How Useful are Serum Enzyme Assays Tissue Damage Diagnosis

1
How Useful are Serum Enzyme Assays Tissue Damage
Diagnosis?
Tom Roberts, Department of Biochemistry,
University of Oxford
Background It is common for patients to present
with conditions caused by, or involving damage to
tissues. In the case of damage to cardiac tissue
the enzyme Creatine Kinase (CK) is released into
the bloodstream. Similarly, the concentration of
Aspartate Aminotransferase (AST) is also raised
following hepatic damage and to a lesser extent
following a myocardial event. Aim The purpose
of this investigation is to establish whether the
levels of AST and CK can be used as a means of
diagnosing tissue damage by assaying several
patient samples. Null Hypothesis The CK and AST
assays will not be sensitive enough to indicate
tissue damage. Methodology Creatine Kinase The
CK reaction generates creatine phosphate.
Addition of the Fiske/Subbarow reagent generates
a blue colour, the intensity of which is
proportional to the concentration of creatine
phosphate. The absorbance at 660nm is then
measured on a spectrophotometer since the
concentration of creatine phosphate is
proportional to the concentration of CK.
Methodology Aspartate Aminotransferase The AST
catalysed reaction (producing oxaloacetate) was
linked to that of Malate Dehydrogenase that can
use oxaloacetate as a substrate with the
concomitant oxidation of NADH. The decrease in
the absorbance of NADH was measured
spectrophotometrically at 340nm. Concl
usion Patient 1 Liver dysfunction Patient 2
Myocardial infarct Patient 3 Myocardial
infarct Null Hypothesis Incorrect Serum enzyme
assays are very sensitive to changes in the
concentration of enzymes that serve as markers
for tissue damage and are a very useful
diagnostic tool in clinical biochemistry.