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MELS301 > Laboratory Practice > Flashcards

Laboratory Practice Flashcards

1
Q

What are some examples of pre-analytical factors?

A

The test ordering system, patient/sample ID, patient preparation, specimen collection and transport.

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2
Q

What are some examples of analytical factors?

A

Reagents, calibration, QC, instrument and equipment maintenance.

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3
Q

What are some examples of post-analytical factors?

A

Result reporting, turn-around-time, critical value reporting and follow up.

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4
Q

What are some examples of non-analytical factors?

A

Staff competency and training, lab policies, SOP manuals, health and safety.

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5
Q

What do you want from a vein that you choose for venepucture?

A

Elasticity, large enough to support good blood flow, is well anchored by surrounding tissue, easily visible.

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6
Q

What are secondary sites in venepuncture?

A

Sites which are not ideal for blood draw but if necessary can be used such as if the patient doesn’t have arms, is covered in burns, or has very small veins. These include sites such as the hands, and sometimes feet as a last resort.

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7
Q

Why is flashback important?

A

So that the phlebotomist can visualise if they have gotten the needle into the vein before placing the tube in the vacutainer.

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8
Q

What are the pros and cons of butterfly needles?

A

They are smaller so they can get into small veins but because they have a small diameter there is a greater risk of haemolysis.

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9
Q

What are the health and safety standard precautions?

A

A set of practices to prevent the spread of infection between health workers and patients. Important to assume all blood and bodily substances are infectious until proven otherwise.

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10
Q

What is an influencing factor?

A

A factor that can cause a true change in analyte quantity method independent. These can be modifiable or unmodifiable.

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11
Q

What is a modifiable influencing factor?

A

If the patient is fed or fasting.

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12
Q

What is an unmodifiable influencing factor?

A

If the patient is diabetic.

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13
Q

What is an interfering factor?

A

A factor that can cause a false change in analyte quantity which may be method dependent.

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14
Q

What is an endogenous interfering factor?

A

Something that is occurring within the patients body. This could be something like in vivo haemolysis or lipaemia..

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15
Q

What is an exogenous interfering factor?

A

Something that occurs outside the body such as in vitro haemolysis, drugs given to the patient, cannula additives, tube gels or clots.

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16
Q

What is spectrophotometry?

A

The measured change in light absorbance as a beam of light focussed by a lens travels through the solution.

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17
Q

What occurs in small particle scattering?

A

The scattering particles largest dimension is less than 5% of the radiations wavelength so the scattering is symmetrical.

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18
Q

What occurs in large particle scattering?

A

The forward scattering increases and the backward scattering decreases. This is due to constructive and destructive interferences.

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19
Q

What is turbidimetry?

A

The detector is in line with the source and the decrease in transmitted light is measured. This is better for larger particles and higher concentrations.

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20
Q

What is nephlometry?

A

This is when the detector is at a 90 degree angle to the source and the scattered light is measured. This is better for smaller particles and lower concentrations.

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21
Q

What is haemolysis?

A

A membrane disruption of blood cells either RBC, WBC and platelets. This is the most common pre-analytical error affecting chemical pathology tests.

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22
Q

What is in vivo haemolysis?

A

Haemolysis that is occurring within the patients body.

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23
Q

What is the problem with in vivo haemolysis?

A

It is associated with decreased serum haptoglobin and increased urine Hb. There is no problem with these samples as it usually reflects the analyte level in the patient so the sample is not rejected.

24
Q

What is in vitro haemolysis?

A

When the cells are damaged during sample collection, handling or storage.

25
Q

Why is in in vitro haemolysis a problem?

A

The results in the tube wont match those in the patient so the sample may be rejected. The RBCs release their cell contents into the serum which can increase the concentration of analytes that are high inside the red cells.

26
Q

How does haemolysis cause spectrophotometric interference?

A

If there are absorption peaks at 415, 540 or 570nm analyte levels may be falsely decreased or falsely increased depending on analyte, method and severity of haemolysis.

27
Q

How does haemolysis cause sample dilution?

A

This is common in analytes which have higher concentrations extracellularly compared to intracellularly such as albumin, sodium and bilirubin. Haemolysis falsely dilutes these analytes.

28
Q

How does haemolysis cause chemical interference in assays?

A

They compete for binding sites or substrates inhibiting reactions.

29
Q

How does lipaemia interfere with tests?

A

It affects the turbidity of the sample due to light scattering by lipoproteins mainly chylomicrons and VLDL.

30
Q

How can lipaemia be reduced or eliminated?

A

By taking fasting samples 4-12 hours, ultra or high speed centrifugation in which lipids go to the top. Lipid clearing agents. These are not ideal because they add an extra step in the processing of samples.

31
Q

How does lipaemia cause interference spectrophotometrically?

A

The absorption decreases at wavelengths between 300 and 700nm. Light scattering interferes with turbidimetry and nephelometry.

32
Q

How does lipaemia cause volume depletion?

A

Lipid droplets take up volume in the aspirated sample so if you have more lipid you will have a smaller component of aqueous phase. This may falsely decrease the analyte of interest.

33
Q

How does lipid causes problems with partitioning the sample?

A

After centrifugation the lipid rises to the top of the sample which is where the machine takes its sample. This can be problematic with automated analysers.

34
Q

What is icterus?

A

High bilirubin levels causing a change in the colour of serum/plasma. Common in patients with liver disease, cancer and neonates.

35
Q

What nm does icterus cause interference spectrophotometrically?

A

400-540nm

36
Q

What is automated serum indicies?

A

It is used to detect and measure haemolysis, lipaemia, and icterus on every sample. Interference is graded into categories and unsuitable samples are flagged. They may be unsuitable for some tests but fine for others.

37
Q

What is bichromatic and polychromatic analysis?

A

An analytical method involving measurements at two or more wavelengths. You measure the absorbance at other wavelengths where there is no change in absorbance during the reaction.

38
Q

What is quality management?

A

The act of overseeing all activities and tasks needed to maintain a desired level of excellence. It includes quality assurance and quality control.

39
Q

What is quality assurance?

A

Policies and procedures, training, and equipment maintenance. This is done through IANZ accreditation, audits and keeping training records.

40
Q

What is quality control?

A

Inspecting quality through checks and tests, this is done by running control samples to make sure the testing system is working appropriately.

41
Q

What is analytical accuracy?

A

The closeness of mean test results to the true value (concentration) of the analyte.

42
Q

What is analytical precision?

A

The closeness of results from repeated analyses. This is expressed as the coefficient of variation.

43
Q

What is the coefficient of variation?

A

A standardised measure of spread that describes the amount of variability relative to the mean so the precision. This is often expressed as a percentage. It has no unit so is useful when comparing different data sets which have different units of measurement.

44
Q

What is analytical sensitivity?

A

The ability of an assay to detect small variations in concentration. The smallest amount a total protein test could detect for example.

45
Q

What is analytical specificity?

A

The ability of an assay to measure the target analyte in the presence of potentially interfering substances in the sample matrix. For example if you want to be testing for protein but your test is picking up lipid and calling it protein as well.

46
Q

What is the limit of detection?

A

The lowest value that significantly exceeds the measurement of a blank sample.

47
Q

What are reference values/intervals?

A

Values obtained from individuals randomly but appropriated selected in order to satisfy defined criteria. Most commonly contains the central 95% of values obtained for the reference population.

48
Q

What is calibration?

A

It determines the relationship between analyte concentration and instrument signal. A calibration curve should be prepared in the same biological matrix as the samples.

49
Q

What are quality control samples?

A

Samples of known acceptable values measured to ensure acceptable system performance. There are different types of materials available. They test different levels of interest such as normal or pathological. The westguard rules are used to determine acceptability. There is internal and external QC.

50
Q

What are the different types of quality control materials available?

A

Lyophilized, liquid stable, assayed, unassayed, qualitative, bi-level and tri-level.

51
Q

What is a lyophilized material?

A

A powder at the bottom of a vial, depending on the control you put it in deionized water.

52
Q

What is liquid stable material?

A

Liquids that last a long time.

53
Q

What is an assayed material?

A

A material that has already been tested and comes with all of the values you should get. You run it 5 to 10 times over 5-7 days to get an idea of a reference interval for the lab.

54
Q

What is a bi-level material?

A

A material that has two levels, high and low. So a pathological and a normal.

55
Q

What is a tri-level material?

A

A material that has three levels, a high, low, and normal.

MELS301 (10 decks)

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