Urate crystals: polarised light

Monosodium urate crystals cause gout. Identification in an appropriate sample provides evidence of crystal deposition.

Examine several fields and vary orientation relative to the compensator. Describe shape, intracellular or extracellular location and birefringence.

The field shows numerous long pointed yellow or blue structures among inflammatory cells. Some needles overlap cells.

The source identifies urate crystals. In practice, needle shape and negative birefringence support identification after correct technical assessment.

Calcium pyrophosphate crystals are often rhomboid or rod-shaped and weakly positively birefringent. Debris and artefacts must also be distinguished.

Relate the finding to the site and course of arthritis. Depending on context, request synovial fluid cell count and microbiological testing.

Suspected septic arthritis remains urgent even when crystals are present. Fever, immunosuppression or systemic illness increases concern.

Colour alone cannot establish the sign of birefringence without the compensator axis. A still field cannot replace examination of the sample.

Describe the needles, verify polarised-light findings and integrate the clinical picture; never use crystals alone to exclude infection.

• NICE NG219 — Gout: diagnosis and management (2022) ↗
• Gabriel Caponetti — document iconographique original / original image ↗

Documentary review: 2026-10-16