[Analysis of risk factors influencing the detection rate of urate crystal by dual energy computed tomography].

OBJECTIVE: To explore the risk factors of detection of uric acid crystals by dual energy CT (DECT) in patients with gout diagnosed by gold standard. METHODS: From June 2011 to December 2018, clinical data of 29 patients were collected who were diagnosed with acute or chronic gout by positive polarized light analysis of joint synovial fluid in First Hospital of Peking University. Chi-square test, Logistic regression and t-test were used. The relationship between DECT and the clinical data, laboratory examination and drug treatment were analyzed. RESULTS: In this study, 29 patients were included, of whom, 22 patients were detected with uric acid crystals by DECT, and 7 patients were not. According to whether the uric acid crystals were detected or not by DECT, the patients were divided into two groups. Compared with the negative group, the patients were older in positive group [(47±12) vs. (39±11) years, P=0.15], had higher body bass index (BMI) [(27.9±3.7) vs. (22.8±2.1) kg/m2, P=0.002], longer gout disease duration [(135±102) vs.(45±53) months, P=0.035], higher in the highest serum uric acid in history [(643±121) vs. (543±103) µmol/L, P=0.043]. Although uric acid near DECT in positive group was higher than in negative group, there was no statistical difference [(558±150) vs. (513±89) µmol/L, P=0.497]. Comparing positive group with negative group, the percentage of the patients in acute phase was higher than in chronic phase [18(81.8%) vs. 4(57%), P=0.311];the percentage of the patients taking uric-acid-lowering drugs was higher than the other group [22(100%) vs. 5 (71%), P=0.052];the percentage of the patients with recurrent typical attacks was higher than that of those without typical attacks [22 (100%) vs.6 (85%), P=0.241]. The consistency of symptoms and the finding of uric acid crystals by DECT had been compared between the joints. The right knee joint had the highest consistency (Kappa=0.627), followed by the left MTP1 (Kappa=0.58), the right metatarsophalangeal 1(MTP1, Kappa=0.551) and the left knee (Kappa=0.494), all of which had statistical significance. The consistency of the ankle joint was lower (the right ankle joint: Kappa=0.19, the left ankle joint: Kappa=0.256), showing no statistical significance. BMI (kg/m2) [2.307 (1.139-4.670), P=0.02], gout duration (years) [0.306 (0.906-4.881), P=0.186], and the highest uric acid level in history (mg/dL) [0.023 (0.981-2.764), P=0.137] had relationship to the positive result of urate crystals in DECT. CONCLUSION: Gout patients with larger BMI, higher previous highest uric acid value and longer gout duration had higher sensitivity of the positive result in DECT.