A Point-of-Care Raman Spectroscopy-Based Device for the Diagnosis of Gout and Pseudogout: Comparison With the Clinical Standard Microscopy.

OBJECTIVE: To demonstrate the usefulness of a novel medical device based on Raman spectroscopy for the rapid point-of-care diagnosis of gout and pseudogout. METHODS: A shoebox-sized point-of-care Raman spectroscopy (POCRS) device was developed for use in the diagnosis of gout and pseudogout. The device included a disposable syringe microfiltration kit to collect arthropathic crystals from synovial fluid and a customized automated Raman spectroscopy system to chemically identify crystal species. Diagnosis according to the findings of POCRS was compared with the clinical standard diagnosis based on compensated polarized light microscopy (CPLM) of synovial fluid aspirates collected from symptomatic patients (n = 174). Kappa coefficients were used to measure the agreement between POCRS and CPLM findings. RESULTS: Overall, POCRS and CPLM results were consistent in 89.7% of samples (156 of 174). For the diagnosis of gout, the kappa coefficient for POCRS and CPLM was 0.84 (95% confidence interval [95% CI] 0.75-0.94). For the diagnosis of pseudogout, the kappa coefficient for POCRS and CPLM was 0.61 (95% CI 0.42-0.81). CONCLUSION: Kappa coefficients indicated that there was excellent agreement between POCRS and CPLM for the diagnosis of gout, with good agreement for the diagnosis of pseudogout. The POCRS device holds the potential to standardize and expedite the time to clinical diagnosis of gout and pseudogout, especially in settings where certified operators trained for CPLM analysis are not available.

Analysis of crystals leading to joint arthropathies by Raman spectroscopy: comparison with compensated polarized imaging.

The current study assessed the feasibility of the application of Raman spectroscopy toward the diagnosis of gout and pseudogout. First, the lowest concentrations of monosodium urate monohydrate (MSUM) and calcium pyrophosphate dihydrate (CPPD) crystals detectable by Raman spectroscopy were investigated by mixing known amounts of synthetic crystals with synovial fluid in the concentration range of 1 to 100 microg/mL. Second, a digestion protocol was developed for clinical samples to improve crystal extraction. The ensuing centrifugation of the digest congregated crystals at a well-defined point and allowed for point-and-shoot Raman analysis without having to conduct an extensive search for individual crystals. Finally, synovial fluid samples obtained from patients (n = 35) were cross-analyzed by polarized light microscopy (PLM) and the Raman method to compare and contrast the diagnoses of the two methods. It was found that Raman spectroscopy can detect MSUM and CPPD crystals with good sensitivity and specificity at concentrations as low as 5 microg/mL and 2.5 microg/mL, respectively, using the current method. This detection limit of Raman analysis is lower than that reported for PLM. Raman and PLM diagnoses of clinical samples agreed in 32 out of 35 samples in the entire sample pool. However, the rate of disagreement between PLM-based and Raman-based diagnoses was noteworthy within the subset of diseased samples (3 out of 10), indicating that PLM has limitations and that the confirmation by a secondary method is essential for a reliable outcome. The proposed protocol of sample preparation and Raman analysis ascribes baseline feasibility to the diagnosis of gout and pseudogout by Raman spectroscopy, thus justifying further studies using a larger clinical sample set for obtaining sensitivity and specificity.