Clinical pathology Flashcards
What is clinical pathology
Development, application & interpretation of laboratory procedures for:
- establishing diagnosis &/or prognosis
- monitoring of treatment in sick animals
- monitoring animal health
What is the purpose of clinical pathology analysis in healthy animals?
Monitoring of production/performance (e.g. metabolic profile in dairy herd)
Monitoring during critical periods (e.g. for anaemia in piglets)
Special purposes (e.g. transport/export)
What tests does clinical pathology involve?
Haematology
Clinical Biochemistry
Cytology
What fluids can be used in clinical pathology?
blood (blood, serum, plasma)
urine
fine needle aspirates (FNAs)
effusions
cerebrospinal fluid
lavages (e.g., BAL)
synovial fluid
What anticoagulant blood tubes are there and what are they used for?
Haematology:
- EDTA
Clinical Chemistry:
- Serum or
- (Li-heparin) plasma
- EDTA plasma
Glucose:
- Fluoride-oxalate
Haemostasis/Coagulation:
- Citrate
What type of blood tube should be used for measuring Ca2+?
Heparinised plasma
No other anticoagulants as they cause Ca+ levels to decrease
What factors should be considered when deciding in what order to fill blood tubes?
can’t risk bacterial contamination from other tubes for blood culture
can’t delay citrate sample for coagulation because can’t risk coagulation starting before sample hits citrate
don’t want to risk contaminating our chemistry samples with EDTA
Label these plasma colours in cattle
label these plasma colours in dogs
How can you prevent haemolysis in blood samples?
Choose appropriate gauge needle
Never dispense blood sample through needle
What are the effects of haemolysis in blood samples?
Falsely increased plasma/serum values of compounds with higher RBC content:
→ e.g. K⁺ (esp. in horses), inorganic phosphate, LDH, AST
Interference in lab tests:
→ Colour interference: bilirubin overestimated (similar absorbance to Hb)
→ Chemical interference: creatinine underestimated (e.g. Jaffe method in ketosis)
How can lipaemia risk be decreased when taking blood samples?
Fast patients appropriately
What are the effects of lipaemia on blood samples?
Alters plasma/serum values (↑ or ↓) due to:
→ extra lipid fractions
→ turbidity interfering with light-based detection (e.g. colorimetry)
Main effects:
→ ↑ total lipids, triglycerides, cholesterol
→ many test results unreliable or not measurable
What are some pre-analytical sources of variation/errors in lab results?
patient prep
sample prep (e.g. choice of collection tube)
shipping
What are some analytical sources of variation/errors in lab results?
Appropriate equipments/reagents
Quality control (e.g., equipment working?)
What are some post-analytical sources of variation/errors in lab results?
Results go to wrong place or labelled as wrong patient
Inappropriate interpretation
Diagnostic sensitivity & specificity
How can you control analytical variation?
validation of techniques used (assay parameters, machine setup, analytical range)
- must be known before analysis starts
Quality control
- performed regularly before/during routine analysis
What factors affect validity of an analytical technique
Precision: repeatability/reproducibility
Accuracy: measuring right thing correctly
Specificity: ability of technique to measure single analyte in complex solution
Sensitivity & range: interval between lowest & highest concentration that technique can measure
Label precision & accuracy
Precise & accurate:
- Best situation
Precise & Inaccurate:
- allows adequate within-lab comparisons, but inter-lab comparisons are questionable
Imprecise & accurate:
- Use possible only if:
1. differences physiologic vs pathologic are wide
2. use of mean of repeated measurements to increase precision
Define precision
ability of technique to give same result for repeated measurements of same specimen with same technique
What is the purpose of quality control (QC) in laboratory analysis?
Quality control ensures that analytical process is working correctly by using control materials of known composition
Helps verify accuracy & reliability of results
What are the two types of quality control (QC)?
Internal QC → Uses patient samples for monitoring accuracy
External QC (EQA) → Involves external comparisons but is not contemporaneous
