Gout Analyzer May Successfully Diagnose Gout and Calcium Pyrophosphate Deposition

Synovial fluid crystal analysis can be performed using a gout analyzer for diagnosis of gout and calcium pyrophosphate deposition (CPPD) with certainty, in the absence of a standard compensated polarized microscope, according to results of study published in Modern Rheumatology.

Diagnosis of gout via presence of monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals in synovial fluid is typically performed with a compensated polarized microscope. However, these microscopes are not often available within hospitals. Investigators attempted to validate the use of a gout analyzer (U-GAN®; Evident Corporation, formerly known as Olym-pus) for identification of MSU and CPP during synovial fluid crystal analysis.

The investigators examined samples of knee synovial fluid suspected to contain CPP crystals. The samples were analyzed within 48 hours of collection, without being centrifuged.

Examinations were performed blindly, by one or more rheumatologists using 3 different methods: (1) with an optical microscope under normal light, (2) with the same microscope using compensated polarization provided by a gout analyzer, and (3) with a fully equipped compensated polarized microscope with a rotating stage as the gold standard.

In addition, laboratory technicians analyzed fresh, centrifuged synovial fluid using a gout analyzer as a reference.

Of the 30 samples obtained and examined using a compensated polarized microscope, CPP and MSU crystals were found in 11 and 4 noncentrifuged samples, respectively.

The rheumatologists detected crystals in noncentrifuged synovial fluid using ordinary light vs with a gout analyzer with a detection rate of 73.3% and 80%, respectively.

The detection rate among the laboratory technicians was 100% in fresh centrifuged synovial fluid using a gout analyzer.

While the investigators concluded that a gout analyzer can be used in settings where a compensated polarized microscope is unavailable, they noted, “In this study, the sensitivity increased to 80.0% with U-GAN®. U-GAN® allows the axis of the λ-plate to be rotated to achieve better compensation, but fine adjustments cannot be made. In contrast, a fully equipped compensated polarized microscope allows the observer to rotate each crystal by using the rotating stage to determine its birefringence. Therefore, distinguishing MSU and CPP crystals from other, birefringent particles in synovial fluid may be easier with a fully equipped compensated polarized microscope than with U-GAN®.”