Reflections on the use of controls in immunohistochemistry and proposal for application of a multitissue spring-roll control block.

The conventional positive control in immunohistochemistry consists of a separately immunostained slide containing tissue known to show positive reaction with the antibody. Although it can indicate that the reagents are sound, it cannot guarantee that the appropriate reagents have indeed been dispensed in the correct order on the test cases. Furthermore, positive controls are costly because they often account for 20% to 40% of all immunostained slides in a diagnostic surgical pathology laboratory. We describe a simple method to produce a multitissue spring-roll control block, comprising mostly normal tissues. The multitissue controls are mounted on the same slides of the test cases, and thus undergo the identical immunostaining procedures as the test tissues. Therefore they can provide the best assurance that the immunostains are working properly on the individual slides, the expected sensitivity is achieved, and the specificity is as expected. The wisdom of the conventional negative control is also questioned. When two or more immunostains are performed on a case, they should be sufficient to indicate the presence or absence of nonspecific staining.