CLINICAL ENZYMOLOGY
PREPARED BY MR. ABHIJIT DAS
ENZYMES OF DIAGNOSTIC IMPORTANCE IN LIVER DISEASES:
ALT (ALANINE AMINOTRANSFERASE):
ALT is primarily found in the liver and is released
into the bloodstream when liver cells are damaged.
Elevated levels of ALT are indicative
of liver damage, which can occur due to conditions such as hepatitis,
cirrhosis, or fatty liver disease.
AST (ASPARTATE AMINOTRANSFERASE):
AST is also found in liver cells and released into
the bloodstream when liver cells are damaged.
However, AST is less
specific to the liver and can also be elevated in conditions affecting
other organs, such as the heart or muscles.
AST levels are often used in conjunction with ALT
levels to assess liver health.
ALP (ALKALINE PHOSPHATASE):
ALP is an enzyme found in various tissues throughout
the body, including the liver, bones, and bile ducts.
Elevated ALP levels can indicate liver diseases such
as bile duct obstruction, liver cancer, or certain bone disorders.
GGT (GAMMA-GLUTAMYL TRANSFERASE):
GGT is primarily found in the liver and bile ducts.
Elevated GGT levels are often
associated with liver diseases such as hepatitis, alcohol-related liver
disease, or bile duct obstruction.
ENZYMES OF DIAGNOSTIC IMPORTANCE IN MYOCARDIAL INFARCTION:
CK (CREATINE KINASE):
Creatine kinase (CK), also known as creatine
phosphokinase (CPK), is an enzyme found primarily in the heart, brain, and
skeletal muscles.
It plays a crucial role in energy metabolism,
specifically in the conversion of phosphocreatine
and adenosine diphosphate (ADP) into adenosine triphosphate (ATP), which
provides energy for muscle contractions.
In myocardial infarction (heart
attack), CK is released into the bloodstream when there is damage to heart
muscle cells. Therefore, elevated levels of CK in the blood can indicate
myocardial injury.
However, CK levels may also be elevated in other
conditions affecting skeletal muscles or the brain.
CARDIAC TROPONINS:
Cardiac troponins are proteins found in cardiac
muscle cells (myocytes) and help in the regulation
of muscle contraction.
They consist of three subunits:
troponin C, troponin I, and troponin T. In
the context of myocardial infarction (heart attack),
troponin I and troponin T are the most clinically relevant.
When there is damage to cardiac muscle
cells, such as during a heart attack, troponins are released into the
bloodstream. This makes cardiac troponins highly sensitive and specific
biomarkers for diagnosing myocardial injury.
[NOTE: Troponin I and troponin T are the most
clinically relevant cardiac troponins because they are specific to cardiac
muscle tissue. But, Troponin C is found in both cardiac muscle (myocardium) and
skeletal muscle.]
AST (ASPARTATE AMINOTRANSFERASE):
Aspartate aminotransferase (AST), also known as
serum glutamic oxaloacetic transaminase (SGOT),
is an enzyme found in various tissues throughout the body, including the heart,
liver, skeletal muscles, kidneys, brain, and red blood cells. AST plays a role
in amino acid metabolism and is involved in the conversion
of aspartate into glutamate.
In myocardial infarction (heart
attack), AST levels may increase due to damage to cardiac muscle cells
(myocytes).
However, AST is less
specific to the heart compared to cardiac-specific biomarkers like
troponin I and troponin T.
Elevated AST levels can also occur in liver
diseases, skeletal muscle injury, renal injury, and other conditions affecting
tissues where AST is present.
LDH (LACTATE DEHYDROGENASE):
Lactate dehydrogenase (LDH) is an enzyme found in
various tissues throughout the body, including the heart, liver, skeletal
muscles, kidneys, brain, and red blood cells.
LDH plays a crucial role in anaerobic
metabolism by catalyzing the interconversion of lactate and pyruvate. This
process is essential for energy production in cells, especially under conditions
of low oxygen availability.
In myocardial infarction (heart
attack), LDH levels may increase due to damage to cardiac muscle cells
(myocytes).
However, LDH is less
specific to the heart compared to cardiac-specific biomarkers like
troponin I and troponin T.
Elevated LDH levels can also occur in liver
diseases, skeletal muscle injury, kidney injury, and other conditions affecting
tissues where LDH is present.
ENZYMES OF DIAGNOSTIC IMPORTANCE IN MUSCLE DISEASES:
CK (CREATINE KINASE):
CK is an enzyme found primarily in muscle tissues,
including skeletal and cardiac muscle.
It catalyzes the
conversion of phosphocreatine into ATP, providing energy for muscle
contraction.
Elevated levels of CK in the blood are
indicative of muscle damage or breakdown. CK levels are often
elevated due to ongoing muscle damage.
ALDOLASE:
Aldolase is an enzyme involved in
glycolysis, the metabolic pathway that breaks down glucose for
energy production. It catalyzes the conversion of fructose-1,6-bisphosphate
into two three-carbon molecules: dihydroxyacetone phosphate (DHAP) and
glyceraldehyde-3-phosphate (G3P).
Elevated aldolase levels in the blood
are also indicative of muscle damage or breakdown, particularly in conditions
affecting skeletal muscle.
ENZYMES OF DIAGNOSTIC IMPORTANCE IN BONE DISEASES:
ALP (ALKALINE PHOSPHATE):
Alkaline phosphatase (ALP) is an enzyme found in
various tissues throughout the body, including bone, liver, intestine, kidney,
and placenta.
In the context of bone disease, ALP is particularly
relevant due to its role in bone metabolism.In bone, ALP
is produced by osteoblasts, which are bone-forming cells. It plays a
critical role in bone mineralization by promoting
the deposition of calcium and phosphate ions, which are essential
components of bone tissue.
Elevated levels of ALP in the blood
can indicate increased bone turnover, which may occur in various bone diseases,
including osteoporosis, bone fractures etc.
ENZYMES OF DIAGNOSTIC IMPORTANCE IN PROSTATE CANCER:
PSA (PROSTATE SPECIFIC ANTIGEN):
PSA is a protein produced by the prostate gland and
is typically found in semen, but a small amount of
it enters the bloodstream.
The primary function of Prostate-Specific Antigen
(PSA) is to liquefy semen. Liquefaction of semen refers to the process by which
semen changes from a gel-like consistency to a more fluid state shortly after
ejaculation.
Elevated levels of PSA in the blood
can indicate prostate-related issues, including prostate cancer.
While PSA testing is widely used as a screening tool
for prostate cancer, it's important to note that elevated PSA levels can also occur due to some non-cancerous conditions such
as prostatitis (inflammation of the prostate).
PSA testing is often used alongside other diagnostic
tests, such as digital rectal examination (DRE) and imaging studies, to help
diagnose and monitor prostate cancer.
ACP (ACID PHOSPHATASE):
Acid phosphatase is an
enzyme found in high levels in the prostate gland.
The primary function of ACP is to
maintain the appropriate pH and viscosity of semen
Historically, ACP testing was used as a diagnostic
marker for prostate cancer before the widespread
use of PSA testing.
While its use has declined with the advent of PSA
testing, ACP may still be measured in certain cases, particularly when PSA
levels are inconclusive or in advanced prostate cancer cases.
Elevated ACP levels can indicate
prostate cancer, although it is less specific compared to PSA.