Clinical pathology

Question 1

What is clinical pathology

Answer 1

Development, application & interpretation of laboratory procedures for:
- establishing diagnosis &/or prognosis
- monitoring of treatment in sick animals
- monitoring animal health

Question 2

What is the purpose of clinical pathology analysis in healthy animals?

Answer 2

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)

Question 3

What tests does clinical pathology involve?

Answer 3

Haematology
Clinical Biochemistry
Cytology

Question 4

What fluids can be used in clinical pathology?

Answer 4

blood (blood, serum, plasma)
urine
fine needle aspirates (FNAs)
effusions
cerebrospinal fluid
lavages (e.g., BAL)
synovial fluid

Question 5

What anticoagulant blood tubes are there and what are they used for?

Answer 5

Haematology:
- EDTA

Clinical Chemistry:
- Serum or
- (Li-heparin) plasma
- EDTA plasma

Glucose:
- Fluoride-oxalate

Haemostasis/Coagulation:
- Citrate

Question 6

What type of blood tube should be used for measuring Ca2+?

Answer 6

Heparinised plasma

No other anticoagulants as they cause Ca+ levels to decrease

Question 7

What factors should be considered when deciding in what order to fill blood tubes?

Answer 7

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

Question 8

Label these plasma colours in cattle

Answer 8

Question 9

label these plasma colours in dogs

Answer 9

Question 10

How can you prevent haemolysis in blood samples?

Answer 10

Choose appropriate gauge needle

Never dispense blood sample through needle

Question 11

What are the effects of haemolysis in blood samples?

Answer 11

Increases in plasma/serum values of some compounds/enzymes due to higher concentration in RBC

Interferes determinations by colorimetry or interference in chemical interactions

Question 12

How can lipaemia risk be decreased when taking blood samples?

Answer 12

Fast patients appropriately

Question 13

What are the effects of lipaemia on blood samples?

Answer 13

Increases or decreases values of some compounds in plasma/serum due to:
- presence of extra lipid fractions
- turbidity caused by lipids interfering in light detection methods (colorimetry)

Main changes:
- increase in total lipid, triglycerides & cholesterol
- many determinations can’t be carried out or results significantly affected

Question 14

What are some pre-analytical sources of variation/errors in lab results?

Answer 14

patient prep

sample prep (e.g. choice of collection tube)

shipping

Question 15

What are some analytical sources of variation/errors in lab results?

Answer 15

Appropriate equipments/reagents

Quality control (e.g., equipment working?)

Question 16

What are some post-analytical sources of variation/errors in lab results?

Answer 16

Results go to wrong place or labelled as wrong patient

Inappropriate interpretation

Diagnostic sensitivity & specificity

Question 17

How can you control analytical variation?

Answer 17

validation of techniques used (assay parameters, machine setup, analytical range)
- must be known before analysis starts

Quality control
- performed regularly before/during routine analysis

Question 18

What factors affect validity of an analytical technique

Answer 18

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

Question 19

Label precision & accuracy

Answer 19

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

Question 20

Define precision

Answer 20

ability of technique to give same result for repeated measurements of same specimen with same technique

Question 21

What is the purpose of quality control (QC) in laboratory analysis?

Answer 21

Quality control ensures that analytical process is working correctly by using control materials of known composition

Helps verify accuracy & reliability of results

Question 22

What are the two types of quality control (QC)?

Answer 22

Internal QC → Uses patient samples for monitoring accuracy

External QC (EQA) → Involves external comparisons but is not contemporaneous