Background Previous studies have investigated the vitamin D status in patients with chronic hepatitis B virus (HBV) infection and its relationship with HBV replication, the results however were inconsistent. The present meta-analysis was carried out to compare the vitamin D levels between patients with chronic hepatitis B (CHB) and healthy controls, and to determine whether vitamin D levels were correlated with HBV viral loads significantly. Methods A systematic search was conducted via PubMed, Web of Science, EMBASE and the Cochrane Library to identify eligible studies until September 28, 2017. We calculated pooled mean difference (MD) and 95% confidence intervals (CI) to quantitatively estimate the difference of vitamin D levels between CHB patients and controls. In addition, correlation between serum vitamin D levels and HBV viral loads was defined by summary correlation coefficient (r value) and the corresponding 95% CI. Results A total of 7 studies involving 814 CHB patients and 696 healthy controls were included. A significantly decreased vitamin D levels was found in CHB patients compared with healthy controls: pooled MD (95% CI) was − 2.03 ng/mL (− 2.60, − 1.46). Latitude-stratified subgroup analysis indicated this difference was more obvious in low latitude areas, with a bigger pooled MD (95% CI) of − 2.72 ng/mL (− 4.57, − 0.87). In addition, we observed an inverse correlation between serum vitamin D levels and HBV viral loads: pooled r (95% CI) was − 0.41(− 0.54, − 0.27). Conclusions Our results showed that vitamin D levels were lower in CHB patients than that of healthy controls and inversely correlated with HBV viral loads, although future comprehensive studies are needed to clarify the underlying mechanisms. Electronic supplementary material The online version of this article (10.1186/s12876-019-1004-2) contains supplementary material, which is available to authorized users.

Acute kidney injury (AKI) in patients with acute‐on‐chronic liver failure (ACLF) is a distinct syndrome to that in patients with cirrhosis, yet is less characterized. The aim of this meta‐analysis was to investigate the impact of AKI on outcome of ACLF. We searched PubMed, Web of Science and Cochrane Library for original articles that evaluated the impact of AKI on outcome of ACLF from 2011 to 2019. Odds ratio (OR) with 95% confidence interval (CI) for 1‐month and 3‐month mortality was calculated. The response rate of vasoconstrictor for hepatorenal syndrome (HRS)‐AKI was assessed. Eight relevant articles with 3610 patients were included. The prevalence of AKI in ACLF patients was 41% (95% CI 32%‐50%). The presence of AKI was significantly associated with 1‐month mortality of ACLF (OR 3.98, 95% CI 3.09‐5.12; P < .001) and 3‐month mortality (OR 4.98, 95% CI 3.59‐6.92; P < .001). Additionally, patients with AKI stage ≥2 showed a higher 3‐month mortality than stage 1 (OR 3.89, 95% CI 2.60‐5.82; P < .001), and those of stage 3 had a higher mortality than stage ≤2 (OR 3.77, 95% CI 2.10‐6.77; P < .001). The pooled response rate of vasoconstrictors was 32% (95% CI 26%‐37%). This meta‐analysis indicated that about 40% of ACLF patients complicated with AKI and the presence of AKI substantially increased the short‐term mortality, together with a poor response rate of vasoconstrictors for HRS‐AKI.