The Clinical Applications of Pathology Tests and Quality Assurance Flashcards
Where can the cost of various pathology tests be found?
Medicare Benefits Schedule Book
What is the Ulysses syndrome?
When a healthy patient receives a false positive result and has many other unnecessary follow-up investigations
What are the 4 reasons for pathology tests?
Screening
Diagnosis
Prognosis
Monitoring
What should be done if a patient’s test result is above the population median?
If mildly elevated, monitor with another test in some years’ time
If highly elevated, requires action
What would be the PPV of a test with 99% specificity and 99% sensitivity where the prevalence of disease is only 1%? What is the clinical implication of this for screening programs?
50% - there would be as many TPs as FPs
In screening programs there are almost always more FPs than TPs
What are the FPG, OGTT and HbA1c thresholds for the diagnosis of diabetes?
FPG >7.0 mmol/L
OGTT >11.1 mmol/L
HbA1c >6.5%
Describe the Rotterdam criteria for diagnosis of PCOS and how can these findings be elicited clinically
2 or more of the following: Chronic anovulation (amenorrhoea) Hyperandrogenism (hirsutism/biochemistry) Polycystic ovaries (US)
For what disease is the Gleason score used to provide an indication of prognosis?
Prostate cancer
What is serum sodium used as an indicator for?
Risk factor for in-hospital mortality (increased risk if low or high)
Explain the concept of “reversion to the mean” in monitoring
A healthy person oscillates about their set point - this is a good indicator
What is the role of tumour marker doubling time in monitoring cancer patients?
Provides an indication of expected exponential growth of tumours
What factors are important in therapeutic drug monitoring?
Absorption
Distribution
Drug half life
Peak level, trough level
What is important when measuring electrolytes besides the absolute level?
Rate of change
Overall trend
How should the y axis units be expressed when monitoring tumour markers?
On a logarithmic scale
What % of clinical decisions are based on results from the laboratory?
70-85%
What % of laboratory test errors occur at the preanalytical test stage?
68%
Give 5 examples of preanalytical error
Insufficient sample Poor sample condition Incorrect sample Incorrect identification Sample handling and transport
KIMMS
Key Incident Management Monitoring System
Where do most of these preanalytical errors occur?
Emergency
What details should be included on a pathology request slip?
At least 2 patient identifiers Urgency Dr name and contact Collection details and collector Clinical indication Signature and date
What details should be included when labelling a sample?
At least 2 patient identifiers
Day and time of collection
Collector
NB Should all match up with request slip!
What types of tubes are used to prevent coagulation of a blood or plasma sample (e.g. for an FBE, to measure clotting factors)?
K2EDTA (for FBE) EDTA Citrate Oxalate Heparin
What sample is allowed to clot? Why?
Serum
To get rid of clotting factors which can interfere with tests, e.g. immunoassays
When is acid preservative added to a urine sample?
When measuring calcium and/or catecholamines
When is alkaline preservative added to a urine sample?
When measuring uric acid
When should a urine sample be refrigerated?
For MCS
When should a spot faecal sample taken?
FOBT
When should a 3 day faeces collection be taken?
For faecal fat
Why are 3 samples taken during lumbar puncture?
Because often some initial blood contamination; first tube for chemistry, second culture, third microscopy (where it is important to analyse for RBCs in the CSF)
List 5 common errors in blood collection
Haemolysed specimen Delayed transport Inappropriate refrigeration Contamination from another tube type Drip arm specimen
What effect does haemolysis have on potassium levels?
Artificially elevates
How long does it take for a RBC sample take to consume its glucose?
3 hours; after this will haemolyse
What is the effect of refrigeration on a RBC sample?
Cells stop working within 30 mins
How is a ruptured specimen produced?
Via turbulent collection of samples through fine bore needles/taps
What is the “order of draw” for collection of blood samples?
From non-preservative containing tubes to tubes with preservatives
What is the major issue with contamination from an FBE tube?
Will cause artificially high K+ and low Ca2+; this is normally a medical emergency
If there is a drip in the wrist, what % of cubital vein blood on the same arm will be drip?
30%
What can be used to prevent glycolysis (in order of quickest to slowest effect)?
Acidity (i.e. fluoride citrate)
Serum gel tube if spun
Fluoride
