Introduction to Clinical Enzymology

Which statement best defines clinical enzymology as presented in the lesson?

• The study of how all proteins fold in cells

• The assay of enzyme(s) in body fluids, usually blood, for diagnostic use or for monitoring a clinical condition

• The measurement of DNA sequences to predict disease

• The nutritional analysis of enzymes in food

In clinical practice, why is enzyme activity often measured instead of enzyme protein concentration?

• Activity measurement is usually easier, by monitoring changes in substrate or product concentrations

• Protein concentration always gives incorrect results

• Only enzymes in tissues, not body fluids, can be measured

• Activity measurement is less specific and more prone to analytical variation

Which statement best describes why ‘normal’ plasma enzyme concentrations are maintained in healthy individuals?

• They equal intracellular concentrations because enzymes diffuse freely across membranes.

• They reflect a balance among cellular synthesis and release during cell turnover and the rate of clearance from circulation.

• They are determined solely by the number of mitochondria in tissues.

• They remain constant because enzymes are not degraded in plasma.

Which statement best explains why plasma enzyme levels can be high in acute cell damage but may fall in terminal severe liver disease?

• Acute damage releases enzymes rapidly from damaged cells, whereas terminal severe liver disease has few remaining hepatocytes to release enzymes

• Both acute and terminal liver disease cause constant induction of enzyme synthesis, so levels remain equally high

• Enzyme clearance from circulation stops in terminal liver disease, so levels fall

• Acute damage suppresses enzyme synthesis, and terminal disease boosts release

Which statement best explains why plasma amylase activity can be elevated without pancreatic damage?

• Amylase is a large protein degraded by plasma proteases before hepatic uptake

• Amylase is a relatively small enzyme that is normally cleared by the kidneys, so renal glomerular impairment can raise its plasma level

• Amylase has the longest biological half-life among serum enzymes

• Amylase is primarily removed by the reticuloendothelial system

After a myocardial infarction, which enzyme’s plasma level is expected to remain elevated longest due to its longer biological half-life?

• Creatine kinase (CK)

• Aspartate aminotransferase (AST)

• Lactate dehydrogenase (LDH)

• Amylase

Which strategy directly enhances the diagnostic precision of plasma enzyme analysis when localizing tissue damage?

• Measuring only one enzyme at a single time point

• Serial enzyme estimations

• Ignoring isoenzyme patterns

• Relying solely on patient-reported symptoms

Which tissue damage is MOST directly linked to a marked increase (often >5–10× the upper reference limit) in plasma AST?

• Hepatic steatosis (NAFLD)

• Myocardial infarction

• Cholestatic jaundice

• Malignant liver infiltration

Which tissue has the highest concentration of alanine aminotransferase (ALT, also called glutamate pyruvate aminotransferase, GPT)?

• Liver

• Skeletal muscle

• Kidney

• Heart

Which statement best explains why total plasma LDH is considered a non‑specific marker of cell damage?

• LDH is produced only by the liver and skeletal muscle.

• LDH is widely distributed in many tissues including cardiac muscle, liver, kidney, brain, skeletal muscle, and erythrocytes.

• LDH is secreted exclusively into plasma during inflammation.

• LDH activity is unaffected by hemolysis.