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

