Evaluation of biochemical panel Flashcards
How are reference intervals determined?
Based on central 95% of clinically normal animals
Ideally, derived from ≥120 healthy animals, but often estimated from smaller groups
What is a cut-off value in diagnostic testing?
fixed threshold with defined sensitivity & specificity for disease
More useful in high-prevalence diseases
How can we use standard deviations to establish if a biochem result is normal or not?
Mean +- 2SD = normal
3-4SD = very unlikely to be healthy
Why should borderline results be interpreted cautiously?
Lab imprecision (Coefficient of Variation CV%) affects reliability
Example: If cut-off is 10, with a CV of 19%, result of 12 might actually be between 7.3–16.6.
Pre-analytical factors (haemolysis, lipaemia, contamination) can affect results
Repeat tests or use alternative methods if in doubt
Give examples of factors that can cause biochem result to be incorrect
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 & carrying on adding & eliminating differentials)
Pattern match (using experience to identify trends)
What steps should you take when interpreting lab results?
Review results objectively—don’t be biased by previous differentials
Check if “normal” values align with case
Don’t ignore outliers without reason—they may be relevant
Create pathophysiological story that explains all abnormalities
Why is clinical context crucial when interpreting lab results?
Same abnormality can mean different things in different patients
Example:
- High glucose in 2 cats: One may be stressed, other truly diabetic
- Isosthenuria in 2 dogs: One may be azotaemic, other not
What markers indicate liver damage vs. dysfunction?
Damage (Leakage Enzymes): ALT, AST, ALKP, CK
Dysfunction: Bile acids, ammonia, albumin, glucose, bilirubin
What markers indicate pancreatic damage vs. dysfunction?
Damage: Lipase, PLI (pancreatic lipase immunoreactivity)
Dysfunction: TLI (Trypsin-like Immunoreactivity)
What markers indicate thyroid damage vs. dysfunction?
Damage: TgAA
Dysfunction: T4, TSH
What markers indicate renal damage vs. dysfunction?
Damage: Casts in urine (indicate tubular damage)
Dysfunction: Creatinine, USG (urine specific gravity), proteinuria
What markers indicate cardiac damage vs. dysfunction?
Damage: Cardiac Troponin I
Dysfunction: NT-proBNP (marker of heart failure)
How can we assess the degree of liver damage using biochemistry?
ALT & AST are cytoplasmic enzymes that increase with significant hepatocellular damage
AST & GDH (Glutamate Dehydrogenase) are also found in mitochondria, requiring severe damage for elevation
ALP is located in biliary tree & can increase with mild cholestasis or enzyme induction
Non-liver sources: AST can rise due to muscle injury, while ALP may originate from bone, GIT, or steroid induction
Magnitude of enzyme elevation does NOT correlate with prognosis—small injuries can release large amounts of enzymes
What causes enzyme induction rather than true cell damage?
Enzyme induction by pathology or drugs/endogenous compounds (e.g. glucocorticoids or barbiturates)
Describe use of ALT measurement in biochemistry
Liver specific in dogs & cats (not large animals)
Earlier & higher levels following hepatic damage than AST
Why should ALT & ALKP measurements be repeated in dogs after 2-3 days?
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)
How is ALKP used in biochemistry?
Located in canalicular membranes; induced by biliary stasis & medications
Not liver-specific—isoenzymes also come from:
- Bone growth (young animals)
- Intestinal mucosa
- Steroid induction (dogs)
Half-life (T½):
- Dogs: 60–70 hours
- Cats: 6 hours
- Intestinal ALKP: <10 minutes (rarely detected in blood).
Increases in non-hepatic conditions: Age-related (“old dog”), secondary liver effects.
Serum GGT is more biliary/liver-specific than ALKP
Give examples of non-primary hepatopathies that cause elevated 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 & 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 hypostenuria with azotaemia suggest?
‘inappropriately dilute’
Functional kidneys:
- excessive fluid intake (primary polydipsia)
- ADH production or action
What is the significance of the Na:K ratio?
Na:K <22 suggests hypoadrenocorticism (Addison’s disease)
Other causes: GI disease, renal dysfunction, effusions.
Check Na+ and K+ separately before interpreting
Mild abnormalities may not be Addison’s—confirm with ACTH stimulation test
What should you consider with elevated glucose?
Cats: Stress-induced hyperglycemia common
Persistent hyperglycemia → Pre-diabetes or diabetes mellitus
Fructosamine helps differentiate stress vs. true diabetes.
Give examples of causes of hypercalcaemia
Give examples of differentials for hhypocalcaemia
Parathyroid dependent - primary hypoparathyroidism:
- immune mediated
- post-surgical
demand exceeds supply/mobilisation:
- periparturient tetany (eclampsia)
- nutritional deficiency of Ca or Vit D
- pancreatitis with fat necrosis
Which biochem tests relate to hydration?
TP
Albumin
Which biochem results are nutrition related?
albumin
glucose
bilirubin
What biochem tests are pancreatic related?
ALKP
ALT
Lipase
Glucose
Ca
Which do biochem electrolyte levels (Na, Cl, K) relate to?
Hydration
Renal
GI
Endocrine
Which biochem tests are muscle related?
CK
AST
myoglobinuria
Which biochem tests are hepatic related?
Liver enzymes
bile acids
urea
albumin
glucose
Which biochem tests are renal related?
Urea
Creatinine
Phosphate
Ca
Urinalysis
Describe the variation in ALT results in biochem between species
Dog T½ = 40–60h, Cat T½ = 3.5h
Mild ALT (& ALKP) increases are more concerning in cats
Not liver-specific in horses & ruminants—use GLDH & SDH instead
Why is urea unreliable for assessing renal function in some species?
Equids & ruminants: GI excretion reduces its reliability for kidney assessment
Uric acid is used instead in uricotelic species (birds, reptiles)
Creatinine is a better renal function marker in large animals
How does calcium metabolism vary between species?
Horses excrete excess Ca via kidneys, so renal failure can cause true hypercalcemia
Egg-laying species (birds, reptiles) have high tCa due to protein-bound Ca (ovalbumin) but maintain normal iCa
Always check iCa when interpreting hypercalcemia
Why is bilirubin elevated in anorexic horses and cattle?
Fasting/anorexia leads to bilirubin buildup without liver disease
Horses lack a gallbladder, so bilirubin metabolism differs from other species
Bilirubin elevation ≠ liver dysfunction in these species
What are the key acute phase proteins (APPs) (inflammatory markers) in different species?
Equine: Serum Amyloid A (SAA), fibrinogen
Cattle: Haptoglobin
Dogs: C-reactive protein (CRP)
Cats: Alpha-1 acid glycoprotein (AGP)
Large animals rely more on APPs than neutrophil counts for inflammation detection
What electrolyte imbalances are common in large animals?
Large animal diarrhea → Low Na, Cl, high K
Less common in small animals
What blood tubes promote coagulation?
Plain glass/Z serum
Clot activator tube (CAT)
SST with gel
What blood tubes impede coagulation?
Sodium citrate
EDTA
Heparin
Sodium fluoride
Citrate
What blood tubes are used for haematology?
EDTA
What blood tubes are used for clinical biochemistry?
Serum
Plasma
What blood tubes are used for glucose?
Fluoride
What blood tubes are used for coagulation tests?
Citrate
What are important considerations for anti-coagulant tubes?
Take care not to touch inside of tube when filling (to avoid contamination of other tubes & thus artefacts)
Fill to the designated line
Gently invert after filling (to mix any additives)
What are important order of fill/draw considerations of blood tubes?
Take serum samples before EDTA & don’t take citrate tube as first sample (use discard tube if necessary)
