Biochemistry Enzymes and Biomarkers Flashcards
Enzymes are:
- Intracellular catalysts
2. Measured by activity (U/L) or concentration (ng/L)
Serum enzyme activity is a marker of
Tissue function or dysfunction
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
Clinical important enzymes:
- Liver enzymes
- Creatine kinase (CK)
- Amylase
LFT looks at
Bilirubin ALk Phosphatase (cholestasis measurement) ALT – hepatocullar function Total Protein Albumin Globulin
Tranaminases types
ALT and AST (intracellular enzymes)
ALT location
Largely confined to hepatic cytoplasm
Use routinely to test liver function
AST location**
o Hepatic cytoplasm and mitochondria
o Skeletal and cardiac muscle (will rise post MI)
o Red blood cells (haemolysis causes increased0
Causes of increased transaminase
>10 x ULN (>400 U/L)
- Acute hepatitis and liver necrosis
- Paracetamol poisoning
- Major crush injuries (AST)
- Severe hypoxia
Increased Transaminase
5-10 x ULN (200-400 U/L)
- Chronic hepatitis
- Following surgery or liver trauma
- Myocardial infarction (AST)
- Skeletal muscle disease (AST)
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)
Haemolysis can cause
increased in AST
Necrosis of the liver cells e.g. fatty liver disease LF shows
– AST rises more than ALT
• Non-alcohol fatty liver disease
Tests of cholestasis:
Alkaline Bone phosphatase (ALP)
• Bone (osteoblasts) – can be seen in late childhood with finishing growing
• Liver (biliary tree and cell surface)
Minor Sources of ALP
- Intestine (some patients, postprandial)
- Placenta (third trimester, variable)
- Rare cancers (e.g. germ cell)
Causes of increased alkaline phosphatase
Physiological
- Pregnancy (third trimester) – usually use bile acids as test of choice for cholestasis
- Childhood – germ cell tumours
Causes of increased alkaline phosphatase:
Pathological
Often >5 x ULN
- Cholestasis (intra – and extra hepatic)
- Cirrhosis
- Paget’s disease of bone (metabolic)
- Osteomalacia, rickets
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
Pregnancy (late) disease:
- HeLLPs syndrome
* Obstetric Cholestasis
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.
Gamma glytamyl trnasferase (γGT)
Source – very sensitive
Liver
Kidney
Pancreas
Seminal vesicles
γGT increased in
Cholestasis and hepatocellular damage
Also due to enzyme induction – alcohol, phenobarbitone, phenytoin, oestrogen
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.
γGT in alcohol abuse elevation due to
Enzyme induction
Structural damage – cholestasis e.g. alcoholic cirrhosis
γGT is elevated in
50-66% of subjects consuming >80g/day
γGT sensitivity in alcoholics
54-85%
Predictive value of a positive test for the diagnosis of alcoholism is approximately
20% (if prevalence is 1%)
AST/ALT elevated and normal alkaline phosphatase means that
Approx. 90% have hepatitis
AST/ALT normal and elevated alkaline phosphatase means that
Approx. 90% have obstructive jaundice
CK structurally
Two subunits: M and B
Three isoforms: MM, MB and BB
CK skeletal muscle Often >10 x URL
Polymyositis
Rhabdomyolysis (trauma, drugs etc)
Duchemme muscular dystrophy
CK skeletal muscle 5-10 x URL
Following surgery Physical trauma grand -mal convulsions Myositis Duchenne carriers
CK skeletal muscle Usually <5 x URL
Physiological (Afro-Caribbeans
Hypothyroidism
Drugs (e.g. statins)
Myocardium:
CK
Myocardial infarction
Cardiac Myopathy
Myocarditis
MI Diagnosis methods
Cardiac Troponins (TnT, Tnl, TnC*) – 100% cardiac specific
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
Amylase description
Exocrine pancreatic and salivary enzyme
Amylase used in
Diagnosis of acute pancreatitis
Amylase: Minor elevations are
Not specific *
Amylase: Results are
Highly method dependent
Amylase clearance
Kidney
raised serum amylase activity: Marked increase (>5x upper reference limit)
- Acute pancreatitis
- Severe diabetic ketoacidosis
- Severe renal glomerular failure (clearance)
- Perforated peptic ulcer
raised serum amylase activity:
Moderate increase
- Other intra-abdominal disorders
- Renal dysfunction
- Salivary disorders
- Morphine
- Macromylasaemia
Tumour Markers
Substance measured in body fluids in order to diagnose or stage malignancy, or monitor response to therapy:
Tumour Marker types
Structural proteins
Enzymes
Secretion products
Structural proteins
- CEA, Mucins (CA125, 153, 199) – carbohydrate antigen (CA(
Enzymes
- PSA
Secretion products
- Thyroglobulin (medullary carcinoma of thyroid)
- AFP (foetal life – then switches to albumin )- hepatocellular carcinoma indication.
- BJP (benns johns proteins (myeloma etc. –B cell)
Potential uses of Tumour Markers
- To screen for early disease (useless)
- To aid diagnosis (useless)
- To stage disease and or assess prognosis
- To monitor patients with disease
a. Assess response to Rx
b. Detect early relapse
Practical use of tumour marker sin diagnosis:
- To rule out disease in an anxious patient (selective screening)
- To make a diagnosis when disease is strongly suspected
- To identify primary in patients with signs of metastatic disease
Sensitivity
The percentage of those with disease who test positive
Specificity
The percentage of those without disease who test negative
Higher cut off means
More specific but less sensitive
Lower cut off means
More Sensitive but less Specific
Positive predictive Value
% of those with a positive test result who have disease
Negative Predictive Value
% with a negative test result who are free of disease
Depend on
Sensitivity, specificity and prevalence
PPV problems
Falls dramatically at low prevalence
CA125
Screening high risk individuals (with ultrasound)
Diagnosis of ovarian mass
Monitoring RX
CA153
Monitoring response of breast cancer to treatment
AFP/HCG
Staging prior to orchidectomy
CEA
Pre-op
Postop (but only if liver mets would be resected)
Monitoring treatment response (chemo)
PSA
Diagnosis if used with DRE 9+/-)
Monitoring RX
