Which test assesses the function of the classical complement pathway?

Which test assesses the function of the classical complement pathway?

• A. CH50
• B. C3
• C. C4
• D. C1 esterase inhibitor level

Answer: (A)

The test evaluated is a functional assay that measures the overall activity of the classical complement pathway. It does this by assessing the serum’s ability to lyse antibody-coated target cells, typically using lysis of sensitized sheep red blood cells. The result reflects how well C1 through C4 (and the downstream components) can carry out the cascade to completion. If any component of the classical pathway is deficient or inhibited, this function drops, and the assay value decreases. In contrast, measuring C3 or C4 levels tells you how much of those components are present, not whether the pathway can function properly; levels can be normal or decreased for reasons like consumption or regulation. C1 esterase inhibitor level gauges regulation of the complement system rather than the functional integrity of the classical pathway itself. So the CH50 specifically targets the functional capacity of the classical pathway, making it the best choice.

The test evaluated is a functional assay that measures the overall activity of the classical complement pathway. It does this by assessing the serum’s ability to lyse antibody-coated target cells, typically using lysis of sensitized sheep red blood cells. The result reflects how well C1 through C4 (and the downstream components) can carry out the cascade to completion. If any component of the classical pathway is deficient or inhibited, this function drops, and the assay value decreases.

In contrast, measuring C3 or C4 levels tells you how much of those components are present, not whether the pathway can function properly; levels can be normal or decreased for reasons like consumption or regulation. C1 esterase inhibitor level gauges regulation of the complement system rather than the functional integrity of the classical pathway itself. So the CH50 specifically targets the functional capacity of the classical pathway, making it the best choice.