Needle-like crystals that can be seen in synovial fluids of patients with gout.

Can be differentiated from pseudo-gout with a polarizing microscope. Monosodium Urate crystals are yellow when parallel to the axis and blue when perpendicular, opposite of calcium pyrophosphate.

Typically small rhomboid, square, or rodlike crystals. Can be seen in synovial fluid of patients with pseudogout.

Can be differentiated from true gout with a polarizing microscope. Calcium pyrophosphate is blue when parallel to the axis and yellow when perpendicular, opposite of monosodium urate crystals.

Cholesterol crystals have a notched plate appearance and are birefringent. Lipid droplets may also be visible, appearing as Maltese crosses under polarized light.

Can be seen in patients with rheumatoid arthritis.