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DEN 2027 - Disease Mechanisms > Diagnosis > Flashcards

Diagnosis Flashcards

1
Q

Name 4 reasons to diagnose

A
  1. Identify aetiological agent
  2. Immunity to infection
  3. Prognosis
  4. Epidemiology
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2
Q

What are 3 components of prognosis?

A
  1. Monitor response to treatment
  2. Monitor and prevent infection
  3. Detect antiviral resistance
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3
Q

Describe the diagnostic chain

A
  • Clinical indication
  • Specimen collection
  • Specific request
  • Transport to Lab
  • Logged-in
  • Initial processing
  • Test procedure
  • Data retention
  • Result authorisation
  • Report generation and transfer
  • Clinical action
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4
Q

What 2 things can be involved in processing a sample?

A
  1. Inactivating virus present

2. Spinning down blood

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5
Q

Why is specimen collection one of the most important step in diagnosis?

A

Results of diagnostic tests for infection diseases are dependent on selection, timing and method of collection

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6
Q

Name 4 important test characteristics

A
  1. Sensitivity
  2. Specificity
  3. Positive predictive value
  4. Negative predictive value
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7
Q

What is sensitivity of a test?

A

Proportion of people with the disease who test positive

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8
Q

What is specificity of a test?

A

Proportion of people without the disease who have a negative test

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9
Q

What is positive predictive value of a test?

A

Proportion of people testing positive who actually have the disease

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10
Q

What is negative predictive value of a test?

A

Proportion of people testing negative who do not have the disease

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11
Q

What are 6 features of a good diagnostic test?

A
  1. Accurate
  2. Reliable
  3. Reproducible
  4. Timely
  5. Affordable
  6. Available
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12
Q

What are 5 methods of diagnostic microbiology?

A
  1. Microscopy
  2. Culture
  3. Immunological
  4. Molecular methods
  5. Point of care tests
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13
Q

How is immunological microbiology usually carries out?

A

Sample of blood

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14
Q

What are 3 types of microscopy?

A
  1. Light
  2. Fluorescent
  3. Eletron
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15
Q

Describe 3 things to look for during light microscopy

A
  1. Staining characteristics
  2. Shape
  3. Size
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16
Q

What is fluorescent microscopy?

A

Specimens stained with fluorescent dye which emits light when excited under fluorescent microscope e.g. auramine staining of TB bacilli

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17
Q

Describe electron microscopy

A
  • Uses electron beam to produce magnified image
  • Achieves better resolution and magnifications
  • Limited sensitivity, expensive and specialist
  • Diagnosis of smallpox (bioterrorism)
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18
Q

What are 3 characteristics of bacteriological culture growth?

A
  1. Clinical specimen inoculated onto various media
  2. Appearance of colonies suggest species presence
  3. Further tests to clarify
19
Q

What 3 ways can provide various media for inoculation?

A
  1. Selective agar
  2. Nutrient enrichment
  3. Incubation at different temperatures and atmospheres
20
Q

What type of bacteriological culture can help identify streptococci?

A

Haemolysis as pathogen lysis red blood cells

21
Q

Describe how antimicrobial sensitivities can be tested on an agar plate

A
  • Filter paper disc is impregnated with antibiotic
  • Incubate bacteria on agar with discs placed on top
  • Area of zone of inhibition around the disc shows sensitivity
22
Q

What does a VITEK identification card consist of?

A

30 wells each containing biochemical substrates in a dehydrated form

23
Q

What does a VITEK susceptibility testing card consist of?

A

30 or 45 wells containing dehydrated antibiotics with specific tests for detecting resistance mechanisms are systematically included

24
Q

What does MALDI-TOF stand for?

A

Matrix-assisted laser desorption/ionization time-of-flight

25
Q

What is MALDI-TOF Mass Spectrometry?

A

Ionization method which uses a laser energy absorbing matrix to create ions from large molecules with minimal fragmentation

26
Q

Describe the 3 step process of MALDI-TOF Mass Spectrometry

A
  • Sample is mixed with suitable matrix material and applied to metal plate
  • Pulsed laser irradiates sample, triggering ablation and desorption of sample and matrix
  • Analyte molecules ionized in the hot plume of ablated gases, and can be accelerated into whichever mass spectrometer is used to analyse them
27
Q

Describe the bacteriological diagnosis of streptococcal pharyngitis

A
  • Throat swab
  • Complete haemolysis on blood agar
  • Latex agglutination typing test
28
Q

Describe the bacteriological diagnosis of candida albicans

A
  • Culture in germ tubes
29
Q

Describe 2 forms of bacteriological diagnosis of dermatophyte infections

A
  • Direct microscopic examination of scales dissolved in KOH

- Culture of scrapings of lesions

30
Q

What are 5 characteristics of serology?

A
  • Testing for specific microbial antigens
  • Direct detection from clinical specimens
  • Characterization of cultured organism
  • Testing for antibody to specific microbial antigens
  • Detection of particular isotope (IgM or IgG)
31
Q

What different types of infection are suggested by presence of IgM or IgG isotopes in serolgy?

A
  • IgM suggests acute infection (IgG may or may not be present)
  • IgG suggests long term or past infection (IgM will not be present)
32
Q

How is serological technique carried out?

A
  • Add specific viral antigen to patient serum
  • If virus specific antibody is present an antigen-antibody complex will form
  • Indicator system is used to detect if complex has formed
33
Q

What is an enzyme immunoassays?

A

Anti-human antibody combined with enzymes which will react with antigen to produce a colour change

34
Q

What is the incubation period of a virus?

A

Time to onset of symptoms

35
Q

What is the window period of a virus?

A

Time between start of symptoms and development of an antibody

36
Q

Why is a blister swabbed in chicken pox and not blood?

A
  • It takes 14 days for an onset of symptoms so if blister swabbed at 14 days virus is present
  • It takes 19 days for an antibody to be produced so if blood sample taken before 19 days negative test will occur
37
Q

Name 2 main types of molecular techniques used to detect viral genomes

A
  1. Real-time PCR

2. Sequencing and next generation sequencing

38
Q

What are 3 characteristics of real time PCR?

A
  • Allow detection and quantification of DNA sequence based on use of fluorescent reporter
  • Fluorescence is measured during each cycle and is proportional to amount of PCR produce
  • No genome present means fluorescence does not occur / Lots of virus present means lots of fluorescence
39
Q

Describe the steps of real time PCR

A
  • Specific probe to sequence within PCR product is labelled with reporter dye on one end and quencher dye on the other
  • Taq polymerase come across bound probe
  • 5’ exonuclease degrades probe releasing reporter dye to fluoresce
40
Q

What is DNA sequencing?

A

Process of determining nucleic acid sequencing, including any method or technology used to determine the order of the four nucleotides in DNA

41
Q

What is NGS?

A

Next generation sequencing which is the catch-all term used to describe a number of different modern sequencing technologies

42
Q

What is point of care testing?

A

Diagnostic testing at or near the point of care i.e. at the time and place of patient care (not labratory)

43
Q

Give 4 examples of POCTs

A
  1. HIV testing in GUM clinics
  2. Helicobacter pylori testing in endoscope clinics
  3. Influenza testing in A&E
  4. Strep throat
44
Q

What is the main advantage of POCTs?

A

Faster results for better patient management

DEN 2027 - Disease Mechanisms (20 decks)

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