[Alizarin red S staining of calcium compound crystals in synovial fluid]

In order to study the clinical value of alizarin red S staining of calcium compound crystals in synovial fluid, the optimum conditions for staining and the detectable threshold of the crystals were examined. The staining of crystals was mainly affected by the concentration of the dye and pH of the solution. The best results were obtained with an alizarin red S concentration of 1.5-3.0% for hydroxyapatite (HA) and 2.0-3.0% for calcium pyrophosphate dihydrate (CPPD) crystal. The optimal pH of the solution was 4.0-6.0 for HA and 4.0-5.5 for CPPD crystal. For the detection of crystals phagocytosed by synovial fluid leukocytes, staining was enhanced by the addition of chloral hydrate to the dye solution which increased the permeability of the cell membrane. The detectable threshold levels of HA and CPPD crystal in synovial fluid by alizarin red S staining were 0.1 micrograms/ml and 0.5 micrograms/ml, respectively. These results suggest that alizarin red S staining is suitable for screening calcium compound crystals in synovial fluid, because it is more sensitive than other methods, such as polarized microscopy and X-ray diffraction. Alizarin red S staining was performed on 148 synovial fluids from patients with various joint diseases. The staining was positive in 100% of synovial fluids from patients with CPPD deposition disease, in 54% of fluids with osteoarthritis, and in 39% of fluids with rheumatoid arthritis. In osteoarthritis, the increase in the proportion of positive cases was found to be in accordance with the radiological grading of the joints.