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Year 2 MCD > Diagnostics > Flashcards

Diagnostics Flashcards

1
Q

Which anticoagulants are present in the tubes with red, yellow, purple, grey and blue tops?

A 
Red top = no anticoagulant
Yellow top = gel (procoagulant)
Purple top = potassium EDTA
Grey top = fluoride oxalate
Blue top = citrate
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2
Q

What is a purple-top tube used for?

A

Keeping cells alive.

Due to presence of potassium, can’t be used to measure electrolytes.

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3
Q

What is a grey-top tube used for?

A

Glucose testing. The fluoride oxalate is a poison which kills the erythrocytes, stopping the red cells performing glycolysis and preserving the glucose concentration in the sample.

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4
Q

What is the blue-top tube used for?

A

Measuring clotting factors in the blood

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5
Q

What is the difference between serum and plasma, and how would you produce serum?

A

Serum has no clotting factors in it: plasma has clotting factors.
To obtain serum, place sample in yellow or red-top tube (which don’t have any anticoagulant). The resulting clot can be removed to leave serum.

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6
Q

What is ESR?

A

Erythrocyte sedimentation rate - a measure of how quickly erythrocytes settle at the bottom of a test tube. A faster than normal (higher) ESR may indicate inflammation.

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7
Q

What are yellow/ red topped tubed used for?

A

Urea and electrolytes (U&E), thyroid function tests (TFTs), liver function tests (LFTs).

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8
Q

How do you obtain red cells and leave plasma?

A

Use a purple top tube - the anticoagulant (EDTA) prevents the clotting factors from being used. Erythrocytes will settle and can be separated from the plasma.

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9
Q

What proteins are measured in liver function tests?

A

Excess liver proteins in blood may indicate liver damage.
Enzymes measured: alkaline phosphatase (ALP), alanine amino-transferase (ALT), aspartate amino-transferase (AST), gamma glutamyl transferase (GGT).
Other proteins: albumin, bilirubin.

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10
Q

On an U&E, what does “HAEMOLYSED” next to the K+ measurement mean?

A

In poorly performed venepuncture, K+ can be released due to haemolysis, since erythrocytes contain lots of K+/ Instead of a yellow layer of plasma after centrifuge, you get a rose layer (free Hb).

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11
Q

Which markers rise in renal failure?

A

Urea and creatinine.

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12
Q

Which cardiac enzymes and proteins leak into the blood in cardiac damage, e.g. heart attack.

A

Troponins, creatine kinase (BM isoform), aspartate aminotransferase (AST) - also a liver enzyme - and lactate dehydrogenase (LDH).

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13
Q

In diagnostic virology, what types of things can we look for?

A

The infectious virus itself - virus isolation and electron microscopy.
Protein components of the virus (antigens).
Genetic components of the virus (DNA/RNA).
Host response (e.g. antibody).

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14
Q

Remind yourself of what the difference between a sensitive and specific test is.

A

Sensitive test: able to correctly identify positive samples.
Specific test: able to correctly identify negative samples.

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15
Q

What is “viral load”.

A

Quantification of the viral infection by determining the amount of viral genome in the blood.

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16
Q

Describe PCR briefly.

A

Use reverse transcriptase to form cDNA from RNA.
Denature at 95 degrees.
Cool to 50-60 to allow primer annealing.
Chain elongation at 72 using taq polymerase.

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17
Q

What is the main test in virology?

A

Serology testing (diagnostic identification of antibodies in serum).

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18
Q

What is the main test for detection of enteroviruses?

A

PCR - use a stool sample.

Vomit if necessary, but has a lower yield.

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19
Q

What are the common bacteriology diagnostic techniques?

A

Culture, serology, molecular techniques, susceptibility testing.
Susceptibility testing is the main reason we persist with culture.

20
Q

What is a blood culture bottle?

A

A bottle which a sample of blood can be put in whose bottom becomes YELLOW is positive - flagging infection up to the investigator.

21
Q

Describe what the gram stain test differentiates between.

A

Cell wall: gram positive has a thick peptidoglycan cell wall and only 1 membrane. Stains purple.
Gram negative has a thin wall and an outer lipopolysaccharide membrane (2 membranes). Stains pink.

22
Q

What is the coagulase test used for?

A

Differentiating between staphylococci.
Coagulase is an enzyme produced by certain strains of staphylococci which converts fibrinogen to fibrin.
Staphylococcus aureus (including MRSA) test POSITIVE.
Commensal staphylococci on skin test negative.
A positive tests is visible as clumps.

23
Q

What is the problem with testing stools?

A

A stool is a non-sterile site.

Unlike sterile sites such as blood and CSF, non-sterile sites physiologically have bacteria, making testing difficult.

24
Q

Which bacteria are routinely looked for in stool samples? How?

A

Salmonella, shigella, campylobacter and E. Coli.
Different bacteria have different culture requirements: try to kill all other bacteria and only grow the one you’re looking for.

25
Q

How is clostridium difficult detected from a stool sample?

A

Unlike other bacteria, since it is difficult to grow. Try to detect TOXINs or PCR for the toxin gene.

26
Q

How are parasites detected from stool samples?

A

Parasites are not grown but rather concentrated in the faeces and detected by staining.

27
Q

What is useful about antimicrobial susceptibility testing in bacteriology.

A

Can be used to find MINIMUM INHIBITORY CONCENTRATIONS. Typically gradient MICs.

28
Q

What is the difference between histopathology and cytopathology?

A

Histopathology looks at TISSUES, and uses biopsies, resections, frozen specimens and post-mortems.
Cytopathology looks at CELLS and uses smears and fine needle aspirates.

29
Q

In surgery, would you use a resection specimen or frozen section to rapidly diagnose whether all the cancer is out (the margins are clear)?

A

Frozen section used for rapid diagnosis. A result by telephone in 20-30 mins.

30
Q

What is often attached to antibodies in diagnostics?

A

Enzymes, fluorescent probes, magnetic beads, drugs.

31
Q

How are monoclonal antibodies produced?

A

A mouse is challenged with an antigen. Spleen cells produced antibodies and are mortal.
Myeloma cells, which are immortal, are fused with the spleen cells to form hybridomas, which both produce antibody and are immortal.
They are cultured in medium and clone by limiting dilution. Harvest the monoclonal antibodies.

32
Q

What are some uses of monoclonal antibodies?

A

Prophylactic protection against microbial infection, anti-cancer therapy, removal of T-cells from bone marrow graft, block cytokine activity.

33
Q

What department conducts hormone assays, such as T4/TSH/cortisol?

A

A subdivision of the department of chemical pathology: the department of chemical pathology (endocrinology).

34
Q

How are samples of respiratory viruses collected and then processed?

A

A nasopharyngeal aspirate (NPA) then use immunofluorescence or PCR.

35
Q

Which test tubes are used in serology?

A

Red/yellow - the clue is in the SERology. Serology is a diagnostic technique involving antibody detection in the serum (hence clot the blood and remove the clot).

36
Q

What bedside examinations of urine can you do?

A

Naked eye: clear, cloudy, haemorrhagic.
Dipstick tests: nitrites strongly suggest bacteriuria as many species of gram negative bacteria convert nitrates to nitrites.

37
Q

Why is culturing urine on agar useful?

A

Urine should be sterile so any microbial growth is potentially significant in an appropriately taken sample.

38
Q

What should you look for in faeces with the naked eye?

A

Consistency, blood, colour, presence of worms.

39
Q

Give examples in bacteriology where you directly detect antigen.

A

Meningococcal antigen in CSF,
C.difficile toxin in faeces,
Legionella and pneumococcal antigen in urine.

40
Q

What 4 criteria confer value to a screening programme?

A

The test is easy and non-invasive
There is high-uptake in the population
A significant number of cases can be detected
Something can be done about the disease.

41
Q

Give 4 problems with can happen in the cervical screening process.

A

Failure to obtain a satisfactory sample (smear),
Failure to make a proper smear,
Poor staining,
Poor interpretation.

42
Q

How are tissue samples handled?

A

Fixed on formalin (to stabilise protein bonds and prevent autolysis). Then embedded in paraffin wax.

43
Q

Give 4 uses of frozen sections.

A

Organ identification, to check the margins of an excision are clear, check lymph node involvement, check if a lump is a tumour.

44
Q

What are the purposes of the autopsy?

A

To determine cause of death, was the diagnosis correct?
Explain why treatment was unsuccessful, was it successful but did it cause complications?
Show spread of disease, where did the cancer originate?
Educate doctors

45
Q

What stain is used for most diagnoses?

A

Haematoxylin and Eosin staining.

Haematoxylin stains nuclei blue and eosin stains the cytoplasm pink.

46
Q

How are smears processed for microscopy?

A

Fixed with alcohol, stained by Papanicolaou - hence permanently preserved.

Year 2 MCD (5 decks)

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