

44
Q

What is iron deficiency microcytic anaemia characterised by?

A

Microcytosis

Hypochromia

45
Q

Should FBC results be conclusive?

A

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
Q

What happens with abnormal results in FBC?

A

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
Q

What are liver function tests?

A

Collection of tests that measured the concentration of certain proteins and enzymes in the blood

Provide information about the state of the liver

48
Q

How do we carry out liver function tests?

A

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
Q

What are precautions that have to be taken when taking blood for LFTs?

A

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
Q

Are raised bilirubin levels evident clinically?

A

No

Above 50 microm = jaundice evident clinically in sclera and skin

51
Q

Why can bilirubin be raised?

A

Problem with liver function

Problem with excretion

May be raised in metastatic liver cancer

52
Q

Why can albumin levels be low?

A

Low due to liver function disrupted by cancer

Liver synthesised albumin

53
Q

Why can AST and ALT levels be raised?

A

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
Q

What are urea and electrolytes used to measure?

A

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
Q

Where are lab tests run?

A

In Clinical Biochemistry labs

Run on automated analysers

56
Q

How do automated analysers work?

A

Formed by modules

Connected to carry out different types of assay

Use colorimetric assays

57
Q

What is a colorimetric assay?

A

Utilise reactions involving a colour change which can be measured using spectrophotometry

Can be used to measure lipids, drugs, proteins and enzymes

58
Q

Advantages of using automated analysers

A

High throughput testing - 600 tests/hr

Contactless ultrasonic mixing avoids sample contamination

59
Q

How are the biochemistry tests accomplished?

A

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
Q

Why are urea and electrolytes tested?

A

Provide information about kidney function

61
Q

How are urea and electrolyte testing carried out?

A

5 ml of venous blood - serum or plasma

Carry out colourimetric and ISE assays

62
Q

How can urea levels be used to indicate pathology?

A

Raised due to

  • impaired kidney function
  • dehydration
  • GI bleeding - digestion of own blood
63
Q

How can creatinine levels be used to indicate pathology?

A

Impaired kidney function

64
Q

Why does impaired kidney function raise the levels of waste products in the blood?

A

If kidney function decreases, excretion of waste products decreases and concentration in the blood increases

65
Q

What is Na+ used for in the body?

A

Required for

Fluid balance
Membrane potential
Nerve and muscle function

66
Q

What is K+ used for in the body?

A

Required for

Membrane potential
Nerve and muscle function

Small changes can lead to changes in heart rhythm

67
Q

What is Cl- used for in the body?

A

Required for

Fluid balance
Acid-base balance

68
Q

What can creatinine be used for?

A

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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