To clarify the deleterious effects of Mayer's haematoxylin staining procedure which result in a decrease in, or complete loss of, the number of calcium pyrophosphate dihydrate (CPPD) crystals, and to determine the proper staining period for preserving the crystals in a histological paraffin section of articular tissues.
Paraffin sections of CPPD crystal-bearing articular tissues of six patients were stained with Mayer's haematoxylin for 3, 8, or 15 minutes, and subsequently with eosin for one minute. The specimens were examined with an Olympus BHS polarised light microscope. The pH of Mayer's haematoxylin solution was measured with a TOA pH meter.
Positive birefringent CPPD crystals were seen clearly in all specimens stained with Mayer's haematoxylin for three minutes. The specimens stained for eight minutes showed a reduced number of crystals. No crystals were seen in the specimens stained for 15 minutes. Ordinary light microscopy showed no notable differences in the stainability of nucleus, cell membrane, and their surrounding tissues among specimens when stained with Mayer's haematoxylin for either 3, 8, or 15 minutes. The pH of Mayer's haematoxylin solution was 2.31.
To find CPPD crystals in the paraffin sections of articular tissues, the staining period with Mayer's haematoxylin should be limited to three minutes. The longer the staining period, the greater the reduction in the number of crystals owing to the strong acidity of the haematoxylin solution. A staining period of 15 minutes causes a complete loss of CPPD crystals.