Flashcards in Biochemistry Enzymes and Biomarkers Deck (63):
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Enzymes are:
1. Intracellular catalysts
2. Measured by activity (U/L) or concentration (ng/L)
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Serum enzyme activity is a marker of
Tissue function or dysfunction
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Isoenzymes:
Enzymes of similar catalytic activity but structural differences, pattern may be helpful to localize origin, e.g. CK, ALP
e.g. alkaline phosphatase isoenzymes
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Clinical important enzymes:
• Liver enzymes
• Creatine kinase (CK)
• Amylase
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LFT looks at
Bilirubin
ALk Phosphatase (cholestasis measurement)
ALT – hepatocullar function
Total Protein
Albumin
Globulin
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Tranaminases types
ALT and AST (intracellular enzymes)
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ALT location
Largely confined to hepatic cytoplasm
Use routinely to test liver function
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AST location**
o Hepatic cytoplasm and mitochondria
o Skeletal and cardiac muscle (will rise post MI)
o Red blood cells (haemolysis causes increased0
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Causes of increased transaminase
>10 x ULN (>400 U/L)
• Acute hepatitis and liver necrosis
• Paracetamol poisoning
• Major crush injuries (AST)
• Severe hypoxia
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Increased Transaminase
5-10 x ULN (200-400 U/L)
• Chronic hepatitis
• Following surgery or liver trauma
• Myocardial infarction (AST)
• Skeletal muscle disease (AST)
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Increased Transaminase Usually <5x ULN (40-200 U/L) – upper limit of normal
• Other liver disease (e.g. drug induced)
• Pancreatitis
• Haemolysis (in vivo and in vitro) (AST)
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Haemolysis can cause
increased in AST
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Necrosis of the liver cells e.g. fatty liver disease LF shows
– AST rises more than ALT
• Non-alcohol fatty liver disease
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Tests of cholestasis:
Alkaline Bone phosphatase (ALP)
• Bone (osteoblasts) – can be seen in late childhood with finishing growing
• Liver (biliary tree and cell surface)
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Minor Sources of ALP
• Intestine (some patients, postprandial)
• Placenta (third trimester, variable)
• Rare cancers (e.g. germ cell)
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Causes of increased alkaline phosphatase
Physiological
• Pregnancy (third trimester) – usually use bile acids as test of choice for cholestasis
• Childhood – germ cell tumours
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Causes of increased alkaline phosphatase:
Pathological
Often >5 x ULN
• Cholestasis (intra – and extra hepatic)
• Cirrhosis
• Paget’s disease of bone (metabolic)
• Osteomalacia, rickets
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ALP - Usually <5 x ULN
Seen in
• Hepatitis
• Infiltrative liver disease
• IBD – ascending cholangitis
• Hepatic space-occupying lesions –obstruction drainage
• Bone tumours (primary and secondary) – Mets very common
• Renal bone disease (RARE)
• Primary hyperparathyroidism (longstanding)
• Healing fractures
• Osteomyelitis
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Pregnancy (late) disease:
• HeLLPs syndrome
• Obstetric Cholestasis
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Tests of cholestasis:
Not in liver function tests as very sensitive e.g. ptients with autumn virus (subclinical disease will cause a rise in γGT.
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Gamma glytamyl trnasferase (γGT)
Source – very sensitive
Liver
Kidney
Pancreas
Seminal vesicles
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γGT increased in
Cholestasis and hepatocellular damage
Also due to enzyme induction – alcohol, phenobarbitone, phenytoin, oestrogen
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γGT clinical uses
Detection of alcohol – via hyper-lipid detection – not extremely specific
Identification of the source of ALP (.e. Liver or Bone) – of γGT is normal then ALP likely to be coming from bone.
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γGT in alcohol abuse elevation due to
Enzyme induction
Structural damage – cholestasis e.g. alcoholic cirrhosis
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γGT is elevated in
50-66% of subjects consuming >80g/day
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γGT sensitivity in alcoholics
54-85%
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Predictive value of a positive test for the diagnosis of alcoholism is approximately
20% (if prevalence is 1%)
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AST/ALT elevated and normal alkaline phosphatase means that
Approx. 90% have hepatitis
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AST/ALT normal and elevated alkaline phosphatase means that
Approx. 90% have obstructive jaundice
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CK structurally
Two subunits: M and B
Three isoforms: MM, MB and BB
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CK skeletal muscle Often >10 x URL
Polymyositis
Rhabdomyolysis (trauma, drugs etc)
Duchemme muscular dystrophy
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CK skeletal muscle 5-10 x URL
Following surgery
Physical trauma
grand -mal convulsions
Myositis
Duchenne carriers
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CK skeletal muscle Usually <5 x URL
Physiological (Afro-Caribbeans
Hypothyroidism
Drugs (e.g. statins)
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Myocardium:
CK
Myocardial infarction
Cardiac Myopathy
Myocarditis
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MI Diagnosis methods
Cardiac Troponins (TnT, Tnl, TnC*) – 100% cardiac specific
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cTnl and cTnT
• Highly sensitivity for myocardial injury (different structurally form skeletal muscle)
• Not released until 4-6 hours after MI – not for acute
• 100% diagnostic sensitivity not achieved until 12 h - confirmatory
• Remain elevated for up to one week
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Amylase description
Exocrine pancreatic and salivary enzyme
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Amylase used in
Diagnosis of acute pancreatitis
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Amylase: Minor elevations are
Not specific *
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Amylase: Results are
Highly method dependent
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Amylase clearance
Kidney
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raised serum amylase activity:
Marked increase (>5x upper reference limit)
• Acute pancreatitis
• Severe diabetic ketoacidosis
• Severe renal glomerular failure (clearance)
• Perforated peptic ulcer
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raised serum amylase activity:
Moderate increase
• Other intra-abdominal disorders
• Renal dysfunction
• Salivary disorders
• Morphine
• Macromylasaemia
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Tumour Markers
Substance measured in body fluids in order to diagnose or stage malignancy, or monitor response to therapy:
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Tumour Marker types
Structural proteins
Enzymes
Secretion products
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Structural proteins
1. CEA, Mucins (CA125, 153, 199) – carbohydrate antigen (CA(
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Enzymes
2. PSA
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Secretion products
3. Thyroglobulin (medullary carcinoma of thyroid)
4. AFP (foetal life – then switches to albumin )- hepatocellular carcinoma indication.
5. BJP (benns johns proteins (myeloma etc. –B cell)
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Potential uses of Tumour Markers
1. To screen for early disease (useless)
2. To aid diagnosis (useless)
3. To stage disease and or assess prognosis
4. To monitor patients with disease
a. Assess response to Rx
b. Detect early relapse
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Practical use of tumour marker sin diagnosis:
1. To rule out disease in an anxious patient (selective screening)
2. To make a diagnosis when disease is strongly suspected
3. To identify primary in patients with signs of metastatic disease
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Sensitivity
The percentage of those with disease who test positive
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Specificity
The percentage of those without disease who test negative
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Higher cut off means
More specific but less sensitive
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Lower cut off means
More Sensitive but less Specific
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Positive predictive Value
% of those with a positive test result who have disease
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Negative Predictive Value
% with a negative test result who are free of disease
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Depend on
Sensitivity, specificity and prevalence
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PPV problems
Falls dramatically at low prevalence
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CA125
Screening high risk individuals (with ultrasound)
Diagnosis of ovarian mass
Monitoring RX
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CA153
Monitoring response of breast cancer to treatment
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AFP/HCG
Staging prior to orchidectomy
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CEA
Pre-op
Postop (but only if liver mets would be resected)
Monitoring treatment response (chemo)
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