sampling and submission of lab samples Flashcards
what are laboratory diagnostics?
a set of physical, chemical, toxicological, microscopic, pathanatomical, bacteriological, virological, mycological, hematological, biochemical, immunological, parasitological and molecular tests
samples can come from
live animals - sick or healthy
dead animals
from animal environment - living or non living
5 main laboratory groups
- microbiological - bacteriological, virological and mycological
- serological
- pathohistological
- blood assay - whole blood and biochemistry
- chemical-toxicological
microbiological tests include
bacteriological, virological, mycological
general principles on sample collection
-take samples ASAP (especially for viral or enteric bacteria)
- collect samples form in contact animals too
- collect specimens as aseptically as possible
how much blood for serology
at least 5ml
how much tissue sample
approximately 2cm3
what to put on the form for the lab
- name and address, protocol number and date
- name, surname, address and number of owner
- data on animal - species, sex, breed, age, signs, name, microchip number etc
- list of materials sent and date of sampling
- type fo lab assay
- clinical diagnosis - disease suspicion, possible pathological and morphological charges
- epizootiological data and data on treatment - drugs, duration
- name, surname and signature of person who sent material
best lab test for bacterial infection
direct microscopic exam of exudate
can get info on number, morphological characteristics and gram staining properties of microorganisms and host cellular response
specimen collection for bacterial infection
- collect from actual site of infection with minimum contamination
- transport to lab without contamination or change in relative number of bacteria
- if biopsy or FNA, skin decontamination does before
- collect aș early as possible in disease process
- get specimen before atb given if possible
swab should never be submitted from
currettings, biopsy material, fluid (esp urine) or surgically removed tissue
how to transport swabs
in a transport medium or in humidified transporting chamber
because bacteria susceptible to desiccation during transport
transporting anaerobes
need special transport devices to prevent exposure to lethal concentration of oxygen
when should blood be taken
first blood culture specimen taken at onset of fever
or take 3-4 cultures within 1-3h - if more than one culture yields the same organism it is probably significant
when would you consider contamination of mid stream voided urine
when less than 10 5 cfg/ml are isolated
best way to sample urine
cystocentesis
when to collect urine by catheterisation
when it will be performed for diagnostic or therapeutic reasons anyway
how to store urine sample
in sterile capped syringe or capped container/tube
if not cultured within 1-2h, must be in fridge for max 8h
how to collect transudate/exudate samples
sterile needle and syringe
antiseptic prep of skin
specimen put in anaerobic transport device
if a wash is used - can’t contain any bacteriostatic preservative
buffered solution eg lactated ringers solution is best as isotonic saline can be acidic
collection of faeces
2-3g preferred amount
in clean, sealed, leak proof containers
tissue sample collection
abscess sample should contain pus and abscess wall
should be placed (unfixed and without preservative) in sealed, leak proof and sterile container
in fridge if delay to lab
consideration when taking samples from necropsy
take samples for microbiology first as excessive tissue sampling and exposure can cause additional contamination
what does susceptibility tests measure
lowest concentration of antimicrobial required to macroscopically inhibit the growth of the microorganism
MIC - minimum inhibitory concentration
samples for viral disease transport
refrigerate if short term shipment 12-48h
if long term shipment, sample should be frozen and shipped don wet ice
tissues for histopathology and IHC should be fixed in buffered formalin
5 techniques for diagnosis of viral infection
- virus isolation in cell culture
- electron microscopy
- specific viral antigen detection by immunologic methods (ELISA, fluorescent antibody, IHC)
- nucleic acid detection (PCR and in situ hybridisation)
- serologic testing for specific viral antibodies
what does ELISA look for
viral antigen
what does PCR look for
nucleic acid detection
sample examples for fungal infections
from active site of infection
systemic mycoses usually from resp tract so lung tissue or airway exudate
if disseminated infection - maybe urine or bone marrow
non systemic specimens - nasal sinus, abscess, cornea, catheter, hair and nail
sample collection for dermatophyte culture
clean lesion with 70% alcohol - not iodine as harmful to dermatophytes
scape on edge of lesion or pluck hair from edge of lesion
keep at room temp - fridge is damaging
how to collect nails
by clipping
can scrape away heavily keratinised structures to access deeper portions and disinfect claw surface with alcohol
how to sample open skin lesions
without disinfection or cleaning as it may remove or kill the organism of interest
specifics about samples for fungal isolation
swabs are of limited value
swabs of cotton avoided - can be mistaken for hyphae
transport at room temp and processed asap of within 2h
urine can be put in fridge
most yeast will multiply in urine kept at room temp
what is serological reaction
isolation and identifying the causative agent, or demonstrating antibodies or antigens in tested blood serum
why are serological methods good
more reliable for latent and chronic infections than isolation of causative agent
quicker for viral diagnosis
verify immune status of the animal
when are antibodies detectable in blood titre
7th day post infection
If both samples show equal titre of antibodies it means
they are antibodies that have remained from a previous infection (residual antibody titre)
how much blood for serological testing
10ml to get 5ml of serum
how is blood collected for serological testing
in sterile tube
where to take blood from pig
cranial vena cava
jugular
ear vessels
where to take blood from poultry
wing vein - v. ulnaris
where to take blood dogs and cat s
cephalic vein - front leg
medial/lateral saphenous vein - hind leg
femoral vein - hind leg
samples for chemical toxicological testing from live animals
10ml full blood
50ml+ urine
faeces
vomit
milk sample
samples form chemical toxicology from dead animals
small animal - send whole animal
large animal - 5-10ml blood and serum asap after death and 250-300g of parenchymal organs (kidney, liver, spleen, lungs, brain)
silage samples for toxicology
3-5kg
grain or fodder sample for toxicology
1kg
water samples for toxicology
can be frozen but must not melt before they get to lab
what is transport medium
has no nutritional value and does not allow for the multiplication of the pathogen but by using it we ensure the survival of the microorganism while we are taking materials until it is inoculated on to a nutrition medium in the lab
how to take sample for CEM
taylorella equingenitalis is sensitive to metabolites of the bacteria present in sample and to presence of oxygen
needs a transport medium with added charcoal
organ samples
sent in entire pieces or as large as possible
before inoculating on culture medium, sterilise surface to prevent the growth of contamination bacteria from outer surface
interpreting results
is sample was aseptically collected with a low possibility of contamination then even small numbers of bacteria may be significant
if high chance of contamination results interpreted based on purity of the bacteriologic culture and the and quantity go bacteria isolated
how to get enteritis pathogens
faeces physiologically contain a large number of species
Salmonella, Campylobacter, Clostridium etc need specific conditions for isolation - microaerophilic/anaerobid or selective culture medium
aspergillosis interpretation
if one or more colonies of Aspergillus grow on plate - have to be interpreted with clinical picture
repeat sample if necessary
Aspergillus is normally found in environment (contamination) and can also be taken from nasal passages of healthy animals
has animal been treated - take samples at least 5 days after last therapy, incubation will take longer or be negative if still on therapy
organ/tissue for pathohistology
cut tissue in 2 parallel incisions vertically along the surface of the organ (sugar cube shape)
place in sterile container with 10% formalin - 10x greater than volume of excised tissue
what is a poison
any chemical substance or combination of chemical substances which can disturb the function of cells, tissue, organ systems and cause death of an organism
what is a toxin
a chemical substance synthesised by a living organism - Clostridium tetani, Clostridium botulinum, E.coli etc which is poisonous for another organism
