Glossary of Clinical Lab: Liver enzymes, Panreatic enzymes
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- Functions of the liver
- -major site for synthesis of proteins, endogenous lipids, and lipoproteins
-major site for metabolism of lipid soluble drugs and other toxic compounds
-involved in storage of energy as glycogen
-vitamins A, D, B12
-endorcrine organ that synthesizes angiotensinogen and triiodothyronine
-site for clearance for many hormones (inuslin, parathyroid hormone, estrogen, cortisol)
- Purpose of Liver function tests?
- -give indication of hepatic structure, intregity, and function
-measure substances released by damaged tissues
-measures substances metabolized/produced by the liver
-used for screening, identifying, and monitoring pts with liver disease
- Liver enzymes include:
- -alkaline phosphatase (ALP)
-Aspartate aminotransferase (AST); formerly SGOT
-Alanine Aminotransferase (ALT); formerly SGPT
-Lactate dehydrogenase (LDH)
-Gamma glutamyltransferases (GGT)
- How are patterns in enzyme changes determined?
- liver injury determines the pattern
- Cytoplasic enzymes
- Example of cytoplasmic related injury
- cell death resulting in leakage of cytoplasmic enzymes LDH, AST, ALT
- Mitochondrial enzymes
- Examples of mitochondrial injury
- alcohol rapidly releases mitochondrial AST
- Example of canalicular injury
- obstructive process and accumulation of bile acids releases canalicular enzymes ALP and GGT
- -alkaline phosphatase
- Where is ALP found?
- -liver, bone, biliary tract, epithelium, intestinal mucose, placenta
-each source has its own isoenzymes
- What is ALP used for?
- -index of liver and bone disease
-enzyme rises in proportion to new bone cell production
-blood levels rise when excretion from the liver is impaired
- ALP is normally elevated in...
- children due to bone growth
- Liver and biliary tract excrete ALP into the ...
So if bile ducts are blocked, ALP ends up in the serum
- Increased ALP suggests:
- -liver tumor or absess
-drug induced liver dz
-biliary tract obstruction
- -aspartate aminotransferase
- AST elevated in...
- -following MI
-liver disease or injury
-liver tumor or absess
-drug or ETOH damage
- AST is a good indicator of...
- acute liver cell damage
bc levels rise and fall quickly
- -Alanine Aminotransferase
- ALT is found in..
-small amts in kidney, heart, and skeletal muscle
- Elevation in ALT suggests...
- -liver disease
-can help sort out binge drinker from alcoholic
- ALT vs AST
- -elevated to same degree in hepatitis, mono, drug induced acute liver injury
-ALT less than AST in acute alcoholic liver disease or active cirrhosis
-ALT elevated longer than AST d/t longer half life
-ALT often used to confirm AST elevations are d/t liver injury
- -Gamma Glutamyltransferase
- Where is GGT found?
- -mainly in liver
-small amounts in biliary tract, heart, intestine, brain, pancreas and spleen
- GGT is elevated in...
- -active liver disease (acute damage or biliary obstruction)
-chronic ETOH use and binge drinking
- GGT is NOT elevated in...
- -bone disease, growth or pregnancy (unlike ALP)
-not significantly elevated with normal ETOH use
- Differences between ALP, ALT, AST and GGT
- -ALP increases in bone disease, bone growth, and pregnancy whereas others do not
-GGT may help confirm that rise is d/t liver damage
-AST is more sensitive thand ALT for acute alcoholic liver disease or active cirrhosis
-GGT has same or better sensitivy as ALP for obstruction
-GGT has better sensitivity for tumor than ALP
-GGT elevated with same frequency as AST for actue liver injury
ALT often used to confirm AST elevations are d/t liver injury
-ALT and AST elevated to same degree in hepatitis, mono, drug induced acute liver injury
- Bilirubin basics
- -results from metabolism of heme (found in hemoglobin, myoglobin, and cytochromes
-byproduct of hemolysis (RBC destruction)
-small amount in serum is normal
-is cleared in liver
- Unconjugated bilirubin (Indirect)
- -found in serum
-NOT water soluble
-cannot get into urine
- Conjugated bilirubin (Direct)
- -water soluble
-normally excreted in the bile after being processed in the liver
- Normal ranges of bilirubin:
- Total < 1.5 mg/dl
Direct < 0.4 mg/dl
Indirect cannot be measured, must be calculated
Take note that there is usually far more unconjugated (indirect) than conjugated (direct)
- Extra-hepatic biliary tract obstruction
- -common bile duct obstruction (gall stones, carcinoma at the head of pancreas)
-conjugated bilirubin rises initially
-as levels of conjugated bilirubin rise, it becomes protein bound and ratio of conjugated to unconjugated approached 1:1 (usually there is far more unconjugated bilirubin)
- Intra-hepatic biliary tract obstruction
- -from liver cell injury (hepatitis, cirrhosis, drugs, mononucleosis)
-conjugated and unconjugated both rise
-conjugated rises d/t blockage of small bile passages between cells
-unconjugated rises d/t inability of the liver to conjugate/metabolize
- Pts >60 with a bilirubin increase:
- Cancer 45%
- pts 30-60 with total bilirubin (indirect and direct) increase:
- viral infection 30%
- Pts <30 with bilirubin increase:
- viral >80%
- Normal level of total bilirubin rules out....
- any significant impairment of the excretory function of the liver or excesive hemolysis of RBCs
- Bilirubin: Critical Values
- Newborn >15 mg/dl (treatment is initiated or mental retardation may result)
Adult >12 mg/dl (indicated sever liver problems)
- mental retardation secondary to increased bilirubin
To prevent/treate, put under UV light which breaks down bilirubin
- Hepatic Function Panel
- Pancreatic enzymes
- -secreted from pancreatic cells into pancreatic duct
-aids in catabolism of carbs in the intestines
- Amylase test used to ..
- -detect and monitor pancreatitis
-often ordered when pt presents with acute abdominal pain
- Abnormal values rise and normalize...
- -rise within 12 hours of onset of disease
-clear within 48-72 hours of initial insult (cleared by kidneys)
- Do abnormal levels of amylase correlate with severity of disease?
- No, levels rise and fall easily - they do not indicate how severe the disease is
- Amylase increases in...
- -pancreatic disease
-intestinal obstruction or infarction
-obstructed salivery duct
- -secreted by pancreas into duodenum to break down triglyerides
-excreted by kidney
- Lipase test is used for..
- acute pancreatitis
- Lipase increases in...
- -pancreatic disease
-intestinal obstruction or infarction
- Lipase elevation and normalization
- -peaks at 24-48 hours
-normalizes in 7-10 days
- Lipase vs Amylase
- -lipase levels parallel the rise in amylase but rise later (peak 24-48 hours vs 12 hrs)
-lipse levels normalize later than amylase (7-10 days vs 48-72 hrs)
-lipase is less sensitive but more specific then amylase as indicator for pancreatitis
-amylase will rise with blocked salivary duct as well
- Serum immunoreactive trypsin
- -produced only by pancreas
- SIT increases with...
- pancreatitis (95% of the time)
- Advantages of SIT
- VERy specific and VERY sensitive (~95%)
- Disadvantages of SIT
- not widely available
time delay in results
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