Table 4.

Analytical methods that have been used for BCP detection

Technique	Advantages	Disadvantages
Imaging methods
Light and polarised microscopy	Inexpensive, widely available and useful for the larger crystals (>1 μm) that can occur	Inaccurate, non-specific and cannot detect BCP crystals. Polarised microscopy can aid detection of MSU and CPPD
Microscopy with staining	Inexpensive, widely available and can identify BCP crystal clumps	Sensitive but non-specific, false positive results are frequent. One dye is not enough to distinguish between the different types of crystals
Multi-dimensional microscopy	Coupling of multi-channel micro-spectrophotometer and 3-D relief imaging system to a microscope laser light scattering spectroscope	Not widely available. No evidence of clear identification of synovial fluid crystals
Transmission electron microscopy	Small sample size and can be used with electron diffraction	Expensive, complex, not widely available, operator-dependent
Scanning electron microscopy	Small sample size and can be coupled to X-ray elemental analysis	Expensive, complex, relies on morphology
Atomic force microscopy	Small sample size, minimal sample preparation. Can exploit hardness and lattice features in sample for detection and identification. Chemical force microscopy may offer more specificity	Operator-dependent, intricate to use on liquid samples, relies on morphology to an extent
Spectroscopic methods
FTIR	Accurate, used for automated pattern recognition methods	Can be misinterpreted and water interferes in certain parts of the spectrum
Raman	Accurate, water does not interfere, unique spectral signatures for each crystal type	Expensive, fewer library spectra available. Sample purification required to distinguish between various crystal types
Fluorescence	With correct dyes, can be very sensitive and selective	Requires special equipment; dyes can be expensive, not suitable for in vivo use
NMR/MRI	Can visualise most types of pathologies including crystal depositions	Very expensive, cannot identify nature of crystal deposition. Operator-dependent
Other methods
Calcium and phosphorus analysis	Well-understood assays such as atomic spectrometry, UV-Vis spectrophotometry, etc., can be selective and sensitive	Practical only in analysis of dissociated crystals, other matter present in the fluid can interfere
X-Ray diffraction	Accurate technique for unambiguous identification	Requires sample to be pure, dried and in sufficient quantity
Capillary electrophoresis	Can be used for pattern recognition analysis of synovial fluids containing crystals	Not applicable for direct separation of crystals
Radioassay	Allows semi-quantitative determination of BCP crystals	Involves radioactive reagents
Ferrography	Provides separation of particles by size/magnetic properties	Requires special sample preparation, only reflects general content of particles in synovial fluid