Diagnostics Flashcards
What do the different coloured caps represent on blood sample tubes?
o RED top = no anticoagulant
o YELLOW top = have gel to speed up clot
o PURPLE top = have potassium EDTA
o GREY top = have fluoride oxalate (poison)
Why would you want potassium EDTA in the sample tube?
- keep the cells alive -> for test involving RBCs, WBCs or platelets
Why would you want fluoride oxalate in the sample tube?
- a poison that kills RBCs -> used to measure blood glucose -> if RBCs are alive they will consume the glucose
What colour capped tube is used for U&E?
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- serum in yellow or red
What colour capped tube is used for glucose?
- plasma in grey
What colour capped tube is used for HBA1c?
- plasma in purple
What colour capped tube is used for TFT?
- serum in yellow or red
- any hormone goes in a yellow or red top
What colour capped tube is used for liver function tests?
- yellow or red top
What is a blue top container used for?
- contains citrate -> an anticoagulant
- used to measure clotting factors
- is reversible which makes it useful
When do you need to contact a chemical pathologist?
- want the sample to be rapidly centrifuged out of hours
- want to measure labile hormones such as insulin
- urgently need CSF glucose and protein to be measured -> meningitis (or another bacteria then they will consume the glucose) and as lumbar puncture is usually only done when a patient is very ill
What is a maculopapular rash and name one disease associated wih it?
- some raised areas and some flat covering the entire body
- measles
Define a dermatomal rash and name a disease in which it is featured.
- a rash confined to a few dermatomes
- shingles
What can be detected in a virology lab?
- Infectious Virus -> virus isolation and electron microscopy
- Protein Components (antigens) on the virus -> e.g. p24 antigen in HIV, surface antigen in HBV etc.
- Genetic Components of the virus (DNA or RNA)
- Host Response -> antibody or cell responses
Define sensitivity.
- the test’s ability to correctly identify positive samples
Define specificity.
- the test’s ability to correctly identify negative samples
Which antibody is a marker of recent infection?
- IgM
- IgG comes later on
What samples are typically sent off for virology testing?
What are the 4 main diagnostic techniques used in bacteriology labs?
- culture
- serology
- molecular techniques
- anti-microbial suspectibility testing
Name the main use of cultures.
- work out what antibiotic to use
What are the major problems with cultures?
- takes about 24 hours to grow the bacteria and another 24 hours to do the susceptibility testing
- good in sterile sites (CSF, blood etc), because there should NOT be any bacteria so an grows is abnormal -> however in non-sterile sites (skin or gut), there are loads of bacteria that could have colonised but may not be causing any problems
When is serology used?
- to check the bodies response to infection
- if the organism can’t be cultured -> syphilis
Why are molecular techniques not commonly used?
- rapid and sensitive but there is a range of resistance genes
- is good for MRSA as the encoded resistence is in the MecA gene
Which of the four main bacteriology tests is the most useful to doctors in general?
- antimicrobial suspectibility testing -> checks to see if antibiotics are effective on the bacteria
Describe the process leading to a positive blood culture diagnosis.
- blood is added to broth inside bottles that has nutrients for the bacteria and then it is incubated (around 37 degrees)
- there is an indicator at the bottom of the tub, the waste products of the bacteria will cause a change in colour of the indicator at the bottom -> is effectively a glorified pH detector
- this process take around 18-24 hours
What happens after a positive blood culture result occurs?
- a confirmation of whether the blood cultures are positive or negative
- generally: -ve = skin and soft tissue +ve = abdomen and urinary tract
If possible, at what point should blood cultures be sent?
- before administration of antibiotics -> with most bacteria there is a small window where you can test the cultures before giving antibiotics
- ANTIBIOTICS IMMEDIATELY GIVEN IN PATIENTS WITH MENINGITIS OR MENINGOCOCCAL SEPTICAEMIA
What is the point of the staphylococci coagulase test?
- to distinguish between coagulase positive and staphylococci
o Coagulase POSITIVE = STAPHYLOCOCCUS AUREUS (the most important of coagulase positive staphylococci) -> coagulase is a virulence factor which helps Staphylococcus aureus to cause infection
o Coagulase NEGATIVE = common skin microbes -> don’t tend to cause infection unless there are some opportunistic circumstances (e.g. central lines, prosthetic joints)
What are possible causes of diarrhoea?
o bacteria: common -> Salmonella (including S. typhi), Shigella, Campylobacter
uncommon -> E.Coli, C. difficile, Cholera
o parasites: Amoeba, Giardia, Cryptospordium (uncommon)
o viruses: generally associated with acute symptoms
What 3 bacteria are commonly screeened in stool samples?
o Salmonella
o Shigella
o Campylobacter
- any others have to be requested specifically
Define Minimum Inhibitory Concentration (MIC).
- the lowest amount of antibiotic required to inhibit the growth of bacteria in vitro
When is a bacteria reported as being resistant?
- if the MIC is above the breakpoint from the guidelines
- breakpoint is the point in which the concentration is not going to be clinical possible
What is the role of histopathologists?
o interested in tissues
- biopsies
- resection specimens
- frozen sections -> when the patient is in surgery and an answer is needed
- post-mortems
What is the role of cytopathologists?
o interested in cells
- smears -> cervical smears fro cancer is the most common
- fine needle aspirates
How are section obtained?
- specimens are recieved -> must be properly labelled
- fixed in formalin
- embedded in paraffin wax and sections are cut
What tests are carried out on sections in histopathology?
- stained
- identification of specific antigens -> immunohistochemistry
- molecular tests
- microscopy
Which part of antibodies are variable and constant?
- constant = Fc
- variable = Fab
What can be conjugated to antibodies in labs/for treatment?
- enzymes
- fluorescent probes
- magnetic beads -> purification of cell types
- drugs -> target particular tumours
How are monoclonal antibodies produced?
- normal B lymphocyte, are taken from the spleen, which is producing the antibody of interest and you FUSE IT with a myeloma cell line -> gives you a HYBRIDOMA
- these cells have the ability to produce the antibody of interest -> as it is fused with a tumour cell, it can divide indefinitely to produce great numbers of thje antibodies
What are the therapeutic uses of manufactured antibodies?
- prophylactic protection against microbial infection
- anti-cancer therapy
- removal of T-cells from bone marrow grafts
- block cytokine activity
What are the diagnostic uses of manufactured antibodies?
- tissue typing
- blood group serology
- immunoassays -> hormones, antibodies, antigens
- immunodiagnosis -> infectious disease, autoimmunity, allergy, malignancy
Where is immune complexes the biggest problem?
- kidney function
If immunodeficiency is suspected clinical, what tests would ran in an immunology lab?
- serum immunoglobulin levels - serum electrophoresis, ELISA
- specific antibodies - protein antigens or polysaccharides antigens
- lymphocyte subsets
Describe the natural history of HIV infection.
- someone who hasn’t had HIV treatment
o BLUE - CD4 T cell count
o RED - viral load
- primary infection - CD4 will initially go down and then it will go up again after a few weeks
- viral remains controlled by the immune system for some time (clinical latency) -> viral load wont change that much during this time but CD4 will keep going down
- when the CD4 count gets very low, the patient will start showing signs of opportunistic infection -> CD4 count continues to go down, the viral load will go up
- a patient that has been diagnosed with HIV, you would monitor their CD4 count and measure their viral load
- once their CD4 reaches a certain level you would start antiretroviral therapy
What disease appear when CD4 starts to drop in HIV?
Name a pneumonia only seen in immunocompromised.
- Pneumocystic pneumonia
