Clinical biochemistry - intro Flashcards
What 4 steps must be carried out before taking bloods?
- take the history
- perform a physical examination
- identify clinical problems
- formulate a differential diagnoses
What steps are taken following a differential diagnosis?
- Tests to narrow down the list of possible diagnosis
- Identify profile or pattern of changes
- May need further specialist tests
- Diagnosis
- Treatment
Give some examples of screening tests
- Urine sample
- Radiography
- Ultrasound
- Biochemistry panel
- Haematology
Define the term clinical biochemistry
The analysis of samples of body fluids for the purpose of diagnosis, treatment and prevention of disease
Which body fluids are most commonly used for analysis?
Serum
Plasma
Urine
What must be added to a plasma sample and why?
Anticoagulant to avoid clotting
What does plasma contain?
Proteins - albumin, globulin
Electrolytes
Water
What must be done to a serum sample?
Must be left and allowed to clot
Out of serum and plasma, which does not contain coagulation factors?
Serum
What are the functions of plasma?
Transport to and from tissues: - Nutrients - Hormones - Metabolites and vitamins Blood clotting Maintenance of osmolarity
What must plasma samples harvested from blood be kept in?
Lithium heparin tubes (anti-coagulant)
Plasma obtained from blood is placed in what kind of tube for a coagulation sample?
Sodium citrate - prevents the action of coagulation factors
What are the 3 waste products of plsama?
- creatinine
- urea
- bilirubin
What tube must blood be placed in for a serum sample?
A glass tube
How is serum collected?
- place blood in a glass tube
- allow blood to clot
- centrifuge and separate supernatant
What is an alternative serum collecting method?
Plastic tubes with a serum activator and separation gel can be used - allows better separation from clot and cells
If being sent to a lab plasma/serum should be collected into what type of tube?
NaFlouride/oxalate or EDTA tube = grey top
What would you run tests for to assess kidney function?
Creatinine
Urea
Phosphate
USG
What are the effects of decreased serum conc?
Decreased input: - Decreased synthesis - Nutritional deficiency - Poor absorption Increased output: - Excessive demand - Increased excretion
What are the effects of increased serum conc?
Increased input: - Increased synthesis - Tissue damage and leakage from intracellular compartment Decreased output: - Decreased utilisation - Impaired excretion
Where are reference interval values from?
The median 95% of a tested population of healthy animals
What is standard devaition?
The spread of values around the mean
How are normal and pathological ranges spread:
- ideally
- in reality
- Ideally their ranges would be separated
- In reality there is often overlap providing a ‘grey area’
What is the risk that comes with ‘over testing’
If many tests are performed on an individual animal the likelihood that a test result will come back as abnormal increases
Give some pre-analytical error examples
Sample collection, handling, submission
Technique
Tubes
Timing
What are preanalytical errors caused by?
- Sample labelling and transcription errors
- Inadequate anticoagulant
- Sample contamination
- Improper handling
- Long or inappropriate storage
Give some examples of analytical errors
Due to test methodology
- Not calibrated
- Interfering substance
- Test method performance
What are possible sources of analytical errors
- incorrect reporting of results
- failure to calibrate refractometer
- contamination of serum with EDTA
- delayed separation of plasma/serum
Compare the definitions of accuracy and precision
Accuracy = how close the test result is to the 'true value' of the analyte Precision = the reproducibility of a laboratory method
Define the definitions of sensitivity and specificity
Sensitivity = the likelihood of a positive result when disease is present Specificity = the likelihood of a negative result when the disease is absent
Screening test must be very …
Confirmatory tests must be very …
Sensitive as you do not want to miss any infected animals
Specific as we want to be sure than the positive animal really has the disease
Give definitions of positive and negative predictive values
PPV = the likelihood that a patient with a positive result has the disease NPV = the likelihood that a patient with a negative test does not has the disease
Which 3 factors affect PPV and NPV?
Specificity
Sensitivity
Prevalence of disease
