Evaluation of a biochemical panel Flashcards
How can we use standard deviations to establish if a biochem result is normal or not?
3 + 4 standard deviations - very unlikely to be healthy
If a analytical test has poor precision what do we need to be cautious of?
need to be cautious about making diagnostic decisions about results that are quite close to cut off values
e.g., a test with an analytical imprecision of 19% - a result of 12 could mean the actual value is anywhere between 7.3-16.6 - which can either mean the value is actually normal or severely abnormal if the result is close to the cut-off value
Give examples of factors that can cause biochem results to be wrong
Haemolysis, icterus and lipaemia
Post-prandial
EDTA contamination
Unphysiological values
Limits of techniques (min and max reportable conc)
What are the different methods of profile interpretation?
Step by step (go down list of abnormal results creating differential lists, and carrying on adding and eliminating differentials)
Pattern match (using experience to identify trends)
Give examples of biochem markers that suggest liver damage vs liver dysfunction
Damage:
- Leakage enzymes (ALKP, ALT, AST, CK)
Dysfunction:
- hepatic function (bile acid, ammonia, albumin, glucose, bilirubin)
Give examples of biochem markers that suggest pancreatic damage vs dysfunction
Damage:
- pancreatic enzymes (Lipase, PLI)
Dysfunction:
- pancreatic function (TLI)
Give examples of biochem markers that suggest thyroid damage vs dysfunction
Damage:
- TgAA
Dysfunction:
- T4, TSH
Give examples of biochem markers that suggest renal damage vs dysfunction
Damage:
- casts
Dysfunction:
- creatinine
- USG
- proteinuria
Give examples of biochem markers that suggest cardiac damage vs dysfunction
Damage:
- Troponin I
Dysfunction:
- NT-proBNP
How can we assess the degree of liver damage by biochemistry?
AST + glutamate dehydrogenase are in the mitochondria and ALT, AST are found in cytoplasm therefore need significant damage to get an increase in those enzymes
ALP found in biliary tree so more likely to increase with less damage
However, AST can come from muscle and ALP can come from bone, GIT or be steroid induced
Size of result change cannot be used to establish degree of damage as a small injury can release a large amount of enzymes - cannot use to assess prognosis
What is another possible reason for increased liver enzymes other than damage or dysfunction
Enzyme induction by pathology or drugs/endogenous compounds (e.g., glucocorticoids or barbiturates)
Describe the use of ALT measurements in biochemistry
Liver specific in dogs and cats (not large animals)
Earlier and higher levels following hepatic damage than AST
Why should an ALT and ALKP measurements be repeated after 2-3 days in dogs?
to determine if the cause has passed, is ongoing or worsened
Half life in dog = 40-60hrs
Half life in cats = 3.5hrs (pathology must be ongoing for this result in cats)
Describe the use of ALKP measurements in biochemistry
Located in membrane (canalicular)
Induced by impaired biliary flow and medications
Not liver-specific (iso-enzymes):
- bone growth
- intestinal
- canine steroid induced
Dog T½ = 60-70 hrs
Cat T½ = 6 hours
Intestinal enzyme T½ <10mins (rarely see increase due to intestinal problem)
Susceptible to non-hepatic disease e.g., ‘old dog’ and secondary hepatic effects - serum GGT more biliary/liver specific
Give examples of non-primary hepatopathies that cause raised liver enzymes
Enzyme induction/toxin in other disease:
- Stress, Glucocorticoids, e.g. pyometra
Liver central to a lot of metabolic processing
- Diabetes, fatty liver, hyperlipaemia
Portal circulation
- Hepatocyte impact of pancreatic and GI pathology
Blood supply and oxygenation
- Cardiac congestion, anaemia
What are the next steps after identifying elevated liver enzymes
Rule out therapies (including topical eye, ear and skin)
Rule out systemic, pancreatic, GI disease
Multiple enzyme abnormalities, very high results +/- bilirubin – can’t ignore possible primary liver disease
Further tests:
- bile acids
- ACTH stim (test for HAC)
Monitor and act if worsened
What does elevated urea and normal creatinine suggest?
Pre-renal effects:
- Reduced renal perfusion (dehydration) (measure USG to assess hydration)
- Post-prandial
- Unusually high urea with normal creatinine → GI bleeding
Focus on creatinine as measure of renal function
What does hyposthenuria with azotaemia suggest?
‘inappropriately dilute’
Functional kidneys:
- excessive fluid intake (primary polydipsia)
- ADH production or action
What are possible differentials for a reduced Na:K ratio?
Hypoadrenocorticism (Addison’s)
Pre-analytic (e.g., Akitas, non-dogs, high WBX or platelet counts)
GI disease
Renal dysfunction
Effusions
Give examples of possible differentials for raised glucose?
stressed cat
could be indicator of pre-diabetes in cats:
- if cat not stressed
- if persistent
- all other investigation normal
Measure fructosamine to determine significance of raised glucose
Give examples of differentials for hypercalcaemia
Give examples of differentials for hypocalcaemia
Parathyroid dependent - primary hypoparathyroidism:
- immune mediated
- post-surgical
demand exceeds supply/mobilisation:
- periparturient tetany (eclampsia)
- nutritional deficiency of Ca or VitD
- pancreatitis with fat necrosis
Which biochem tests relate to hydration?
TP
Albumin
Which biochem tests are renal related?
Urea
Creatinine
Phosphate
Ca
Urinalysis
Which biochem tests are hepatic related?
Liver enzymes
bile acids
urea
albumin
glucose
Which biochem tests are muscle related?
CK
AST
myoglobinuria
Which do biochem electrolyte levels (Na, Cl, K) relate to?
Hydration
Renal
GI
Endocrine
What biochem tests are pancreatic related?
ALKP
ALT
Lipase
Glucose
Ca
Which biochem results are nutrition related?
albumin
glucose
bilirubin
Describe the variation of the usefulness of urea levels on biochemistry results between species
GI tract and other clearance mechanisms make urea levels unhelpful in equidae and ruminants as indicator of renal function
Uric acid in uricotelic species
Describe the variation in bilirubin biochem tests between species
Elevated in anorexic horses and cattle with normal hepatic function
describe the variation in Ca biochemistry result use between species
Horses excrete excess calcium through kidney – renal failure could give rise to genuine hypercalcaemia
Egg laying species will generate high tCa (increase in protein bound fraction – ovalbumin) but normal iCa
Describe the variation in electrolyte biochem test results use between species
Low Na, Cl, elevated K common in large animal diarrhoea, less so in dogs and cats
