Specimen collection and lab diagnosis Flashcards
In what stage do most lab errors occur?
the pre-analytical stage
What joint would require longer incubation?
Shoulder aspirate
What sample requires prolonged incubation for Actinomyces?
jaw infection (wound or swab)
What is the death rate percentage from errors in patient identification?
50%
How many patient identifiers do you need to confirm?
two
What are four different patient identifers?
- full name
- OHIP number
- DOB
- Hospital accession number
What kind of precautions would you take in collecting a specimen sample from a patient with MRSA or VRE?
contact precautions (in addition to routine precautions)
What kind of precautions would you take for a patient with respiratory symptoms?
Droplet precautions
In what case would you don airborne precautions whilst collecting a specimen sample from patient?
- SARs
- avian influenza
- TB
- measles
- chicken pox
- disseminated herpes zoster
What 3 types of specimens MUST be stored at room temperature?
- CSF for bacterial culture
- anaerobic organisms
- blood culture bottles
What kind of specimens MUST be stored between 2-8’C?
specimens for viral detection
What is the maximum amount of time a specimen being tested for a bacterial culture can be stored?
less than 24 hours
What organisms are negatively impacted from a delay in transport to lab?
- Group A strep from throat swabs
- N. gonorrhoeae (cervical culture)
- N. meningitidis (CSF, blood culture)
- anaerobes
viruses stable for about _ days in 2-8’C
2-3 days
Besides CSF specimens, what are some more examples of STAT specimens?
- tissue or wound culture is suspecting necrotizing fasciitis
- malaria
For blood culture, on average, how much blood do you collect?
8-10 ml per bottle
If there is a medical emergency, how much blood is taken for culture?
2 or more samples taken from different venipuncture sites, sequentially over a short period of time (minutes)
If endocarditis is suspected, how is blood taken differently?
collection happens over a period of time to show continuous bacteremia
- at least 2 positive cultures of blood samples drawn >12 hours apart, OR
- all 3 or a majority of >4 separate cultures of blood (first and last specimen drawn 1 hour apart)
A positive blood culture can reflect contamination not infection, when does contamination occur?
during the collection phase
Laboratory calculates contamination rate by counting the number of blood cultures with:
- coagulase negative staphylococci
- viridans streptococcus
- micrococcus
- propionibacterium spp
- corynebacterium spp
- bacillus spp (common in environment, survives as spore)
When using proviodine to disinfection site where blood will be drawn, how long must you wait after wiping area?
1.5-2 minutes
When using tincture of iodine to disinfection site where blood will be drawn, how long must you wait after wiping area?
30 seconds
When using chlorhexidine to disinfection site where blood will be drawn, how long must you wait after wiping area?
30 seconds
T/F: you do not need to disinfect the rubber septum of bottle because it is protected by cap
FALSE: not protected by cap MUST disinfect
Why is it uncommon to draw blood from catheter?
Because there is an increase in false positive cultures
When is it appropriate to draw blood culture from a line?
When there is a suspected line-related infection or if very difficult to draw
What does the continuous detection system look for in blood culture resulting in alarm sounds when detected?
increase in CO2 or decrease in O2
What can be concluded from a positive gram stain?
the bacteria stains purple and it is gram-positive because the walls are thick it holds onto the color of the stain
What type of bacteria soaks up the safranin stain?
gram-negative bacteria because of it’s thin walls
Which identification system detects yeast and bacteria?
Vitek2
What is the novel method for rapid identification (20 min) of microorganisms with laser pulses generating unique patterns for different types of microorganisms?
MALDI-TOF
What are four non-invasive ways to collect a urine sample?
- clean-catch midstream specimens
- catheter
- ileal conduit
- bagged specimens in pediatrics
What are four invasive ways to collect a urine sample?
- cystoscopic
- ureteral
- percutaneous nephrostomy
- supra-pubic aspirate
When collecting urine sample from foley catheter what 2 things do you NEVER want to do?
- obtain sample from the catheter bag (highly contaminated)
2. never send the tip of the foley catheter
For a wound culture what is the best type of specimen to collect?
either a tissue or fluid NOT swab when possible
What drugs are CPEs resistant to?
almost all antibiotics including, all penicillins, cephalosporins, carbapenems, etc
What are some detection methods of CPE?
- screen for resistance using susceptibility testing methods
- if MIC to ertapenem or meropenem is elevated, perform additional testing
- immunoassay
What are some bacterial causes of infectious diarrhea?
salmonella, shigella, campylobacter, yersinia enterocolitica, shiga-toxin producing E. coli, C diff
What is the most common cause of diarrhea developed in the hospital?
clostridium difficile
What are some common viral causes of diarrhea?
noravirus, adenovirus, astrovirus, enterovirus
What are some parasites that cause diarrhea?
giardia, entamoeba histolytica/ dispar, dientamoeba fragilis, tapeworms, nematodes, cryptosporidium, cyclospora
In what case would we send a rectal swab as a stool specimen?
for infants, other than that avoid sending rectal swab
If you need to collect a stool sample but the client is unable to void, can you instruct them to use laxatives?
NO do not use laxatives
When would a sample of stool be rejected for C diff?
formed stool or patient <1 year
What is a frequent error that results in rejection of stool sample?
incorrect media transport
What are some examples of irretrievable specimens?
CSF, pleural fluid, joint aspirate, pericardial fluid, vitreous fluid
What is the order of tube collection?
Tube 1: cell count
Tube 2: chemistry (glucose and proteins)
Tube 3: microbiology (need large volumes if fungal or TB cultures requested 10 ml)
Tube 4: cell count
How soon is the gram stain reported back from the lab?
within 1 hour
For CSF, what are the most common bacterial pathogens?
S. pneumoniae, N. meningitidis, Haemophilus influenzae, listeria monocytogenes, Group B strep, E. coli
Why is there a minimum of two blood samples taken?
one aerobic and one anaerobic
What infection control measures must be taken for someone suspected of meningitidis?
droplet
What is the sensitivity of cytospun gram stain of CSF?
56-86%
What is the method of detection for respiratory specimens?
Nasopharyngeal swabs (NPS)
What is the most commonly used method of respiratory viral detection?
molecular assays
What causes acute pharyngitis?
S. pyogenes (Group A streptococcus)
When collecting a sputum sample, when should the patient rinse their mouth?
First and then cough into container
Mould detection require longer incubation around 3-6 weeks, and is mainly identified based on:
- microscopy
- colonial features
- growth at different temperatures
- some reagents
- aspergillus
In fungal detection methods, what is used to diagnosis acute or chronic infection?
serology
What is the most common immunoassay method that is able to detect HIV antibody?
Enzyme immunoassay (EIA)
What diagnostic method can be used for viruses, bacteria, parasitology and fungi?
molecular methods; nucleic acid is extracted from the specimen or isolate, different methods can be used to amplify the RNA or DNA
What diagnostic method has increased sensitivity that t can detect organisms that have been delayed in transit, or cannot be cultured?
molecular method
