False-Positive Clostridium difficile in Negative-Control Reactions Peak and Then Decrease with Repetitive Refrigeration of Immunoassay

Figure 1

Refrigeration cycles increased the OD₄₅₀ and false-positivity (convex correlation) in the ELISA wells of a valid nonexpired ELISA kit. The product insert of this ELISA kit instructed to bring all reagents to room temperature each time before testing. Positive-controls, not shown, performed as expected. The expired products yielded no positive or negative reactions as expected.