Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MSC: Analytical Methods > Principles of Analysis > Flashcards

Principles of Analysis Flashcards

1
Q

What is a definitive method?

A

A method of exceptional scientific accuracy suitable for certification of reference material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a reference method?

A

A method demonstrating small inaccuracies against definitive method

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a Routine Method?

A

Method deemed sufficiently accurate for routine use against reference method and standard reference materials (SRM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are examples for Cholesterol?

A

Definitive Method: ID/GC/MS Isotope dilution/gas chromatography/mass spectrometry

Reference: Abell-Kendall method

  • Hydrolysis of cholesterol esters with alcoholic KOH
  • Extraction of total cholesterol with hexane for 15mins -> dried in vacumn
  • Treated with acetic acid/acetic anhydride/sulphuric acid 30mins ->Abs 620nm

Routine Method: Enzymatic Method

  • Cholesterol esters + cholesterol esterase → free cholesterol
    • Cholesterol oxidase → cholestene-3-one + H2O2
    • 4-aminoantipyrine + phenol → red quinoneimine dye Abs 540/600nm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a Primary Standard?

A

A substance of known chemical composition and high purity that can be accurately quantified and used for assigning values to materials and calibrating apparatus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a Standard Reference Material?

A

Reference material issued by an institute whose values are certified by a reference method which establishes traceability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the secondary standard?

A

A commercially produced standard for routine use calibrated against a primary standard or reference material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the internal standard?

A
  • A substance not normally present in the sample. Added to both standard and sample to correct for variation in conditions between different samples run – e.g. HPLC, GC, MS.
  • The internal standard is also used to verify instrument response and retention time stability.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are Calibrator Requirements?

A
  • Prepared from pure substance
  • Stable and homogenous material
  • Matrix similar to assay matrix e.g. serum
  • No chemical interferences
  • If possible should be obtained commercially to minimise error
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are calibrator values?

A

Commercially available calibrators have a concentration with a particular value:

  • Stated value – no certification
  • Assigned value – given arbitrarily or derived using a non-reference method
  • Certified value – certification of value by particular institute or body
  • Standard Reference Method TM value – derived used a reference method
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is Traceability?

A

An unbroken chain of comparisons of measurements leading to a reference value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What makes a Good method?

A
  • Analytical Accuracy: Measure of agreement between a measured quantity and true value
  • Analytical precision: Measure of agreement between replicates
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why is accuracy and precision required for result to be effective clinically?

A
  • Precision is important for following course of disease/monitoring therapy i.e. reproducibility
  • Accuracy is important for diagnosis since measured value is compared to reference range
  • For screening precision and accuracy are important to avoid false positives and false negatives
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is verification and validation?

A
  • Verification – confirmation, through provision of objective evidence, that the specified requirements have been fulfilled.
  • Validation – confirmation, through provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What guidelines are used in the assessment of assay performance?

A

ISO 15189 : 2012 Medical laboratories – Requirements for quality and competence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is trueness?

A
  • Difference between true and measured value
  • The measure of trueness is systematic error or bias
  • The idea is that a measurement is true when it is aimed squarely at the centre
  • Trueness and precision are independent of one another
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How is Trueness measured?

A
  • Repeat analysis of multiple levels of certified reference materials.
  • Results are compared with the assigned value
  • Recovery experiments
  • Comparison with results from “fresh” EQA material
  • Correlation with a current/accepted method using patient samples (comparability)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is Precision?

A
  • Results are clustered
  • The degree of precision can be measured by quantifying the overall effect of all random errors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How is Precision measured?

A
  • Repeatability: Minimum 20 results obtained from repeat analysis of IQC and patient samples on the same run Intermediate
  • Precision: Minimum 20 results obtained from repeat analysis of IQC and patient samples from runs on different days
20
Q

What is the equation for Precision?

A

​​Coefficient of variation (CV)= [SD/M] x 100%

  • Advantage of being unit-less
  • Allows comparison between results from different analytes in a way standard deviation cannot be Ideal CV <5% and no worse than 10% except at low levels
21
Q

What is Accuracy?

A
  • Accuracy is a combination of trueness and precision
  • Accuracy therefore involves systematic and random error
22
Q

How is Accuracy measured?

A

Total Error

Estimate the TE and therefore accuracy by combining:

  • Estimate of bias from method comparison / EQA
  • Estimate of precision from replication studies (intermediate precision)

TE = bias + 2 SD

23
Q

What is measurement uncertainty?

A
  • A parameter associated with the result of a measurement, that characterises the dispersion of the values that could be reasonably attributed to the measurand.
24
Q

How is Measurement uncertainty assessed?

A
  • The basic parameter of Measurement Uncertainty is standard deviation
  • Best estimate of the “true value” ± measurement uncertainty (2xSD from intermediate precision)
25
Q

What is interference?

A

The effect on the analytical measurement of a particular component by a second component

26
Q

What are types of Interferences?

A

Analytical

  • Cross-reactivity with other compounds
  • Interference in methodology e.g. increase in absorbance due to lipaemia

Physiological

  • Drugs e.g. prolactin increased by antipsychotics
27
Q

What is Analytical Specificity and Sensitivity?

A
  • Analytical Specificity: Measure of a method to determine only the analyte of interest i.e. cross-reactivity
  • Analytical sensitivity: Ability of a method to detect small concentrations
28
Q

What is the Limit of Blank?

A
  • Highest measurement result that is likely to be observed (with a stated probability) for a blank sample
29
Q

What is Limit of Detection?

A
  • Lowest amount of analyte in a sample that can be detected with (stated) probability, although perhaps not quantified as an exact value
30
Q

What is Limit of Quantification?

A
  • Lowest amount of analyte in a sample that can be quantitatively determined with stated acceptable precision and trueness under stated experimental conditions
  • Functional sensitivity is the analyte concentration at which the method CV = 20% or some other pre-determined CV
31
Q

What is Functional Sensitivity?

A

Functional sensitivity is defined as the lowest concentration that can be measured with acceptable intermediate precision [CV]

32
Q

What is the measuring interval?

A
  • The interval between the upper and lower concentration of analyte in the sample for which it has been demonstrated that the method has suitable levels of precision, accuracy and linearity
  • Range between the LOQ and the highest concentration studied during verification/ validation. Determined by linearity
33
Q

What is linearity?

A
  • An assessment of the difference between an individual’s measurements and that of a known standard over the full range of expected values
  • Usually performed by comparing results from a series of dilutions of known standard across assay range
34
Q

How is reference range determined?

A
  • If the concentration of a particular analyte is measured in samples from a normal healthy population (n>120) then a range of results is obtained
  • If plotted as a frequency plot a Gaussian distribution is usually observed (may be normal or skewed)

If you measure an analyte in 20 people how many will be outside of the reference range? 1 in 20 or 5%

35
Q

How is reference range calculated?

A
  • Parametric method: Assume Gaussian distribution of data or transformed (log) data. Determine reference limits (percentiles) as +/- 2SD from mean
  • Non-parametric method: Makes no assumption about type of distribution. Results ranked and cut-off taken at x% of values in each tail
  • Target driven reference range: e.g. cholesterol: reference range cannot be derived from “healthy” population. JBS2 targets for treatment of hyperlipidaemia
36
Q

What are exclusion criteria for reference ranges?

A
  • Diseases
  • Risk factors
  • Obesity
  • Hypertension
  • Genetically or environmental
  • Intake of pharmacological agents
  • Medication
  • Oral contraceptive
  • Drug abuse
  • Alcohol
  • Tobacco
  • Physiological states
  • Pregnancy
  • Stress
  • Excessive exercise
37
Q

What is Biological Variation?

A
  • Results used to derive a reference range contain elements of both analytical and biological variation
  • Biological variation introduced by physiological factors, diet, fluid intake, exercise
38
Q

What is the equation for biological variation?

A
  • CV (total) = √ (CV^2analytical + CV^2biological)
39
Q

What is clinical sensitivity and clinical specificity?

A
  • Clinical Sensitivity – The ability of a TEST to correctly identify those who HAVE the disease A highly sensitive tests has few false negatives
  • Clinical Specificity – The ability of a TEST to correctly identify those who do NOT HAVE the disease A highly specific test has few false positives
40
Q

What is Predictive value and diagnostic efficiency?

A
  • Predictive value (+/-) = measure of the ability of test to correctly assign individual to either disease or non-diseased group
  • Diagnostic efficiency = proportion of true results
41
Q

What is an equation for Sensitivity?

A
  • Sensitivity = True Positives / (True Positives + False Negative)
42
Q

What is an equation for Specificity?

A
  • Specifity = True Negatives / (True Negatives + False Positives)
43
Q

What is Positive Predictive Values and Negative Predictive Values?

A
  • Positive Predictive Value (PPV): The ability of a test to detect the presence of disease
  • Negative Predictive Value (NPV): The ability of a test to detect the absence of disease
44
Q

What can affect predictive values?

A
  • Predictive Values ARE affected by prevalence
  • As disease prevalence increases the PPV also increases
  • As disease prevalence decreases the NPV increases
45
Q

What is the equation for Positive Predictive Value?

A

Positive Predictive Value = True Positive / (True Postive + False Positive):

46
Q

What is the equation for Negative Predictive Value?

A
  • Negative Predictive Value = True Negative / (True Negative + False Negative)
47
Q

What are Cut-Off Values?

A
  • Often diagnostic test results and associated clinical outcome are NOT naturally binary (either positive or negative) but continuous
  • For test results that are continuous variables a clinical threshold/cut-off values have to be applied to classify test results as being positive or negative

MSC: Analytical Methods (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions