clinical pathology Flashcards
SPECIALTY TRAINING IN LABORATORY MEDICINE
Anatomical Pathology General Pathology Hematological Pathology Medical Biochemistry Medical Microbiology Neuropathology
Precision
Precision: the values obtained on repetitive measurements
- is usually reported as standard deviation
Precision reflects:
the reproducibility of a given analysis or
how well the analysis is done when repeated many times
In general:
if the analyses are done very carefully, the precision will be high
if the analyses are done carelessly, the precision will be low
- Reproducibility of Replicate Analyses
Accuracy
the extent to which measurements approach the “true” value.
Accuracy - Relationship of Result obtained to Correct or “True” Value
subjective
what the client says
objective
what is found after examination
high level of accurasy and high precision
right in the bullseye
low levels or accuracy and high precision
concentrated but not in the bulls eye
low accuracy and low precision
all over the place
Accuracy - Relationship of Result obtained to Correct or “True” Value
Any data collected may be arranged in the form of a Gaussian distribution
Median
the Value at the centre of all observations with ,an equal‘ number of observations preceding and following it
Range
Range is the difference between the highest and lowest observations
Causes of Variability!!!!!!!
Biologic Variability
Inter-Individual: Race Gender Age Body Size
Intra-Individual: Diurnal Variations Circadian (time of the day) Menstrual Cycle Seasonal Aging
Analytic Variability:
Inaccuracy
Imprecision
Post-Analytic Variability:
Transcription Errors
Why Physicians Order Tests
first view:
- To confirm a clinical impression.
- To rule out a possible diagnosis or disease.
- To use as a therapeutic or management guide.
- To use as a prognostic guide.
- To detect disease (screen).
SECOND VIEW
- To diagnose disease.
- To screen for disease.
- To determine the severity of disease.
- To determine appropriate management of the patient.
- To monitor progress of the disease and to monitor therapy.
- To monitor drug toxicity.
- To predict response to treatment.
Screen Patient
Confirm/ Rule Out Specific Diagnosis
Follow Course of Disease (Management)
Why Physicians Order Tests
first view:
- To confirm a clinical impression.
- To rule out a possible diagnosis or disease.
- To use as a therapeutic or management guide.
- To use as a prognostic guide.
- To detect disease (screen).
SECOND VIEW
- To diagnose disease.
- To screen for disease.
- To determine the severity of disease.
- To determine appropriate management of the patient.
- To monitor progress of the disease and to monitor therapy.
- To monitor drug toxicity.
- To predict response to treatment.
Steps in Ordering - Problems
MD writes order Inappropriate Test Handwriting NOT legible Request on wrong form/Wrong Entry Wrong Patient ID 2. Clerk writes requisition Form lost or delayed Wrong addressograph plate used
Phlebotomist draws blood Wrong Patient Sample hemolyses Inadequate volume Tourniquet on too long Blood diluted with IV fluid Wrong time
Timing of Lab Tests
Most Tests are done at 8:00 am
Fixed time
Most studies are based on this time
Since many tests are fasting, most convenient time for patient.
Therapeutic Drug Monitoring:
5 hours after last dose (minimum) or
just before next dose (maximum)
Patient Preparation
1) Fasting - Overnight fast.
2) Lipids (cholesterol & triglycerides) : 12 - 16 hour fast.
3) Hormone Function Tests - usually require 2 days of baseline function before stimulation or suppression tests.
Specimen Collection, Transport & Storage
The method of collection, transport and storage of the specimen can influence the final result and thus is extremely important that one understands the factors which could influence these process.
example: the glucaose in a test can be metabolised and disapear
the speciment must —– to be biologicaly meaningful- dont need the last or few slides very well
Specimen must be representative and homogeneous to be biologically meaningful
Factors to consider before obtaining specimen (sample):
Does the test require the patient to be fasting ? (eg. Glucose)
Does the position of the patient effect the result? (eg. Recumbent or upright – effect Renin & aldosterone)
Possible drug/medication interference (eg. Allopurinol – uric acid)
Therapeutic drug monitoring & time of specimen collection in relation to drug dosage schedule (eg. Digoxin/Gentamycin)
Effect of intravenous infusion
Adequate Labelling (name, number, time, etc.)
Adequate clinical information
Time of collection of specimen (eg. Cortisol,etc
- Venipuncture technique:
know 2-3 tubes and their process
Tournique application
Hemolysis – interfere
Adequate mixing
Sufficient quantity
green top- heparin
prevents clotting in vile
lavendar top
acts be removing calcium ion by chelation but also chelates other ions in the blodd
Physician’s Role
Is the result Unreasonable, Unphysiologic or Impossible ?
Is the result consistent with the Previous Results ?
Is the result consistent with the Clinical Picture ?
Truth Table
know
++= true positive…
Definitions
sensitivity
specificity
prevelance
Sensitivity - Frequency of Correct Result in Patient with Disease
Specificity - Frequency of Correct Result in Healthy Patient
Prevalence – Frequency of Disease in Target Population/The total subjects examined who are diseased
Sensitivity understand!!!!
Sensitivity - Frequency of Correct Result in Patient with Disease
Percent positivity in disease:
Sensitivity =
tp/tp+fn ) x100
tp/ all sick subjects x100
Specificity
Frequency of Correct Result in Healthy Patient
Percent Negativity in the absence of the disease:
Specificity =
tn/ tn+fp) x100
true negative/ all subjects free of desease )x100
Truth Table Definitions
Positive (+) Predictive Value
(+)pv= tn/tn+fn ) x100
negative predictive value :
(-)= tn/tn+fn) x100
Efficiency
tn +tp/ tn+fn + tp+fp )x100
prevelance
tp+ fn/ tp+tn+ fp+ fn) x100
sensitivity: 90%
s
specificity= 96%
s
predictive value 96%
ssss
negative predictive
91%
efficiency
93%
prevelasnce
50%
