Chem lect 21: Eval musculoskeletal and hepatic systems Flashcards
(58 cards)
1
Q
Reference intervals (RI) for enzymatic assays
A
- RI’s needed to interpret results of patient
- Different instruments/reagents produce different results for enzymes
- eg temperature of assay
- Best to RI’s for your lab especially for enzymes
- not as much difference for hematology assays
2
Q
Why would enzymes increase in the blood?
A
-
cellular leakage of enzyme
- cytoplasmic release following plasma membrane damage or fragmmentation
- blebosomes
- release of cytosol or organelles following necrosis
- cytoplasmic release following plasma membrane damage or fragmmentation
-
increased synthesis of enzyme (induction)
- by existing cells
- by hyperplastic/neoplastic cells
- decreased inactivation or clearance of enzymes
- ex: renal excretion of amylase
- absorption of maternal enzymes in colostrum
- (ALP and GGT in certain neonates)
3
Q
Physiochemical features that influence diagnostic use
(i.e. lead to inc enzyme activity in blood)
A
- enzyme activity in target cell > blood
- long enough half-life (hours) so enzyme accumulates in blood prior to activation
- access to blood vs fate of enzyme from luminal epithelium
- directly
- lymphatics
4
Q
Biometrics of ‘ideal’ diagnostic test
(ENZYMES)
A
- want high sensitivity
- test detects sick patients
- Want high specificity
- normal results when disease is absent
5
Q
Exceptions to clinical significance
A
- Certain enzymes
- ALP in cats
- GGT in dogs and cats
- SDH
- Low grade inflammatory lesion (vs acute ‘flare up’)
- decreased number of target cells
- necrosis or fibrosis
- decreasing enzye activity may be a bad sign
- organ function tests more reliable than enzyes
- Inhibitors of enzye activity
- pancreatic lipase
* dec enzyme activity below RI is not clinically significant
6
Q
Muscle-origin enzymes
A
- CK, AST, LDH
- increases attributed to ‘leakage’ from injured skeletal myocytes
- reversible vs irreversible injury
- increased enzyme activity correlates with number of injured cells
- not type of injury (mild, necrotic, etc)
* can’t tell if damage is reversible or irreversible
* can’t tell if cells are damaged or dead
7
Q
Causes of myopathies
A
- Traumatic
- HBC, downer, post-op, IM injections
- Exertional
- exercise, endurance, seizures, trailering
- Degenerative
- rhabdomyolysis, Senna, capture mypathy
- Inflammation
- clostridial myositis
- Nutritional
- Vit E/Se deficiency
- Ischemic
- Saddle thrombus
- Metabolic
- equine glycogen storage
8
Q
Creatine kinase
CK
A
- Leakage
- Source
-
skeletal (+ cardiac/smooth)
- muscle, brain
- Isoenzyes not used
-
skeletal (+ cardiac/smooth)
- Serum half life
- very short (hours)
- Clinical application
- highly specific and sensitive for myopathies
- Overly sensitive
- inc (>3X) in animals w/o significant myopathy
9
Q
Aspartate aminotransferase
AST
A
- Leakage
- Source
- sk muscle
- hepatocytes
- other cells (Incl RBCs)
- Serum half life: hours to days
- Clinical applications
- sensitive, but low specificity (muscle vs. liver origin)
- need other specific enzymes (CK, ALT) to ID tissue source of leakage
- sensitive, but low specificity (muscle vs. liver origin)
10
Q
Lactate dehydrogenase
LDH
Not a test question
A
- Leakage
- Sources: multiple
- skeletal muscle
- liver
- WBCs
- RBCs
- Serum half-life: varies
- Clinical application: not much
- Not includedin chem panels
11
Q
ALT in muscle damage
A
- Mild elevations of ALT may be seen in dogs and cats
- liver disease is most usual cause of increases in these enzymes
- young dogs with muscular dystrophy
- inc CK, ALT
- dystrophic deficient cats
- inc CK, ALT
12
Q
Uncommon blood changes in massive rhabdomyolysis
A
- release of intracellular analytes from myocytes
- hyperkalemia
- hyperphosphatemia
- creatine => inc creatine
13
Q
Muscle Disease beyond routine chem panel
A
- Urine myoglobin (skeletal)
- Plasma troponins (skeletal, cardiac)
- Pro-BNP, Pro-ANP (cardiac)
14
Q
Muscle Disease
A
- Myoglobin
- muscle necrosis releases myoglobin
- freely filters into urine > myoglobinuria
- Urine ‘dipstick’ reacts to blood, hemoblobin and myoglobin
- Clinical signs
- enzymes
- urinalysis
- CBC can help differentiate
15
Q
Troponin
Not on test
A
- Cytosolic myofibrillar protein (not an enzyme) released from damaged cardiac and skeletal muscle
- Cardia troponin (cTI) specific for detecting myocardial disease
- Measured by immunoassay
16
Q
Natriuretic peptides
A
- released in response to cardiac myocyte stretch
- vasodilation
- natiuresis
- Inc blood levels with inc cardiac myocyte stretch/stress
- Commercially available (IDEXX)
17
Q
Natriuretic Peptides
Pro-BNP
A
Preliminary investigations in veterinary medicine
- causes of dyspnea
- Screen occult heart disease
- Predict morbidity/mortality with cardiac disease
18
Q
Liver physiology
What can go wrong
A
- Makes most proteins (albumin)
- Makes most coagulation factors
- Makes fuel
- glucose, glycogen, lipoproteins
- Makes cholesterol
- membranes and hormones (cortisol and testosterone)
- Makes tihngs to eliminate
- urea and bilirubin
- Processes RBCs and hemoglobin
- Detoxifies endogenous and exogenous chemicals and drugs
- Filters bacteria from portal blood
19
Q
Serum/plasma chemistry tests for detection of liver disease
A
- hepatic damage
- hepatocellular injury
- leakage enzyme
- cholestasis
- induced enzymes
- hepatocellular injury
- Decreased hepatic function
- synthetic function tests (albumin)
- Excretory function tests (bilirubin)
20
Q
Liver tests
A
- Hepatocyte injury or ‘leakage’
- ALT, AST, SDH
- Cholestasis
- ALP, GGT
- Liver function
- direct tests: bile acids, ammonia
- in healthy animals, 95% of bile acids are removed from portal blood and recycled by liver
- indirect tests
- total bilirubin, albumin, glucose, BUN, cholestasis, coagulation factors
- direct tests: bile acids, ammonia
21
Q
Enzyme Abbreviations
- ALT
- AST
- SDH
- LDH
- CK
- GGT
- ALP
A
- ALT: (Almost) Always Liver Test
- AST: A Sometimes (liver) Test
- could be from muscle or lysed RBCs
- SDH: Sick Depressed Horse (test)
- LDH: Lotta Darn Help (not)
- CK: Cramp Knot (test)
- muscle
- GGT: Grungy Gall Test
- ALP: A Liver Possibility
22
Q
ALT
Alanine aminotransferase
A
- Leakage
- Source:
- hepatocytes
- skeletal muscle in dogs/cats
- Serum half-life: hours/days
- Clinical application:
- sensitive and specific for hepatocellular injury in dogs/cats
- not used in ruminants, horses, swine
23
Q
AST
Aspartate aminotransferase
A
- Leakage
- Source
- skeletal muscle
- hepatocytes
- other tissues incl RBCs
- Serum half life: hours/days
- Clinical application
- sensitive, but low specificity
- muscle vs liver
- need ALT and CK for comparison
- sensitive, but low specificity
24
Q
SDH
Sorbitol dehydrogenase
A
- Leakage
- Source
- hepatocytes
- Half life: hours
- Clinical application
- very sensitive and specific for hepatocellular injury
- used mostly for horses, ruminants and swine
- increases not very marked
- limited availability of test, ustable storage
25
Comparison of enzyme activities in blood during active liver vs. muscle disease
26
Cholestasis (impaired biliary flow)
* between hepatocytes and duodenum
* Intrahepatic
* canaliculi and hepatic biliary duct flow affected
* Extrahepatic
* gall bladder and common bile duct flow affected
* Markers: Tbili, Chol, Bile Acids, ALP, GGT
* Distinction not possible with chemistry tests
* need imaging or surgery
27
Bile acids made from
* cholesterol backbone
28
Examples of cholestatic dzs
* hepatocellular swelling from accumulatin of lipid or glycogen
* inflammation (hepatitis, cholangiohepatitis, cholangitis)
* Neoplastic cell infiltration
* Common bile duct obstruction (colethiasis, pancreatitis) or leakage
* Disruption of hepatocellular bilirubin excretion
* functional cholestasis (e.g. sepsis)
29
Cholestatic enzymes
ALP, GGT
* Cholestatis **induces** synthesis of ALP and GGT which are bound to cell membranes
* ALP on canalicular surface of hepatocytes is cleaved by phopholipase
* activated by increased bile acids during cholestasis
* crosses cell to sinusoidal slurface and enters blood
* Cholestasis causes biliary epithelium to undergo hyperplasia
* then synthesizes more GGT
* requires days for inc in induced inzyme activity vs immediate release of leakage enzyes
30
ALP mostly comes from
Hepatocytes
31
GGT mostly comes from
biliary epithelium
32
Alkaline phosphatase
ALP
* Source
* Hepatocytes
* biliary epithelium
* osteoblasts
* colostrum
* half-life
* varies with isoform and species
* 3 days dog
* 6 hours cat
* Variable sensitivity for cholestasis and low specificity
* depends on species
* many sources of ALP
33
Inc ALP activity
* Cholestasis Dog \> Cattle \> Cat, horse
* **inc ALP precedes hyperbilirubinemia**
* **Feline ALP: any inc is important**
* Iatrogenic elevation in **dogs**
* **glucocorticoid induction**
* **phenobarb**
* Young animals have inc ALP from bone or bone abnormalities
* non-healing fractures
* osteosarcoma
* animals
* **Colostrum ingestion** (dog, cats) few days
* Late pregnancy of cats (placental ALP)
* Mammary neoplasms
34
Gamma glutamyltransferase
GGT
* Source
* **biliary epithelium**
* **renal tubules**
* renal tubular GGT detected in urine **not blood**
* Half-life: 3 days
35
Increased GGT activity
* **Cholestasis**
* **more specific (vs ALP) for cholestasis**
* More sensitive (vs ALP) in **cats, horses, cattle**
* bottom line: assay ALP and GGT?
* Colostrum ingestion of mammary GGT a few days postnatal
* puppies, calves
* Drug induction in dogs
* less effect vs ALP
* Steroids
* phenobarbital
36
Overview of liver function tests
Excretory
Synthetic
* Excretory
* **bilirubin**
* bile acids
* ammonia
* Synthetic
* **albumin**
* **urea (BUN)**
* **cholesterol**
* **glucose**
* coagulation factors
\*tests (n=5) on routine chemistry panels
\* notice missing hepatic tests....
37
BIlirubin as a hepatic function test
* Routinely available
* less sensitive for hepatic function vs bile acids
* variable sensitivity for cholestasis
* less so in dogs
38
Metabolic pathway of bilirubin
* Hemoglobin degraded to unconjugated bilirubin
* Unconjugated bilirubin binds to albumin in plasma, travels to liver
* Liver conjugates bilirubin to make it more soluble for excretion
* Excretion through biliary tract into intestine
39
Categories of hyperbilirubinemia
Pre-hepatic
hepatic
post hepatic
* Pre-hepatic
* mostly unconjugated
* Hepatic
* mix of unconjugated/conjugated
* Post-hepatic
* mostly conjugated
\*icterus clinically evident when total bilirubin \> 1.5 mg/dL
40
Tests for bilirubin
Blood and urine
Total bilirubin
bilirubin splits
urinary bilirubin
urinary urobilinogen
* Total bilirubin (plasma/serum)
* routine chem panel
* Bilirubin 'splits' (plasma/serum)
* special request
* direct
* conjucated (including delta bili)
* indirect
* unconjugated (calculated)
* Urinary bilirubin (urine dipstick)
* interpretation for bilirubinuria in dogs vs cats
* Urinary urobilinogen (urine dipstick)
* not clinically imp
41
Bilirubin tests in the real world
* Typically just inc total bilirubin, don't request splits
* Best candidate for determining splits
* anorectic horses with suspected liver dz
* Categorize 'pre-hepatic' or 'hepatic/post-hepatic' using other data
* PCV for anemia
* ches for liver dz
* leukograms for sepsis
42
Metabolism of bile acids
* Synthesized from cholesterol in hepatocytes
* conjugated and excreted into bile
* 'stored' in gall bladder
* CCK causes release into small intestine from gall bladder
* **Aids in fat digestion**
* Reabsorbed in ileum, enters portal circulation
* **uptake/clearance by hepatocytes from portal veins**
* highly efficient clearance (90% 1st pass)
* Enterohepatic cycle re-starts (95% overall recovery)
* small losses in feces, urine
\*not on routine panels
43
Bile acids excreted into....
Should not be inc in....
Duodenum
Peripheral blood samples
44
Basis for bile acid testing
* Evaluates **excretion** and subsequent **clearance** of bile acids by hepatocytes
* Requires healthy
* **hepatocytes**
* intestinal absorption
* **portal circulation**
* Detects
* hepatocellular dz
* shunting vessel concerns...
* cholestasis
* hepatic circulation disorders (+malabsorption?)
* Very sensitive and specific for liver dz in all species
45
Bile acid testing
Indications and procedure
* Not a routine test ($$)
* Indicated when hepatic enzymes/function tests are minimally altered but liver dz still suspected
* **NOT** indicated if hyperbilirubinemia of hepatic origin is present
* redundant
* Fasting (8-12 hours)
* postprandial (2 hrs post small meal) serum samples in dogs/cats
* postprandial more sensitive
* single test in ruminants and horses
46
Increased bile acids
* Decreased hepatic clearance
* **portosystemic shunts**
* **hepatocellular disease**
* Decreased hepatic biliary excretion
* **intrahepatic and extrahepatic cholestasis**
* functional cholestasis
* e.g. extrahepatic sepsis
47
Maltese dog bile acid results
## Footnote
Fasting: 36 ug/dL H [0-10]
Postprandial: 45 ug/dL H [0-20]
* maltese dog thing:
* we don't no what the hell goes on with them
* not indicative of active liver dz
48
Mixed breed bile acid results
## Footnote
Fasting 25 ug/dL H [0-10]
Postprandial 18 ub/dL [0-20]
* Considerations
* **Event during fasting**
* spontaneous gall bladder contraction
* bile flow bypassed gall bladder
* gall bladder contracts whenever it wants (CCK contracts gall bladder)
* postprandial more sensitive for liver dz
* Technique
* dog vomited fat meal before stimulating gallbladder release...?
49
Problems with sensitivity/specificity
* excess fat
* induces post-prandial **lipemia** that intereferes with absorbance
* therapeutic use of bile acids
* ursodeoxycholic acid....? may or may not affect assay
* falsly **decreased** results if severe intestinal dz
* PLE: decreases intestinal reabsorption of bile into protal circulation
50
'Ammonia'
(ammonium, NH4)
Significance
* Produced from protein degradation by enteric bacteria
* absorbed by intestines and cleared from protal circulation by hepatocytes
* enters urea cycle
* hepatic detoxification
* SIgnificance
* accumulates during liver disease
* \>60% loss of functional mass
* role in **hepatic encephalophathy**
* causes neurologic signs =\> these make us want to run ammonia tests
51
Ammonia test procedure
* ammonia can be generated in tube after collection
* must send on ice
* must analyze within a couple of hours
* should maybe send a normal sample too to rule out handling problems
* bile acids much less complicated
52
Hyperammonemia
rule outs
\*typically run on fasted blood sample
* hepatocellular dz (dec uptake)
* Hepatic vascular shunts (PSS)
* urea cycle disorders (rare)
* **urea toxicosis in ruminants**
* **non protein nitrogen**
53
Decreased concentrations of analytes synthesized by hepatocytes
\* not sensitive or specific but useful in concluding liver disease
* albumin
* urea
* cholesterol
* glucose
* clotting factors
54
Effects of decreased hepatic synthesis
Hypoalbuminemia
Dec BUN
Hypocholesterolemia
Hypoglycemia
Coagulopathy
* Hypoalbuminemia
* Late event in liver disease (80% loss function)
* Other causes
* **inflammation**
* renal or intestinal loss + hyperglobulinemia?
* Dec BUN
* Polyuria from inabilty to conc urine
* Hypocholesterolemia
* also from cholestasis
* Hypoglycemia (late, 80% loss, least likely?)
* hyperglycemia with decreased hepatic uptake
* Coagulopathy
55
Coagulation disorders in liver dz
* Dec synthesis of coagulation factors
* Dec activation of Vit K dependant factors (II, VII, IX, X)
* Liver necrosis causes DIC
* Dec clearance of FDPs, activated coagulation factors
56
Bilirubin on urine dipstick....
Always bad in cats
Shows up in urine before it shows up in blood... I think
57
Ammonium biurates and bilirubin crystals
58
Microcytosis
Microcytosis in absence of anemia
* decreased liver function could mean less processing of cholesterol to make the lipid bilayer of cell wall membrane
* something about processing iron
Microcytosis in absence of anemia
* shunts
* dec liver function
* japanese breeds
\*microcytosis not very sensitive
