Diagnostic process Flashcards
Steps of diagnostic process
- Patient assessment
- Pre-analytical
- Analytical
- Post-analytical
Patient assessment
-Problem oriented approach
-integration of history, presentation, physical exam findings and lab data
Pre analytical
- specimens selected and collected
- Lab provided with all relevant info
- sampled shipped to lab
- Lab decides on appropriate tests
Analytical
1.Direct exam of specimens
2.Preliminary report which can be compared with patient info
3. Sample processing
4. Primary set of results (ex. culture) recorded
5.Secondary tests selected and conducted
Post-analytical
- Final lab results and report by diagnostician
2.Interpretation of report by vet
**leads back to patient assessment and DIAGNOSIS
Principles of sampling
- Obtain sample from site of infection; minimize contamination
>culture margins of abscess and collect urine by cystocentesis - Collect sample at correct time
>shedding stage of pathogen - Collect a sufficient quantity of sample
>Ask the lab what they need! - Use appropriate collection device
>sample must be sterile
>use contained designed for sampling - Handle/store sample appropriately
>can sample be frozen? Special transport media needed? - Obtain cultures before administering antibiotics
>otherwise cannot interpret a negative test
7.Make smears in addition to cultures
>can be done in house; gram stains!
- Label everything!!
- Dont put anyone in danger! Is it a zoonosis?
Most common injury during diagnostic process
Needlestick injuries
-can lead to tendon sheath infections=amputations or other infections
*dont recap needles, dispose sharps after use in sharps container,
What would lab use to detect bacteria?
culture
What would lab use to detect parasite related structures?
microscopy
What would lab use to detect DNA/RNA?
PCR
What would lab use to detect antibody or antigen?
ELISA
What would lab use to detect tissue structures?
-histological examination
What would lab use to detect differential cell counts?
Blood
What would lab need for biochemical analysis?
blood or urine
To freeze or not to freeze?
**Always check with lab
-for bacteriological/mycological culture= don’t freeze
- non-propagative tests= freezing possible
-can freeze milk
-can freeze samples to be tested for L. monocytogenes
Common labs in Western canada
- Diagnostic services in UCVM calgary
- True North Vet diagnostics- Langley; private
3.Animal Health Branch Abbotsford - Prairie Diagnostic services in Sask
- Veterinary Diagnostic Services
- IDEXX
Shipping samples safely
-shipping regulations depend on what you’re sending
-In general:
>water tight primary container
>Absorbant material
>watertight secondary container
>sturdy outer packaging
Sample processing conducted by the lab
1.Sample received
2.Sample processed in biosafety cabinet (where sample smears can be made/stained to provide preliminary report)
3. Incubation 18-24 hrs
4. Any bacteria grown identified
5. Antimicrobial susceptibility testing (AST)
6. AST incubation
7.Final report
Susceptibility testing
-conducted to determine the therapeutic guidance required for veterinarian to treat patient
**basically help determine the most appropriate antimicrobial for the issue at hand
Susceptible vs. resistant
Susceptible: high likelihood of clinical success if an organism is susceptible to drug
Resistant: clinical failure is predicted if an organism is resistant to drug
Divisions of resistance
- Intrinsic resistance
- Acquired resistance
Intrinsic resistance
-constitutive
-naturally resistant to a drug. No acquisition to the drug, but instead it is natural for the bacterial species
Acquired resistance
-not inherent to the organism
-“superbugs”; have a gene or mutation which differentiates from the wild-type making a drug that is normally used no longer effective
SPICE organisms
Serratia
Providentia
Indole positive Proteae
Citrobacter
Enterobacter
What resistance do SPICE organisms have?
They produce AmpC beta-lactamases resulting in cephalosporin resistance
Types of susceptibility test methods
1.Categorical methods- tells you whether organism is susceptible or resistant
- Quantitative methods- yields a minimum inhibitory concentration describing exactly how susceptible or resistant an organism is
Minimum inhibitory concentration
the lowest concentration of a drug inhibiting bacterial growth
*represented as a number on a doubling scale
Categorical susceptibility test example
Kirby-Bauer (disks)
Quantitative susceptibility tests
-Gradient strips (E-tests)
-Agar dilution
-Broth dilution
Interpretation of susceptibility tests
-use standardized interpretive criteria
>Will say “less than # = resistance”
What factors are used to make up interpretations for susceptibility tests?
-Definitions based on species, indication (issue), drug, dosing regimen.
Changing the typical use of a drug (adjusting any factors) will reduce the interpretation power of the susceptibility tests
Sensitivity vs. specificity
Sensitivity: Few false negatives so less cases of disease missed
Specificity: Few false positives. Ability to ensure that negative individuals are considered negative for disease
Postive vs. negative predictive value
Positive predictive value: reflects the proportion of subjects that are positive for disease who actually have the disease
Negative predictive value: reflects the proportion of subjects with negative test result who truly do not have outcome of interest/disease
