LDH activity measurement basics Steps:

• Recall that LDH activity in plasma is assayed by adding lactate/NAD+ substrate and monitoring NADH formation via spectrophotometry.
• Evaluate heating: it denatures enzymes, unnecessary for direct activity measurement.
• Evaluate substrate incubation: the assay requires mixing plasma with substrate and incubating, but option phrasing suggests optional pre-step, not core.
• Evaluate inhibitor: inhibitors block activity, irrelevant for measurement.

Not enough information to confirm C, as substrate incubation is typically required.

Why C is correct:

• C indicates no special preparation (heating or inhibitors) or extra incubation needed beyond standard assay mixing, aligning with direct plasma testing protocols.

Why the others are wrong:

• A requires inhibitor unnecessarily, which would reduce measurable activity.
• B requires heating, which destroys the enzyme.
• D duplicates C but lacks clarity in formatting.

Final answer: C