Download 05. Clinical enzymology (1)

CLINICAL
ENZYMOLOGY
Measurements of the activity of
enzymes in plasma are of
value in the diagnosis and
management of a wide variety
of diseases.
 Small amounts of intracellular
enzymes are present in the
blood as a result of normal cell
turnover. When damage to cells
occurs, increased amounts of
enzymes will be released and
their concentrations in the
blood will rise.
 However, such increases are not always
due to tissue damage.
 Other possible causes include:
 increased cell turnover
 cellular proliferation (e.g. neoplasia)
 increased enzyme synthesis (enzyme
induction)
 obstruction to secretion
 One international unit is the
amount of enzyme that will
convert one micromole of
substrate per minute per litre of
sample and is abbreviated as U/L.
 Katal (catalytic activity) is
defined as the number of mole of
substrate transformed per second
per litre of sample.
Disadvantages of enzyme
assays
 A major disadvantage in the use
of enzymes for the diagnosis of
tissue damage is their lack of
specificity to a particular tissue
or cell type. Many enzymes are
common to more than one
tissue.
 Second, some enzymes exist in
different forms (isoforms)
 Individual isoforms are often
characteristic of a particular
tissue: although they may have
similar catalytic activities
Alkaline phosphatase
(ALP)
 Normal serum level of ALP is 40-125 U/L
or 0.5-1.3 mmol/(hour L).
 This enzyme present in high
concentrations in the
 liver
 bone (osteoblasts)
 placenta
 intestinal epithelium.
 The causes of an increase in
plasma ALP activity
 Physiological increases are been
in pregnancy, due to the placental
isoenzyme, and in childhood (when
bones are growing), due to the
bone isoenzyme.
ACID PHOSPHATASE
(ACP)
 It hydrolyses phosphoric acid
ester at pH between 4 and 6.
 ACP is secreted by prostate cells,
RBC, platelets and WBC.
 Normal serum value for ACP is
2.5-12 U/L or 0.025-0.12
mmol/(hour L).
 ACP total value is increased in prostate
cancer and highly elevated in bone
metastasis of prostate cancer.
 ACP is therefore an important tumour
marker.
 ACP is present in high concentration in
semen, a finding which is used in
forensic medicine in investigation of
rape.
Aminotransferases
 Two aminotransferases are
used in diagnosis and
management: aspartate
aminotransferase (AST)
 and
alanine aminotransferase (ALT).
ASPARTATE AMINO
TRANSFERASE (AST)
 It is also called as serum glutamateoxaloacetate transaminase (SGOT).
 Normal serum level of AST is 8- 40 U/L or
(0.1-0.45 mmol/(hourL))
 It is significantly elevated in myocardial
infarction. It if moderately elevated in liver
diseases.
Measurement of cardiac
enzyme levels
 Measure cardiac enzyme levels at regular
intervals, starting on admission and
continuing until the peak is reached or until
3 sets of results are negative. Biochemical
biomarkers are useful for both diagnosis
and prognostication
Laboratory Diagnosis of
Myocardial Infarction
ALANINE AMINO
TRANSFERASE (ALT)
 It is also called as serum
glutamate-pyruvate transaminase
(SGPT).
 Normal serum level of ALT is 5-30
U/L or (0.1- 0.68 mmol/(hourL))
 Very high values (100 to 1000 U/L)
are seen in acute hepatitis, either
toxic or viral in origin.
 Both ALT and AST are increased in
liver diseases, but ALT >AST.
 Moderate increase (25 to 100 U/L)
may be seen in chronic liver disease
such as cirrhosis, and malignancy in
liver.
 Ritis coefficient (AST/ALT) in
normal conditions is
 1.33 ± 0,42.
LACTATE DEHYDROGENASE
(LDH) (LD)
 Normal value of LDH in serum is 100-200
U/L.
 Values the upper range are generally seen
in children. Strenuous exercise will slightly
increase the value. LDH level is 100 times
more inside the RBC than in plasma, and
therefore minor amount of hemolysis will
result in a false-positive test.
 This enzyme exists in body
tissues as a tetramer. Two
monomers, H and M, can
combine in various proportions
with the result that five
isoenymes of LD are known.
 So five combinations of H and
M chains are possible; H4,
H3M, H2M2, M3H and M4
 The iso-enzymes are usually
separated by cellulose acetate
electrophoresis at pH 8.6.
 Lactate dehydrogenase isoenzymes
(as percentage of total):
 LDH1
14-26 %
 LDH2
29-39 %
 LDH3
20-26 %
 LDH4
8-16%
 LDH5
6-16 %
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Increase in total LDH level is seen in
hemolytic anemias,
hepatocellular damage,
muscular dystrophy,
carcinomas,
leukemias,
and any condition which causes
necrosis of body cells.
Creatine kinase (CK)
 Normal serum value for CK is 15-100 U/L
for males and 10-80 U/L for females.
 CK is a dimer; each subunit has a
molecular weight of 40,000. The subunits
are called B for brain and M for muscle.
Three isoenzymes, BB, MM and MB,
occur.
 Normally CK2 (MB) iso-enzyme is only
5% of the total activity.
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Causes of an increased plasma creatine kinase
activity.
often >10 x ULN
polymyositis
rhabdomyolysis (e.g. trauma, malignant hyperpyrexia)
Duchenne muscular dystrophy
myocardial infarction
5-10 x ULN
following surgery
skeletal muscle trauma
severe exercise
myositis
carriers of Duchenne muscular dystrophy
usually <5 x ULN
physiological (Afro-Caribbeans)
hypothyroidism
drug (statin) treatment
NUCLEOTIDE
PHOSPHATASE (NTP)
 It is a marker enzyme for plasma
membranes and is seen as an ectoenzyme (enzyme present on the cell
membrane).
 Normal NTP level in serum is 2-10
U/L. It is moderately increased in
hepatitis and highly elevated in
biliary obstruction.
GAMMA GLUTAMYL
TRANSFERASE (GGT)
 It is seen in liver, kidney, pancreas,
intestinal cells and prostate gland.
 In the body it is used in the synthesis
of glutathione.
 Normal serum value of GGT is 645 U/L in male and 5-30 U/L in
female.
 This value is moderately
increased in infective hepatitis
and prostate cancers. The GGT
level is highly elevated in
alcoholism, obstructive
jaundice and neoplasm's of
liver.
PROSTATE SPECIFIC
ANTIGEN (PSA)
 It is produced from the secretory
epithelium of prostal gland. It is
normally secreted into seminal fluid
 Normal value is 1 -5 µg/L. It is very
specific for prostate activity. Values
between 4-10 µg/L is seen in benign
prostate enlargement; but values
above 10 µg/L is indicative of prostate
cancer.
 Interest in this enzyme derives largely
from the fact that it hydrolyzes a musclerelaxant drug, widely used in
anaesthesia, called succinylcholine
(scoline). Occasionally, patients are
found in whom the effect of this drug,
which paralyzes respiration, persists for
several hours after it has been
administered (scoline apnoea). Many of
these patients have an abnormal
cholinesterase activity.
GLUCOSE-6-PHOSPHATE
DEHYDROGENASE
 This is an important enzyme in the
hexose monophosphate shunt pathway
of glucose.
 Normal value of GPD in RBC is 125250 U/1012 cells.
 It is mainly used for production of
NADPH. It has a special role in the RBC
metabolism.
AMYLASE
 This splits starch to maltose. It is
activated by calcium, chloride and
fluoride ions.
 It is produced by pancreas and
salivary glands
 Normal serum value is 50-120 U/L,
(12-32 g/(hour× L)).
LIPASE
 It will hydrolyse triglyceride to βmonoglyceride and fatty acid.
 The enzyme is present in pancreatic
secretion.
 Normal serum range is 0.2-1.5
U/L.
Enolase
 It is a glycolytic enzyme. Neuronspecific enolase (NSE) is an isoenzyme seen in neural tissues and
Apudomas. NSE is a tumour marker for
cancers associated with neuroendocrine origin, small cell lung
cancer,neuroblastoma,pheochromocyt
om, medullary carcinoma of thyroid,
etc.
 Upper limit of NSE is 12 μg/ml.