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Year 2 MCD 2 > Diagnostics > Flashcards

Diagnostics Flashcards

1
Q

What are the most commonly requested tests for metabolites?

A

1) Full Blood Count (FBC), Erythrocyte Sedimentation Rate (ESR), C-reactive Protein (CRP)
2. Liver function tests (LFT)
3. Urea and Electrolytes (U&E)
4. Blood Glucose
5. Investigation of Vital Illness
6. Stool culture-bacteriology

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2
Q

What does a U&E test show?

A

Measures Na+, K+, Urea and Creatinine

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3
Q

What are creatinine levels a measure of?

A

Creatinine is a measure of glomerular filtration rate (GFR) as it is excreted by the kidneys at a fixed rate.

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4
Q

What is measured by Liver Function Test?

A

Levels of:

  • albumin
  • total bilirubin (TBL)
  • alkaline phosphatase (ALP)
  • alanine amino-transferase (ALT)
  • Aspartate amino-transferase (AST)
  • Gamma glutamyl transferase
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5
Q

What cardiac proteins are measured in the blood?

A
  • troponin
  • creatine kinase
  • AST (Aspartate amino-transferase)
  • lactate dehydrogenase
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6
Q

What causes a heamolysed sample of blood?

A

A haemolysed sample is due to damage to erythrocytes because of incorrect needle size. This causes K+ to leak into the plasma so results will show very high K+. When centrifuged, plasma will appear pink indicating haemolysis.

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7
Q

How can you tell a sample has been haemolysed?

A
  • high K+

- pink plasma when centrifuged

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8
Q

What is the difference between serum and plasma?

A

Serum is that part of blood which is similar in composition with plasma but excludes clotting factors of blood.

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9
Q

What do the blood sample collecting tubes with:
- Red
- Yellow
- Purple
caps contain? What tests are these useful for?

A
  • Red contains nothing. Useful for U&E, TFT (thyroid), LFT (liver)
  • Yellow contains a Gel to speed clotting. Useful for U&E, TFT (thyroid), LFT (liver).
  • ** The above two are allowed to clot as this allows collection of SERUM (not plasma) ***
  • Purple contains potassium EDTA which is an anticoagulant. This is useful for a FBCs, Blood Films and measuring HbA1c
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10
Q

What do the blood sample collecting tubes with:
- Green
- Grey
- Blue
caps contain? What tests are these useful for?

A
  • Green: Lithium heparin for detection of Homocysteine
  • Grey: contains fluoride oxalate for glucose test
  • Blue: contains citrate (an anti-coag) for clotting factor tests.
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11
Q

What non-laboratory tools are used to diagnose viral illnesses?

A

The tools we use to diagnose viral illnesses are primarily the history and physical examination. [This can be used to easily diagnose some infections such as shingles and chicken pox. However, in other cases the signs and symptoms may be more subtle and require the assistance of a virology laboratory.]

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12
Q

What evidence of viral infection can be detected by a laboratory (and how)?

A
  • Virus itself: virus isolation in cell culture and electron microscopy; ]slow and costly - replaced by PCR.]
  • Protein components (antigens) of the virus: Detected using immunofluorescence or enzyme immunoassays. Serotyping also allows to identify the subtype of the particular virus, which is important in HIV.
  • Genetic components of the virus: DNA or RNA through PCR.
  • The host response: antibody or cell responses (serology: the study of serum and their contribution to the protection of the body)
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13
Q

Differentiate between assey sensitivity and specificity?

A

Sensitivity is the test’s ability to correctly identify positive samples.
Specificity is the test’s ability to correctly identify negative samples.

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14
Q

How can we quantify the extent of viral infection?

A
  • Quantification of antibodies or antigens

- Quantification of genome to indicate viral load

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15
Q

What does the type of antibody produced by the immune system say about the duration of infection?

A

IgM is a marker for recent infection. A positive IgG result indicates infection or immunisation at any point in the past (life long duration), while the IgM will only be present for 3 months.

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16
Q

How does antibody avidity testing help in investigating a viral infection?

A

Antibody avidity testing provides a method for conforming positive IgM results. A low avidity index reflects recent infection. As there is maturation of antibody response over time, a high avidity index reflects an older infection.

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17
Q

What test(s) do we use to screen for HIV in the UK?

A

In the UK, we screen for HIV using chemiluminescence before confirming with an Enzyme Immunoassay (EIA) which is used to detect HIV antibodies (Ab) or p24 antigens (Ag).

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18
Q

Why are EDTA blood samples requested for all newly diagnosed HIV+ patients?

A

To measure viral load, genotyping and baseline resistance testing.

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19
Q

From when is HBV detectable?

A

The surface antigen of HepB Virus (HBV) is detectable from two weeks while it takes 6 weeks - 6 months for patients to become symptomatic.

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20
Q

From when is HCV detectable?

A

PCR can detect HepC Virus 1-2 weeks post-infection, while serology takes 9 weeks to become positive. Patient presents 3 weeks - 3 months post-infection.

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21
Q

What types of specimens are used for the detection of respiratory viruses?

A

Throat swab, Nasopharyngeal aspirate (NPA), bronchoalveolar lavage (BAL), Endotracheal (ET) secretions can be used for detection of respiratory viruses. For respiratory viruses, always use PCR.

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22
Q

What type of specimens are used for the detection of rotavirus, adenovirus and norovirus?

A

Stool sample (also urine for adenovirus)

23
Q

What viruses can be detectable from CSF?

A

herpes viruses and enteroviruses

24
Q

How is EDTA blood useful in viral investigations?

A

For viral load testing and detect viruses

25
Q

How is clotted blood useful in viral investigations?

A

Used for serology (antibody detection)

26
Q

How is saliva useful in viral investigation?

A

Saliva can also be used for serology and/or PCR

27
Q

How long do microbiology samples take to be cultured?

A

24-48h to produce results.

28
Q

What bacteria take longer than usual to culture?

A

Mycobacterium tuberculosis, Brucella, and Actinobacteria

29
Q

How can we test what antibiotics would be best against a bacterial infection?

A

Antimicrobial Susceptibility Testing done by:

  • The Minimum Inhibitory Concentrations (MIC/MBC test) is the least amount of drug required to inhibit growth of the bacteria. Compare the MIC to the table that gives values for resistance and sensitivity.
  • The Disc Diffusion is the zone of inhibition surround antibiotic discs on bacterial plate. If the value is above that in the table, the drug is effective at killing the bacteria, while if the value is below, the drug is not effective.
30
Q

Describe how Gram staining works

A

The Gram stain is the most important initial step.
Gram-positive bacteria will have a thick peptidoglycan cell wall which will take up the colour of the gram stain - purple. While Gram-negative bacteria have a thin peptidoglycan cell wall but also an outer lipopolysaccharide and phospholipid membrane. The out membrane is dissolved with the addition of alcohol and so does not retain the purple dye, and the weak counter-stain of safranin shows instead as a red colour.

31
Q

Are Gram positive or Gram negative bacteria more difficult to treat and why?

A

A lot of antibiotics work by targeting the peptidoglycan cell wall as we don’t have such a structure. Gram negative bacteria are often quite resistant as the antibiotic has to get through the outer membrane.

32
Q

What are the main types of bacterial cellular morphology?

A

Rod-shaped = Bacillus
Spherical = Coccus
Other ones include spirochetes

33
Q

What bacteria are:

  • Gram+ cocci that clump
  • Gram+ cocci that form chains
  • Gram- bacilli?
A

Gram+ cocci in clumps = Staphylococci (staph = grapes)

Gram+ cocci in chains = Streptococcii

Gram- bacilli = Escherichia coli

34
Q

Describe the test that can be used to identify strains of staphylococci

A

A coagulase test can be used to identify the strain of staphylococcus. A positive coagulase test indicates S. Aureus, while a negative one indicates S. epidermidis or S. saprophyticus.
This is important as Staphylococcus Aureus (including MRSA) can cause severe infections.

35
Q

Describe the test that can be used to identify strains of streptococci

A

Some pathogens produce hameolysins, which lyse blood-containing media in a process called haemolysis. This can be used to identify the type of streptococcus infections:

  • Alpha haemeolysis is a small zone of haemolysis and colonies can appear green. S. pneumoniae and S. mutans produce this type of haemolysis
  • Beta haemolysis is a large clear zone of haemolysis around the bacterial colonies. S. pyogenes, S. agalactiae and Enterococcus produce this pattern of haemolysis.
  • Gamma haemolysis is no haemolysis. Enterococcus and Peptostreptococcus produce this pattern of haemolysis.
36
Q

When is the optimal time to collect bacterial samples?

A

The optimal time of collecting the specimen is before starting the antimicrobials during the acute phase of the illness.

37
Q

At what temperature is a blood culture kept?

A

37 degrees C

38
Q

List three situations where histopathology and cytopathology might commonly be used as a diagnostic method.

A

The three main situations are for diagnosis, cancer staging and general monitoring of disease progression and treatment.

39
Q

What type of specimens are sent to histopathologists?

A
  • Biopsies - small piece of tissue taken to examine, and to inspect for cancers usually.
  • Resection Specimens
  • Frozen Specimens - This is used when surgeons need an urgent answer
  • Post-mortems
40
Q

What type of specimens are sent to cytologists?

A

Sputum
Body fluids which contain cells
Smears
Fine needle aspirates

41
Q

How are specimens prepared in a histopathologist’s lab?

A

Specimens must be properly labelled, and fixed in formalin (a preservative that stabilises protein binds and prevents autolysis). It is then embedded in paraffin wax before cut into sections.

42
Q

How long can a frozen section take to be analysed?

A

20 minutes

43
Q

How long do biopsies take to be analysed?

A

Biopsies take 2-3 days for larger specimens, or a day if a rapid diagnosis is required.

44
Q

How long do resection specimen take to be analysed?

A

A resection specimen takes longer at 5-7 days.

45
Q

What is immunohistochemistry commonly used for?

A

Immunohistochemistry (IHC) is an excellent detection technique and has the advantage of showing exactly where a given protein is located within the tissues. This is particularly useful when trying to identify the origin of difficult tumours, as the antibodies can bind to specific epithelial, mesochyme, prostate etc proteins.

46
Q

Summarise the benefits of the autopsy

A

Autopsies are performed to determine the cause of death of a patient, to explain why the treatment was unsuccessful. To show the spread of disease and to educate doctors regarding disease processes.

47
Q

List three benefits of cytology screening

A
  • If negative, can put the patient at ease
  • If positive, catching the cervical cancer earlier means it is more likely to respond to treatment
  • If positive, the patient can plan their life and make future decisions.
48
Q

How can antibodies used for diagnostic purposes be generated?

A
  • Antisera (pl of antiserum - blood serum containing antibodies against specific antigens) from immunised animals can be used for polyclonal antibody production
  • Monoclonal antibodies
  • Genetically engineered antibodies using recombinant DNA technology.
49
Q

How can monoclonal antibodies be made?

A

Monoclonal antibodies can be made by hybridoma fusion. Take antibody producing cells from immunised animals (limited life span) and fuse them to immortal myeloma cells. These fused cells will be able to produce antibody and be able to proliferate indefinitely.

50
Q

List the therapeutic uses of manufactured antibodies

A
  • Prophylactic protection against microbial infections
  • Anti-cancer therapy e.g anti-CD20 antibody for treating lymphoma
  • Removal of T-cells from bone marrow grafts (to avoid graft vs host diseases)
  • Block cytokine activity e.g anti-TNF treatment in rheumatoid arthritis.
51
Q

List the diagnostic uses of manufactured antibodies.

A
  • Tissue typing for transplantation
  • Blood group serology
  • Immunoassays: to quantitatively measure hormones, antibodies (anti-antibody) and antigens
  • Immunodiagnosis: diagnosing infectious diseases, autoimmunity, allergy and malignancy
52
Q

How can diagnostic antibodies be detected?

A
  • A serum electrophoresis sample can be used to detect an active immune response. A more densely antibody stained band at the top as there are more antibodies being produced therefore the person is not immunodeficient.
  • Flow cytometry can be used to detect the surface markers of different lymphocyte populations. This is done by adding fluorescently labelled antibodies before the cells are passed through a laser which then reflects a colour.
53
Q

What ‘reporters’ can be added to an antibody so that it can be detected?

A
  • Enzymes - e.g Peroxidase, Alkaline phosphatase cause colour change when the substrate binds to the enzyme.
  • Fluorescent probes - e.g dyes, beads of different sizes
  • Radioisotopes - these are not used as much due to environmental and safety reasons and also there are more sensitive methods available.
  • Magnetic beads
  • Coloured beads

Year 2 MCD 2 (5 decks)

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