Which ELISA format is typically used to quantify a cytokine concentration in serum?

• A. Sandwich or capture ELISA
• B. Indirect ELISA
• C. Competitive ELISA
• D. Direct ELISA

Answer: (A)

Quantifying a cytokine in serum works best with a sandwich (capture) ELISA because it uses two antibodies that recognize different parts of the same cytokine. One antibody is fixed to the plate to capture the cytokine from the serum, and a second antibody, labeled for detection, binds a different epitope on the captured cytokine. This dual-recognition approach provides high specificity and sensitivity in a complex sample, giving an accurate readout over a dynamic range suitable for serum concentrations.

Indirect ELISA is designed to detect antibodies in a sample, not the cytokine itself, so it isn’t appropriate for measuring cytokine levels. Competitive ELISA can quantify antigens but is generally less sensitive and more affected by matrix effects in serum, making it less favorable for routine cytokine quantification. Direct ELISA detects antigen using a labeled antibody without a secondary capture step, which typically offers lower specificity in complex samples like serum.