quality assurance Flashcards
what is preanalysis stage ?
all the steps before the sample is analysed
such as ordering and sample collection
what is analysis stage ?
lab activity that gives diagnosis results
such as staining, running the sample on an analyser
what is post analysis ?
patients reporting and interpretation of the results
what are some of the pre analytical errors ?
precollection variables which is patient related :
exercise - increase in AST , CK , lactate
Diet - high after glucose ,
vegeterains - vitB12 and total lipids are low
diurinal variation - cortisol , ACTH , insulin
stress
posture - upright - increase in albumin
specimen collection and labelling
preserving the specimens , and anticoagulants
specimen transport and storage
when are specimens rejected ?
clots in anticoagulated specimen icterus , hemolysis nonfasting specimen improper blood collection wrong volume collection
what are the recommended blood collection order ?
serum tube - nothing
clot tube - sodium citrate
plasma tube - sodium heparin- biochemical reactions
EDTA tube - hematological
glucose tube - sodium fluoride / sodium heaprin
other collection tubes
what does the clot tube contain ? and what is it used for ?
sodium citrate 1:9
the clotting mechanism
what does the plasma tube contain ?
and what is it used for ?
lithium heparin / sodium heparin (anticoagulants)
plasma biochemical test and rheology measurements
what does EDTA tube contain and what is it used for ?
EDTA-K2
clinical haematology
what does the glucose tube contain ?
sodium fluoride and potassium oxalate / sodium heaprin
in preanalysis how is the specimen stored ?
open tubes are stored in room temp
not in direct sunlight or heating devices because it increases hemolysis and enzyme denaturation
serum/plasma not removed from cells increases gamma glutamate transferase by 27 percent in half an hour
creatine 110 percent increase in plasma and 60 percent in scrum
what are the collection techniques for a finger or heel puncture
infants less than 12 months - lateral or medial plantar heel surface
more than 12 months old , children, adults - palmar surface of second third and fourth finger (first and fifth - no)
should not be oedematous or previously punctured
warm the puncture site
cleanse the puncture site
dry
perpendicular to skin and puncture it
wipe away the first drop of blood
gentle pressure , but do not milk the site - hemolysis and excess tissue fluid
collect specimen in suitable container by capillary action
label specimen - with date anytime , and patient information , indicate it was a skin puncture
preanalysis techniques for arterial puncture
0.05ml liquid heparin /1ml blood for blood gas analysis
needle pierce the skin at angle 45-60 degrees , slow and deliberate.
after collection compress the puncture site quickly to expel air from the syringe -3 to 5 minutes
mix the specimen to ensure anticoagulation and place it in ice water - minimise leukocyte consumption of oxygen
what are the errors in the analytical step ?
introduction and transport to cute or dilution cup
addition of reagent
incubation errors
mixing of sample and reagent
insufficinet analytical specificity and sensitivity
incorrect calibertaion procedure
reagents
what are the errors in post analytical stage ?
wrong calculation
reporting wrong results to patient
incorrect interpretation
flags for specimen that require additional analysis with other method
assessment of clinical significance of results
such critical values
referential values
factors influencing reference range
what are the factors which influence reference range ?
different lab methods
different tubes
lab are encouraged to perform their own studies of reference ranges usually be testing 120 samples from non diseased individuals
or can use verified referee interval
what is critical value ?
lab result which is life threatening
no universe guidelines which assays should have critical values - what the threshold must be , or whether results should be repeated before reporting
what is sensitivity ?
the ability of a test to detect disease
expressed as proportion of people with disease in whom the test comes as a positive
90 percent sensitive - test will prove positive to 90 percent of people who have the disease and 10 percent negative who has the disease
what is diagnostic accuracy ?
the ability to discern patient from true disease to non disease
what is the predictive value of a positive test ?
probability that a positive test
what is accuracy ?
how close the results obtained are to the actual true results
what is precision ?
repeatability - if the results obtained can be repeatable
when he precision is high and the accuracy is low it tends to be what type of error ?
a systemic error - inaccuracy is always in one direction
they cause ll the test results to be either high or low
due to calibration and reagent
what is random error ?
where there is poor precision and and low accuracy
