Laboratory Diagnosis Of Infections Flashcards
Role of lab in detection of infections diseases
1 detection of infectious microbes
2 anti microbes testing
3 provide timely and good quality results
4 provide advice on appropriate specimen collection
5 detection of outbreaks
6 detect possible bioterrorism events
7 infection prevention and control
Expectations from the lab in lab diagnosis
1 timely and good quality results 2 ongoing validation of tests 3 quality control of all tests 4 information dissemination 5 initial verification of all tests
Expectations of clinician in lab diagnosis
- give as much detail as possible on request form
- order and collect appropriate requests
- understand lab procedures ( working hours , limitations , abilities and rejection policies )
Describe the lab workflow cycle And list briefly what occurs at each cycle
- pre analytical phase : what are the signs and symptoms present which may be an infection aids in test selection (test selection , specimen collection and transport )
- analytical phase - numerous tests done to determine infectious disease present ( microscopy , culture methods , non culture methods , susceptibility testing )
- post analytical phase ( test review , report and dissemination )
Pearls of wisdom in test selection
- garbage in = garage out ( poor specimen gives poor quality tests )
- literature ( knowledge of disease processes and characteristics )
- available tests
- course of disease
Anatomical sites to collect samples
Which Samples are superior
- skin ( scalpel ) , sputum , saliva , skin swab , spinal tab , nasopharyngeal region , urine , feaces
- fluid and tissue samples are superior to swabs
Basic principles in sample collection
- wear ppe
- deliver sample within reasonable time range ( avoids overgrowths which contaminate )
- use leak proof containers
- submit adequate volumes where possible
- label containers accurately
- ideally collects samples before giving antibiotics as this skews results
Collecting blood sample procedure and rules
- draw blood when temp rising
- septic techniques ( ensure skin is sterile before and after )
- 2 cultures 40-60 Mins apart and diff locations and about 10-15 ml blood
- don’t draw form IV catheters
How to collect urine , procedure and rules
- clean area around urethra
- start midstream and fill 5-10 ml of leak proof container
- label accurately
- clearly explain procedure to patient
- take specimen to lab quickly
How to collect stool , procedures and rules
- use pan bed or collection bin
- only an inch collected using sterile tongue blade
- place specimen in sterile container and keep free from urine
How to collect sputum , procedures and rules
- collect 1st thing in the morning for TB tests
- try not to contaminate with saliva and sinuses fluids
4 important data needed on request forms
- type of specimen submitted ( helps know what test to undergo )
- anatomical site of specimen collection ( gives insight on microbes found there )
- method of specimen collection
- specific pathogens being sought ( aids to optimize culture conditions )
List 6 rejection criteria
- leaking container
- mismatch information
- unlabelled container
- improper specimen collection technique
- improper test requested for specimen collected
- delayed transport time
2 categories of detecting infectious disease
1 culture methods
2 non culture methods
List culture methods and give examples
1 microscopy( to seek out defining features of microbes ) - fluorescent , dark field microscopy , light , stains
2 culture ( replicates microbes natural environment to amplify it and isolate ) - selective , differential , chromogenic
List non culture methods and give examples
1 serology - co agglutination reactions , precipitation reactions
2 molecular - PCR , DNA sequencing
2 methods of microbe identification and when is it done
Describe what is AST ( briefly and give examples)
- Manual , automatic
- antimicrobial susceptibility testing ( testing response and effectiveness of therapies of a anti microbial )
- agar dilution , microbroth dilution , gradient dilution , disk diffusion
What is the light source of dark field and fluorescent microscope
When is dark field used
- radiation of the electromagnetic spectrum of diff wavelength compared to light
- when microbe isn’t easily cultured
Reasons for doing microscopy
1 to validate quality of microbe which aids in culture technique selection
2 determine if cultured organism is contaminate or pathogenic
3 guide treatment decisions by aiding in identification of microbe
3 ways to identify microbes
1 biochemical reactions
2 molecules assays
3 antisera agglutinations
Describe API index , how it works and Advantages
- analytical profile index ( for identification)
- rapid identification of bacteria
- has panels with microtubule with dehydrated substrates that are metabolized by bacterial suspension
- biochemical profile determined by color change and colors converted into numerical code wc is read from index and microbe identified
Describe the VITEK machine how it works and advantages
- miniature microbroth
- used to identify and AST automatically
- has advanced calorimetric tech to determine individual biochemical reactions of a microbes in cards
- rapid testing
- real time
- cost effective
Describe MALDI TOF MS machine , function , how it works
- automated identification machine , AST and sub-typing
- protein based
- place sample on sample plate and matrix over it
- ion of organism are excited by electrons from machine and these ions are accelerated to a spectrophotometry and read by a computer to identify a microbe
Function of serology test , when used and examples
And what is detected in the test
-to monitor infections and effectiveness of therapies
- when Pathogens are difficult to grow
- to assess immune status
- diagnose active infections ( see a specific IG or antigen and confirm )
- precipitation reactions
- co agglutination reactions
- antigens , small particles presented by APC to induce immune response
- antigens ( bodies response to pathogens )
