Associations between air pollutants and acute exacerbation of drug-resistant tuberculosis: evidence from a prospective cohort study.

BACKGROUND: Short-term exposure to air pollution may trigger symptoms of drug-resistant tuberculosis (DR-TB) through stimulating lung tissue, damaging tracheobronchial mucosa, the key anti-mycobacterium T cell immune function, and production and release of inflammatory cytokines. OBJECTIVE: To investigate the association between acute exacerbations of DR-TB and short-term residential exposure to air pollutants (PM10, PM2.5, SO2, NO2, CO and O3) based on a large prospective cohort in Anhui Province, China. METHOD: Patients were derived from a prospective cohort study of DR-TB in Anhui Province. All DR-TB patients underwent drug-susceptibility testing and prefecture-level reference laboratories confirmed their microbiologies. The case-crossover design was performed to evaluate the association between the risk of acute exacerbations of DR-TB and short-term residential exposure to air pollution. RESULTS: Short-term NO2 exposure was significantly related to an elevated risk of first-time outpatient visit due to acute exacerbations of DR-TB(relative risk:1.159, 95% confidence interval:1.011 ~ 1.329). Stratification analyses revealed that the relationship between the risk of acute exacerbations and NO2 exposure was stronger in the elderly (age ≥ 65) DR-TB patients, and in individuals with a history of TB treatment. CONCLUSIONS: NO2 Exposure was significantly associated with an elevated risk of acute exacerbation of DR-TB in Anhui Province, China.

Serum albumin mediates the associations between heavy metals and two novel systemic inflammation indexes among U.S. adults.

BACKGROUND: The effects of heavy metal exposure on immunological function have sparked widespread concern, but unequivocal evidence on the association between mixed metal exposure and novel systemic inflammatory indexes remains scarce. OBJECTIVES: This study aimed to analyze the associations of heavy metals with two novel systemic inflammation indexes and the mediated effects of serum albumin. METHODS: Nineteen metals were detected among 4082 U.S. adults based on the NHANES. A linear regression, restricted cubic splines (RCS) regression, weighted quantile sum (WQS), Quantile-based Gcomputation (qgcomp), and Bayesian kernel machine regression (BKMR) were conducted to evaluate the associations of single metal and mixed metals with systemic immune-inflammation index (SII) and systemic inflammation response index (SIRI) levels, respectively. A series of subgroup analyses were used to identify potentially vulnerable populations. Furthermore, we conducted mediation analyses to investigate the mediated effects of serum albumin on the associations of metals with SII and SIRI. RESULTS: In the single-exposure model, exposure to various metals such as urinary Co, As, and serum Zn, Cu was associated with SII and SIRI (PFDR<0.05). Simultaneously, the above metals were linear positively correlated with SII and SIRI. Mixed-exposure analyses consistently showed that overall mixed urinary metal levels were positively pertinent for SII and SIRI levels, and the metal Co played a significant role in the urinary metal mixtures. Subgroup analyses showed that exposure to urinary Cd in men and elderly people increased SII and SIRI levels. The results of mediation analyses suggested the association of urinary metal mixture with SII and SIRI was mediated by albumin, and the proportion of mediation was 14.45% and 9.49%, respectively. CONCLUSIONS: Our findings suggested that metal exposure is strongly associated with the levels of system inflammation indexes and that serum albumin is, in part, a mediator of this association.

Increased circulating sclerostin levels in rheumatoid arthritis patients: an updated meta-analysis.

BACKGROUND: Sclerostin, a regulator of bone metabolism and vascular calcification involved in regulating the Wnt/ß-catenin signaling pathway, has been shown to be involved in the pathogenesis of rheumatoid arthritis (RA). However, current results regarding the circulating sclerostin level of RA patients are debatable. This study aimed to evaluate the circulating level of sclerostin in RA patients and briefly summarize its role. METHOD: PubMed, EMBASE, and the Cochrane Library databases were systematically searched till May 27, 2021, for eligible articles. Useful data from all qualified papers were systematically extracted and analyzed using Stata 12.0 software (Stata Corp LP, College Station, TX, USA). RESULTS: Overall, 13 qualifying studies including 1030 cases and 561 normal controls were analyzed in this updated meta-analysis. Forest plot of this meta-analysis showed that RA patients had higher circulating sclerostin levels (P < 0.001, standardized mean difference [SMD] = 0.916, 95% CI: 0.235-1.597) compared to normal controls. Subgroup analyses implied that age, region, and assay method were associated with sclerostin level in RA patients. CONCLUSION: RA patients have higher circulating sclerostin levels, and these was influenced by age, region, and assay method.

Association of PER2 gene single nucleotide polymorphisms with genetic susceptibility to systemic lupus erythematosus.

The circadian clock plays a crucial role in the progress of systemic lupus erythematosus (SLE). In this study, we performed a case-control study to explore the association between Period 2 (PER2) gene single nucleotide polymorphisms (SNPs) and the susceptibility of systemic lupus erythematosus (SLE). A total of 492 SLE patients and 493 healthy controls were included. The improved multiple ligase detection reaction (iMLDR) was used for genotyping. The correlations between four SNPs of PER2 (rs10929273, rs11894491, rs36124720, rs934945) and the genetic susceptibility and clinical manifestations of SLE were analyzed. Significant differences were observed in the distributions of allele frequencies and genotype under dominant model in rs11894491 between SLE patients and controls (p = 0.030, p = 022, respectively). We hypothesized that PER2 gene SNPs was related to the genetic susceptibility and clinical manifestations, implying the potential role of PER2 in the pathogenesis of SLE.

Decreased Expression of Semaphorin 3A and Semaphorin 7A Levels and Its Association with Systemic Lupus Erythematosus.

A growing body of data suggests that semaphorins are involved in both normal and pathological immune responses, as well as autoimmune pathologies. To investigate the plasma semaphorin 3A (Sema3A) and semaphorin 7A (Sema7A) levels in systemic lupus erythematosus (SLE) patients and their correlation with clinical manifestations and laboratory indexes, a two-step method was applied. First, 80 SLE patients and 80 healthy controls were recruited for comparing serum Sema3A and Sema7A concentrations. Second, 40 rheumatoid arthritis (RA) patients and 40 sjögren's syndrome (SS) patients were then included as disease controls. Plasma Sema3A and Sema7A concentrations were detected by ELISA. There were significant differences in Sema3A and Sema7A among four groups. When compared to healthy controls, both Sema3A and Sema7A levels were decreased in SLE and increased in RA; increased Sema3A level and decreased Sema7A level were found in SS. There were significant differences in Sema3A concentration between SLE and RA, SLE and SS. Moreover, there were significant differences in Sema7A level between SLE and RA, SS and RA. However, no significant differences in Sema3A between SS and RA and no significant differences in Sema7A between SS and SLE were observed. Both plasma Sema3A and Sema7A levels were correlated with anti-SSA and IgM. Area under curve (AUC) of the receiver operating characteristic (ROC) curve for Sema3A and Sema7A were 0.535 (0.455-0.613) and 0.671 (0.594-0.742), respectively. Aberrant Sema3A and Sema7A expression and their clinical associations in SLE suggest their important role in this disease.

Elevated Circulating Interleukin-17 Levels in Patients with Systemic Lupus Erythematosus: A Meta-analysis.

BACKGROUND: Previous studies concerning the circulating interleukin-17 (IL-17) in systemic lupus erythematosus (SLE) were contradictory. AIMS: To further precisely investigate circulating IL-17 in SLE and evaluate its influential factors by meta-analysis. METHODS: EMBASE, PubMed and Cochrane Library were comprehensively searched to obtain studies on circulating IL-17 in SLE patients by November 22, 2018. The results were illustrated by pooled standard mean difference (SMD) with corresponding 95% confidence interval (CI) using random-effects model as there was significant heterogeneity, which was estimated using Cochran Q and I2 statistics. Subgroup analyses and sensitivity analyses were also conducted. RESULTS: Overall, 1872 articles were reviewed and 20 studies involving 1067 subjects with SLE and 721 healthy controls (HCs) were enrolled in the final analysis according to inclusion criteria. Compared with HCs, circulating IL-17 levels in SLE patients were elevated (SMD: 1.183, 95% CI: 0.763-1.603; P < .001). Moreover, in comparison to HCs, European and Asian SLE patients, age <30 years, disease duration ≥5 years, NOS scores <7 and using ELISA showed increased circulating IL-17 status, whereas no significant change was observed in other subgroups. There was no significant publication bias. Sensitivity analyses demonstrated that the results of our meta-analysis were robust. CONCLUSIONS: SLE patients have higher circulating IL-17 levels, which is influenced by ethnic, age and disease duration, literature quality and measurements.

Seasonality and global public interest in psoriasis: an infodemiology study.

OBJECTIVE: Although patients with psoriasis frequently report seasonal changes in their symptoms, the seasonality of psoriasis has rarely been explored. This study aims to investigate the seasonal pattern of and global public interest in psoriasis using Google search data. METHODS: Internet search data were collected from Google Trends. Data on the relative search volume (RSV) from January 2004 to December 2018 were retrieved using the term psoriasis. Cosinor analyses were conducted to examine the seasonality of psoriasis using data from two southern hemisphere countries (Australia and New Zealand) and four northern hemisphere countries (USA, Canada, UK and Ireland). RESULTS: Overall, searches for psoriasis steadily decreased between 2004 and 2010, and then rose from 2011 to 2018. On cosinor analyses, RSV of 'psoriasis' displayed a significant seasonal variation worldwide (p<0.025). Further analyses confirmed the seasonality of psoriasis-related RSV in Australia, New Zealand, USA, Canada, UK and Ireland (p<0.025 for all), with peaks in the late winter/early spring months and troughs in the late summer/early autumn months. The top 11 rising topics were calcipotriol/betamethasone dipropionate, ustekinumab, apremilast, shampoo, eczema, guttate psoriasis, seborrhoeic dermatitis, dermatitis, psoriatic arthritis, atopic dermatitis and arthritis. CONCLUSION: There was a significant seasonal pattern for psoriasis, with peaks in the late winter/early spring and troughs in the late summer/early autumn. Further studies are warranted to confirm the seasonal pattern of psoriasis using clinical data and to explore the underlying mechanisms.

Elevated circulating asymmetric dimethylarginine levels in rheumatoid arthritis: a systematic review and meta-analysis.

Rheumatoid arthritis (RA) patients have increased risk of cardiovascular disease (CVD) death. Elevated asymmetric dimethylarginine (ADMA) levels have been reported to be an independent predictor of CVD morbidity and mortality, however, the role of ADMA in RA remains undetermined. To derive a more accurate estimation on circulating ADMA levels in RA patients, a meta-analysis was performed. Embase, PubMed, and The Cochrane Library database (up to October 7 2018) were used to acquire published literatures. Heterogeneity test was performed by the Q statistic and quantified using I2. Publication bias was evaluated using a funnel plot and Egger's linear regression test. A total of 174 articles were identified, 16 studies with 1365 subjects (666 RA patients and 699 healthy individuals) were ultimately included. Plasma/serum ADMA levels appeared to be higher in RA patients than healthy controls (SMD = 0.84, 95% CI 0.32, 1.35). By assessing the BMI, age, disease duration and disease activity as subgroups, BMI ≥ 24 and BMI < 24 groups both showed elevated ADMA levels than controls, disease duration ≥ 8, age < 50 and disease activity ≥ 3.2 and < 5.1 group had a higher ADMA level than control groups. However, disease duration < 8, disease activity ≥ 5.1 and age ≥ 50 groups showed no difference between two groups. Circulating ADMA levels are higher in RA patients compared with healthy controls. In addition, ADMA levels are influenced by age, disease duration and disease activity.

Circulating Levels of Osteoprotegerin, Osteocalcin and Osteopontin in Patients with Rheumatoid Arthritis: A Systematic Review and Meta-Analysis.

OBJECTIVE: Currently published data regarding the potential role of osteoprotegerin (OPG), osteocalcin (OCN) and osteopontin (OPN) for the discrimination between rheumatoid arthritis (RA) and osteoarthritis (OA) are contradictory. To derive a more precise evaluation, a meta-analysis was performed. METHODS: Published literatures comparing plasma/serum OPG, OCN and OPN levels between RA group and OA controls were searched in PubMed, Embase and the Cochrane Library. The Newcastle-Ottawa Scale was used to assess the study quality. Pooled standard mean difference (SMD) with 95% confidence interval (CI) was calculated by random-effect model analysis. Heterogeneity test was performed by the Q statistic and quantified using I2. RESULTS: Nine studies including 438 RA patients and 255 OA patients were finally incorporated in the meta-analysis after examining title, type, abstracts and full text. The results showed that RA patients had higher plasma/serum OPN (pooled SMD = -2.57, 95% CI = -4.72 to -0.41) levels when compared to OA patients. No significant difference in plasma/serum OPG (pooled SMD = -0.29, 95% CI = -1.07‒0.49) and OCN (pooled SMD = -0.09, 95% CI = -0.48‒0.31) levels were found between RA patients and OA patients. Subgroup analysis indicated that plasma/serum OPG levels had no significant differences between RA patients and OA patients in Europe and Asian. CONCLUSIONS: Overall, there is no significant difference in circulating OPG and OCN levels between RA patients and OA patients. However, plasma/serum OPN level is significantly higher in RA patients compared with OA patients.

Leveraging Google Trends to investigate the global public interest in rheumatoid arthritis.

This study aims to investigate the global public interest in rheumatoid arthritis by evaluating search term popularity changes of the disease over a decade. Google Trends was applied to retrieve search popularity scores for the term 'rheumatoid arthritis' between January 2004 and December 2017, utilizing the category of "health". Overall, relative searches volume for rheumatoid arthritis steadily decreased from January 2004 to December 2010, and then slowly rose from January 2011 to December 2017. There were significant seasonal variations in relative searches volume for the term 'rheumatoid arthritis' (Amplitude = 3.11; Phase: Month = 4.3; Low point: Month = 10.3; p < 0.025). Relative searches volume peaked in April and reached the lowest level in October. The top 11 rising topics were scleroderma, Anna Marchesini, C-reaction protein, osteoarthritis, arthritis, joint pain, autoimmune disease, rheumatoid factor, rheumatology, methotrexate, and systemic lupus erythematosus, ranking from high to low by relative growth of topic regarding rheumatoid arthritis. In conclusion, the evidence from Google Trends analysis demonstrates a significant seasonal variation in rheumatoid arthritis, with a peak in April. In addition, the top rising search queries are beneficial for physicians to search the Internet themselves for websites that provide high-quality information to recommend to their patients.

Lack of association between mean platelet volume and disease activity in systemic lupus erythematosus patients: a systematic review and meta-analysis.

Currently, many studies have focused on the possibility of using mean platelet volume (MPV) as a biomarker for disease activity in patients with systemic lupus erythematosus (SLE). To derive a more accurate estimation, a meta-analysis was conducted. Embase, PubMed, The Cochrane Library database and several Chinese databases (up to Nov 1 2017) were used to acquire published literatures on association of MPV levels with disease activity in SLE patients. Fixed-effects or random-effect model analysis was performed to calculate pooled standard mean difference (SMD) with 95% confidence interval (CI). Heterogeneity test was tested by the Q statistic and quantified using I2. A funnel plot and Egger's linear regression test were used to evaluate the potential publication bias. A total of 618 articles were identified, nine studies with 376 active SLE patients and 270 inactive SLE patients were finally included. No significant difference in MPV level was found between active SLE patients and inactive SLE patients (SMD = - 0.05, 95% CI: - 0.83, 0.73). Subgroup analyses stratified by age or region also demonstrated consistent results. No significant publication bias was observed (P > 0.05). The sensitivity analysis showed no significant change when any one study was excluded. In summary, our meta-analysis does not support the use of MPV as an indicator for monitoring disease activity in SLE patients. Further longitudinal studies with larger sample size are warranted to unveil the possibility of using MPV as a biomarker of disease activity.

Hormonal and reproductive factors in relation to the risk of rheumatoid arthritis in women: a prospective cohort study with 223 526 participants.

OBJECTIVE: This study aimed to examine rheumatoid arthritis (RA) risk associated with hormonal and reproductive factors in women from the large cohort of the UK Biobank. METHODS: Data on hormonal and reproductive factors in women were collected from a prospective cohort of 223 526 UK Biobank participants. The potential relationship between reproductive factors and RA risk was assessed using restricted cubic spline. Hazard ratios (HR) were estimated using Cox proportional hazard regressions. RESULTS: During a median follow-up of 12.39 years, 3313 women with RA were identified. Age at menarche >14 years was associated with a greater RA risk (HR 1.13, 95% CI 1.02 to 1.26) compared with menarche at 13. The multiple adjusted HR for RA in women with menopause at <45 years was 1.46. Reproductive years <33 increased the risk of RA (HR 1.39, 95% CI 1.21 to 1.59). Compared with those with 2 children, women with ≥4 children were associated with a higher risk of RA (HR 1.18, 95% CI 1.04 to 1.34). Women who had a hysterectomy (HR 1.40, 95% CI 1.25 to 1.56) or oophorectomy (HR 1.21, 95% CI 1.08 to 1.35) had a higher risk of RA than those without a hysterectomy or oophorectomy. Both hormone replacement therapy (HRT) use (HR 1.46, 95% CI 1.35 to 1.57) and HRT duration (HR 1.02, 95% CI 1.01 to 1.03) were associated with a higher risk of RA. CONCLUSIONS: Some hormonal and reproductive factors were associated with a higher risk of RA. Hormonal and reproductive factors should be considered in risk assessment and formulating management plans in female patients with RA.

MicroRNAs as Key Regulators in RA and SLE: Insights into Biological Functions.

MicroRNAs (miRNAs) are non-coding RNA molecules that bind to mRNAs to regulate gene expression. Since changes in miRNA expression levels have been found in a variety of autoimmune illnesses, miRNAs are important in autoimmune diseases. MiRNAs serve not only as pathogenic factors and biomarkers for autoimmune diseases but also as important targets for disease therapeutics. Although miRNA-based treatments are still in the research stage, in-depth investigations into the biological functions of miRNAs have significantly enhanced our understanding of their mechanisms in autoimmune diseases. The purpose of this review is to summarize the biological functions of miRNAs, their roles in rheumatoid arthritis and systemic lupus erythematosus, therapeutic strategies, and challenges.

Impact of short-term exposure to ambient air pollution on osteoarthritis: a multi-city time-series analysis in Central-Eastern China.

Osteoarthritis (OA) is a threat to public health issue with high morbidity and disability worldwide. However, unequivocal evidence on the link between air pollution and OA remains little, especially in multi-study sites. This study aimed to explore the relationship between short-term exposure to main air pollutants and the risk of OA outpatient visits in multi-study sites. A multi-city time-series analysis was performed in Anhui Province, Central-Eastern China from January 1, 2015, to December 31, 2020. We used a two-stage analysis to assess the association between air pollution and daily OA outpatient visits. City-specific associations were estimated with a distributed lag nonlinear model and then pooled by random-effects or fixed-effects meta-analysis. Stratified analysis was conducted by gender, age, and season. Additionally, the disease burden of OA attributable to air pollutant exposure was calculated. A total of 35,700 OA outpatients were included during the study period. The pooled exposure-response curves showed that PM2.5 and PM10 concentrations below the reference values could increase the risk of OA outpatient visits. Concretely, per 10 ug/m3 increase in PM2.5 concentration was linked to an elevated risk of OA outpatient visits at lag 2 and lag 3 days, where the effect reached its highest value on lag 2 day (RR: 1.023, 95%CI: 1.005-1.041). We observed that a 10 µg/m3 increase in PM10 was positively correlated with OA outpatient visits (lag2 day, RR: 1.011, 95%CI: 1.001-1.025). Nevertheless, no statistical significance was discovered in gaseous pollutants (including SO2, O3, and CO). Additionally, a significant difference was found between cold and warm seasons, but not between different genders or age groups. This study reveals that particulate matter is an important factor for the onset of OA in Anhui Province, China. However, there is no evidence of a relationship of gaseous pollutants with OA in this area.

Association between traffic-related air pollution and hospital readmissions for rheumatoid arthritis in Hefei, China: A time-series study.

Air pollution is an important risk factor for autoimmune diseases, but its association with the recurrence of rheumatoid arthritis (RA) remains unclear so far. This study aimed to investigate the short-term association between traffic-related air pollutants and hospital readmissions for RA in Hefei, China. Data on daily hospital readmissions for RA and traffic-related air pollutants, including particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), and carbon monoxide (CO), from 2014 to 2018 were retrieved. A time-series approach using generalized linear regression model was employed. The analysis was further stratified by sex, age and season. A total of 1153 readmissions for RA were reported during the study period. A significant association between high-concentration PM2.5 (90th percentile) and RA readmissions was observed on lag1 (relative risk (RR) = 1.09, 95% confidence interval (CI): 1.01-1.19) and lasted until lag3 (RR = 1.06, 95%CI: 1.01-1.12). From lag2 to lag5, high-concentration NO2 (90th percentile) was associated with increased risk of RA readmissions, with the highest RR observed at lag 4 (1.11, 95%CI: 1.05-1.17). Stratified analyses indicated that females and the elderly appeared to be more vulnerable to high-concentration PM2.5 and NO2 exposure. High-concentration PM2.5 and NO2 in cold seasons were consistently significantly associated with increased risk of RA readmissions. Exposure to high-concentration PM2.5 and NO2 was associated with increased risk of RA readmissions. Protective measures against the exposure to high-concentration PM2.5 and NO2 should be taken to reduce the recurrence risk in RA patients, especially in females, the elderly and during cold seasons.

Low ambient temperature increases hospital re-admissions for systemic lupus erythematosus in humid subtropical region: a time series study.

Currently, the correlation between ambient temperature and systemic lupus erythematosus (SLE) hospital admissions remains not determined. The aim of this study was to explore the correlation between ambient temperature and SLE hospital admissions in Hefei City, China. An ecological study design was adopted. Daily data on SLE hospital admissions in Hefei City, from January 1, 2007, to December 31, 2017, were obtained from the two largest tertiary hospitals in Hefei, and the daily meteorological data at the same period were retrieved from China Meteorological Data Network. The generalized additive model (GAM) combined with distributed lag nonlinear model (DLNM) with Poisson link was applied to evaluate the influence of ambient temperature on SLE hospital admissions after controlling for potential confounding factors, including seasonality, relative humidity, day of week, and long-term trend. There were 1658 SLE hospital admissions from 2007 to 2017, including 370 first admissions and 1192 re-admissions (there were 96 admissions with admission status not stated). No correlation was observed between ambient temperature and SLE first admissions, but a correlation was found between low ambient temperature and SLE re-admissions (RR: 2.53, 95% CI: 1.11, 5.77) (3.5 °C vs 21 °C). The effect of ambient temperature on SLE re-admissions remained for 2 weeks but disappeared in 3 weeks. Exposure to low ambient temperature may increase hospital re-admissions for SLE, and thus it is important for SLE patients to maintain a warm living environment and avoid exposure to lower ambient temperature.

Association of Midkine and Pleiotrophin Gene Polymorphisms With Systemic Lupus Erythematosus Susceptibility in Chinese Han Population.

In a previous study, we have reported an increased plasma midkine (MK) and pleiotrophin (PTN) concentrations in patients with systemic lupus erythematosus (SLE) and the increase in MK and PTN associated with inflammatory cytokines interleukin (IL)-17 level and some clinical manifestations, suggesting the underlying association of MK and PTN with SLE. This study was conducted to investigate the association between common single-nucleotide polymorphisms (SNPs) in the MK and PTN gene and SLE susceptibility. A total of 989 subjects (496 SLE patients and 493 healthy controls) were included and genotyped for three MK SNPs and seven PTN SNPs in using improved multiple ligase detection reaction (iMLDR). Results have demonstrated no significant differences for genotype and allele frequencies in all 10 SNPs between SLE patients and healthy controls. Case-only analysis in SLE revealed that, in MK gene, the genotype frequency of AA/AG (rs35324223) was significantly lower in patients with photosensitivity than those without; the allele frequency of A/G (rs20542) was significantly higher in patients without serositis. In PTN gene, the A/G allele frequency (rs322236), C/T allele frequency, and TT/CT genotype frequency (rs6970141) showed significantly increased results in patients with immunological disorder compared to those without. Furthermore, no significant differences in plasma MK and PTN concentrations with its SNPs genotypes were found. MK and PTN SNPs showed no associations with SLE genetic susceptibility, but it may be associated with the course of this disease; further studies are needed to focus on the mechanism of MK and PTN genes in the pathogenesis of SLE.

Circulating Meteorin-like Levels in Patients with Type 2 Diabetes Mellitus: A Meta-Analysis.

BACKGROUND: Meteorin-like (Metrnl) is a newly identified adipokine implicated in the pathogenesis of type 2 diabetes mellitus (T2DM), yet data on the circulating levels of Metrnl in patients with T2DM are controversial. To derive a more precise estimation on circulating Metrnl levels in T2DM patients, we conducted this meta-analysis. METHODS: The existing studies on the circulating levels of Metrnl in patients with T2DM published up to 16 January 2020 were comprehensively retrieved from PubMed, Web of Science, EMBASE, and The Cochrane library database. Pooled standard mean difference (SMD) with 95% confidence interval (CI) was calculated using random-effects model. Heterogeneity was assessed and quantified by Cochrane's Q and I2 statistic. All statistical analyses were performed using Stata 12.0 software. RESULTS: Nine studies with 867 T2DM patients and 831 normal glucose tolerance (NGT) controls were included in the final analysis according to the inclusion criteria. No significant difference in circulating Metrnl levels was found between T2DM patients and NGT individuals (pooled SMD = -0.429, 95% CI = -1.077 to 0.219). Compared to controls, circulating Metrnl levels were significantly higher in the subgroups with BMI <25 kg/m2, using plasma sample and patient sample size ≥100, while circulating Metrnl levels were significantly lower in subgroups with age ≤50 years and homeostatic model assessment for insulin resistance (HOMA-IR) ≥4. CONCLUSION: This meta-analysis indicates no significant change in circulating Metrnl levels in T2DM patients. However, this result may be influenced by age, BMI, sample type, HOMA-IR and patients sample size. Further longitudinal studies are warranted to offer more insights into the relationship between Metrnl and T2DM.