CO6 1. Quality Assurance 2. Clinical Enzymology Flashcards
Laboratory Quality Assurance Program
- whats this?
- Procedures and strategies to ensure that a
laboratory reports trustworthy results - Quality assurance programs assure both precision
and accuracy of test results
– e.g., run control samples - CRITICAL that your laboratory has a quality control
program
Pre-Analytical Considerations – Part of QA, too!
- Careful test selection
- +/- Fasting
- Correct tube
- Order of fill
- Adequate volume
- Collection technique
- Label tube correctly
- Fill out requisition form
- PROVIDE HISTORY
- Correct storage /
transportation To - Time lapse before analysis
- Always check with the laboratory prior to sending special samples
You Can Help! Post-Analytical Variables - Interpretation If something doesn’t fit:
- Be sure you’ve ordered the correct test for the case
- Understand reference intervals and cut-points
- Consult with colleagues / pathologists
<><> - Always interpret results in light of clinical picture
– EDTA contamination of serum tube
– Significant laboratory vs clinical changes
– Amylase increases with decreased GFR
– Platelet clumps, band neutrophils
> always look at a blood smear
<><>
Treat the patient, not the lab results
get a bunch of errors on a biochem printout, what to do?
- Look for an error message on the printout
- if there are errors, how long has this been going on?
should we use a lab or in house lab that does not maintain quality control?
A laboratory that does not maintain a Quality Assurance Program cannot ensure its test results are valid, and should not be used
Same goes for in-house laboratory equipment!
Disadvantages of In-House Tests
- Records are legally required
- Reference intervals?
- The in-house test result will be different than the reference laboratory result!
Advantages of Commercial Veterinary Laboratories
- Gold Standard
– Properly validated reference intervals
should each lab generate its own reference intervals? how many animal samples required?
- Should be generated by each lab
- Ideally >100 animals, minimum 40
Isoenzymes definition
- differ in animo acid sequence but catalyze the same reaction
– Occur in one or multiple tissues
<><> - Most are present in several tissues = isoenzymes
– Catalyze same reaction but originate from different tissues
Increased enzymes enter plasma by:
- Injury
- Decreased excretion
- Increased production
“Ideal” Diagnostic Enzyme qualities
Measured in serum
Assay simple to perform
Single cell type or tissue source
Increase = clinical disease process
how do we measure enzyme activity? decreases with what?
- have substrate in solution
- add enzyme
- measure product
<><>
Decreases with time / temperature - critical for some enzymes
- consider if a remote or ambulatory practice
what does it mean if we see increased enzyme activity in a lab result?
- Tissue injury & leakage of enzyme
- Increased production (induction)
- Decreased excretion
what does it mean if we see decreased enzyme activity in a lab result?
rarely significant
Tissue specificity of enzymes allows localization of
– Injury
– Increased production
Patterns of enzyme increase help us
– Understand disease processes
– Make diagnoses
how can we differentiate isoenzymes?
- by half life
> eg. ALP half-life in dogs is different depending on tissue source: 3d from liver, only 6 min from intestine, placenta, kidney
> Less commonly, ALP can be increased from intestinal inflammation, or bone sources - other tissue specific enzymes
> eg. ALP and ALT are found in liver
> ALT also found in muscle
> damaged liver: increased ALT (and sometimes ALP)
> ALT also occurs in skeletal muscle, but so is CK
> if we have eg. a broken femur, we see that evidence of catastrophic damage, as well as elevated CK, so we can be more confident that ALT is from muscle - route of excretion
> kidney origin GGT gets peed out; even if we have damage to renal tubular epithelial cells, GGT will not be increased
> however, if we have induction of GGT in the liver, we see increased GGT in biochem profile
Leakage Enzymes
- where are they found? when are they increased?
- Cytosol, organelles or both
> Injury
a) Sublethal / reversible
b) Necrosis
> ↑ activity detected within hours of injury on biochem profile
Most important liver leakage enzymes
ALT
AST
GLDH - used more for large animal
SDH - used in large animal
Most important muscle leakage enzymes
CK
AST
(ALT) - requires massive damage
Most important RBC leakage enzymes
AST - hemolysis
(CK)
amylase is a leakage enzyme from where?
pancreatic acinar cells
lipase is a leakage enzyme from where?
- pancreatic acinar cells
- hepatic tumours
Induced Enzymes
- usually found where? when do we see them?
- usually attached to cellular membranes; plasma membrane, or organelle membrane
- stimulus zaps the cell and tells it to increase production
> days rather than hours to increase
> when increased, the enzyme falls off the membrane, enters blood, increased activity can be measured - sometimes, if we have massive damage, these will also be released
<><>
Only two induction enzymes: - ALP
- GGT
two induction enzymes? where are they from?
Liver
- ALP, GGT
Bone
- ALP
administration of prednisone will induce what enzymes in the liver, in dogs? when else can we see these enzymes?
ALP, GGT
- also see with cholestasis, or when we have hyperbilirubinemia
> induction enzymes associated with the irritation that occurs from bile sitting between hepatocytes in the canaliculi
What enzyme is induced in hypothyroid cats? when else can we see it?
bone origin ALP
- also from lytic lesions involving bone, like multiple myeloma (holes on radiographs), bone tumor
Leakage vs Induced Enzymes
- why is the difference not clear cut?
- interpretation depends on what?
– Loss of leakage enzymes may lead to increased production
– Acute injury may cause a rapid increase in induced enzymes
<><>
Interpretation
* Depends on:
– Sources of enzyme & half-life
– Excretory route
– Assay method
– Clinical history
half life of CK compared to AST? how can we use that to our advantage?
- CK has shorter half-life than AST
> CK peaks early and decreases early
> AST takes longer to increase. Never goes as high as CK, then takes longer to decrease - if there is ongoing muscle damage, CK will remain high upon a second measurement!
> if first measurement has high CK and lower AST, and second has lowering CK and higher AST, we know we are winning
amylase can be increased with pancreatitis. how is it excreted? how can we use this info to help rule out pancreatitis?
- excreted renally
> any reason for a decrease in GFR, eg. dehydration, cardiac disease, shock, kidney disease, can also lead to increased amylase - if we see increased amylase, look at urea and creatinine (garbage products that are excreted renally)
> are they high? then we likely have a decreased GFR due to kidney disease
> use U/S, rest of clinical picture to rule out pancreatitis
does it matter if we use different assays and get different numerical results, but they are trending in the same direction?
no this is fine, the assays just use different methods. Don’t get stuck on it.
if we see elevated AST in an animal with hemolytic anemia, should we be worried about liver and/or muscle?
- not really, we know it has hemolytic anemia which can increase AST from RBCs
- resolve hemolytic anemia and check that AST trends down
what should we remember about the big picture when looking at enzyme values? 3 important considerations
- Biological variation
– Age, sex, species, breed, physiological status - Effects of drugs
– Steroids, anticonvulsants - Artifacts
– Collection, storage, transit time, assay type
Serum Enzymes Summary
- synthesized where?
- recognized how?
- increased enzyme activity meaning?
- Synthesized by various cell types – some serum activity normally present
- Recognized by increased activity in serum
- If enzyme activity ↑ there must be cellular damage or
- Production of enzyme increased due to a stimulus or
- Elimination of enzyme from body is decreased
– e.g., amylase & lipase are excreted renally
– In dogs and cats they can be increased with decreased glomerular filtration rate
why is DGGR lipase better than regular lipase for measuring?
Lipase - Pancreatic acinar cells, hepatic tumours
> DGGR lipase (AHL and Antech) is less affected by decreased renal excretion–more trustworthy!
ALP is found in which organs / situations?
- liver
- bone
- sometimes intestine
- prednisone administration in dogs
GGT is found in what organs / situations
- liver
- prednisone administration in dogs
ALT is found in what organs / situations
- liver
- muscle if damage is extreme
AST is found in what organs / situations?
- liver
- muscle
- hemolysed sample
CK is found in what organs / situations?
- muscle
- hemolysed sample
GLDH is found in what organs / situations?
liver
regular lipase is found in what organs / situations?
- pancreas
- Decreased GFR
DGGR lipase is found in what organs / situations?
pancreas
amylase is found in what organs / situations?
- pancreas
- decreased GFR
which enzymes are only used in large animal? small animal? both?
LA only: GLDH
SA only: ALP, ALT, lipase, amylase
Both: GGT, AST, CK
