Survival of calcium pyrophosphate crystals in stored synovial fluids.

Eleven synovial fluids containing calcium pyrophosphate dihydrate (CPPD) were examined repeatedly over an eight week period to assess whether storage conditions and duration influenced the number of crystals present. Aliquots of each fluid were stored at room temperature, 4 degrees C, and -70 degrees C. At -70 degrees C there was no change in crystal count after eight weeks' storage. At room temperature and 4 degrees C crystal counts declined slowly over the eight week period, though CPPD crystals were still readily apparent after eight weeks in 10/11 (4 degrees C) and 8/11 (room temperature) fluids. No change in crystal morphology was detected and, apart from one fluid kept at room temperature in which fungal hyphae were noted at six weeks, no new crystals were seen. Calcium pyrophosphate dihydrate crystals in synovial fluid can be maintained for prolonged periods by freezing.