CP3-3 infection tests Flashcards
What are the main test used in the diagnosis and management of infections?
Blood tests for FBC, inflammatory markers, lactate, LFTs, Urea and electrolytes (U&Es)
Serology
PCR tests
Microscopy, culture and sensitivity testing
Chest and bone X-ray, CT, FDG-PET/CT scans
What are three inflammatory markers tested for in blood tests?
CRP (c-reactive protein)
ESR
Procalactinonin
How is white blood cell count affected by bacterial infection?
Raised
How is white blood cell count affected by viral infections (apart from covid)?
Normal
How is white blood cell count affected by Covid-19?
Decrease
How is lymphocytes count affected by bacterial infection?
Normal or low
How is lymphocyte count affected by viral infection (apart from Covid-19)?
Raised
How is lymphocyte count affected by Covid-19 infection?
Decreased
How is neutrophil count affected by bacterial infection?
Raised
How is neutrophil count affected by viral (apart from Covid-19) infection?
Normal
How is neutrophil count affected by Covid-19?
increased
What part of the immune system are inflammatory markers?
Innate immune system
How do the results of inflammatory marker tests affect the diagnosis of infection being made?
Raised = support diagnosis
Negative = infection less likely
Fill in the blank.
Culturing of the infection-causing pathogen needs to be done _________ antibiotics are started.
Before
What is the process of blood culture sampling?
- Obtain sample from patient using aseptic technique
- Safely and correctly label the sample
- Transport sample to the lab using appropriate storage if required
- Incubate at 35-37C for 5-7 days and monitor CO2 to detect any microbial growth.
- A gram film of the blood culture medium is taken, examined and reported immediately to clinician
- Further incubation of some of the medium on a range of culture media.
- preliminary susceptibility testing may be carried out at this point .
- Results of this testing are communicated to the clinician
- Overnight incubation for definitive identification of organisms and additional susceptibility testing
- A final summary is released after all testing is complete.
What is TTP?
Time to positivity - the time it takes for growth to be detected in a blood culture
How long is TTP usually in significant bacterieamia?
When may it be shorter?
When may it be longer?
12-24 hours
Shorter if overwhelming sepsis
Longer if fastidious organisms like brucella species
What temperature is classed as a fever?
> 38.0 C
What can CT scans be combined with to support infection diagnosis?
PET scans
What are two tests that can help identify severe sepsis and respiratory failure?
Blood lactate
Blood gases
What is the basic process of sensitivity testing?
A microorganism is cultured in the presence of antimicrobial agents to work out if the concentration of antimicrobial safe to put in the body is high enough to kill the microorganism
Why is sensitivity testing used?
To inform decisions on target antimicrobial therapy
What type of therapy is used in the initial treatment of an infection? What about subsequent treatment?
Empiric therapy.
Targeted therapy requiring isolation of the microorganism and antimicrobial susceptibility testing.
What can direct detection of microorganisms detect?
The whole organisms via microscopy
Components of the organism like antigens or nucleic acid (DNA or RNA)
What is an example of an antigen that can be detected during a detection test at the bedside?
Legionella antigen
What is involved in antibody detection?
IgM detection
Seroconversion
Fourfold rise in titre
What is an example of immunological testing (apart from antibody testing)? What is this test often used to diagnose/exclude?
IFN-y release assays
TB
What is an example of a test used in detection of bacterial nucleic acids in infections?
16S PCR
How do immunological tests work?
By detecting whether the body is undergoing an immune response to an infection
Which three processes does microbiological diagnosis rely on?
Direct detection
Culture
Immunological testing
