Quality control by tissue microarray in immunohistochemistry

Aims: An external positive control section is included in each immunohistochemical analysis as a well recognised and validated technique for standardising results. The method is time-consuming and expensive. On the contrary, internal controls are warranted and inexpensive, but their use is only feasible in selected diagnoses. The aim of this work is to show how the method of the authors allows improving the interpretation and cuts costs in the immunohistochemical analysis of bone marrow specimens. Methods: A paraffin-embedded tonsil tissue cylinder was sampled from a donor block using an automated sampler and included as an 'internal control' together with a bone marrow biopsy in a recipient block, avoiding the use of external tonsil tissue control. To validate this technique, the authors compared the quality of immunohistochemistry, the workload and costs with routine external control in 50 consecutive bone marrow biopsies. Results: Processing simultaneously the sample and the tissue control in the same block, 60 external positive control tests were spared. Only a few minutes were taken for the preparation of the recipient blocks, and no particular technical skill was required. Considering that the volume of antibodies used for the analysis of each sample was not increased, a considerable amount of the disposable material was saved. The workload of technicians was decreased and some potential technical bias was avoided. The time required for pathologists to interpret the slides was also reduced. Conclusions: In conclusion, this seems to be a feasible, cost-cutting and quality-improving technique, not limited to haematopathology but potentially extensible to other fields of pathology.