[Feasibility of difference between hematocrit and albumin for identifying severity of scrub typhus disease]

To explore the feasibility of difference between hematocrit and albumin (HCT-ALB) to evaluate the severity in patients with severe scrub typhus (Tsutsugamushi disease).

The clinical data of 408 patients with scrub typhus in 37 hospitals located in 15 prefectures of Yunnan Province from January 1st, 2017 to December 31st, 2018 were retrospectively collected. The patients were divided into the non-severe scrub typhus disease group (n = 265) and the severe scrub typhus disease group (n = 143) according to the diagnostic criteria. Volunteers attending Kunming City Medical Center in Yunnan Province for routine physical examination were enrolled as healthy control group (n = 230). HCT, ALB, lactate dehydrogenase (LDH), uric acid (UA), and acute physiology and chronic health evaluations II (APACHE II) and sequential organ failure assessment (SOFA) within 24 hours after admission were collected. HCT-ALB difference was calculated. Pearson method was used to analyze the correlation between HCT-ALB difference and LDH, UA, APACHE II and SOFA scores in patients with severe scrub typhus disease; the receiver operating characteristic (ROC) curve was used to analyze the value of HCT-ALB difference in the diagnosis of severe scrub typhus disease.

(1) There was no significant difference in gender composition between patients with non-severe scrub typhus disease group and severe scrub typhus disease group, but the age of the severe scrub typhus disease group was significantly higher than that of the non-severe scrub typhus disease group (years old: 53.57±15.23 vs. 35.03±23.47, P < 0.01). (2) Compared with the healthy control group, the HCT, ALB of the non-severe scrub typhus disease group and severe scrub typhus disease group were significantly decreased [HCT: (36.54±6.82)%, (38.13±7.60)% vs. (46.20±4.42)%; ALB (g/L): 35.53±5.87, 26.90±6.10 vs. 47.75±4.28, all P < 0.01], and the HCT-ALB difference was significantly increased (5.28±3.90, 11.26±6.62 vs. 1.55±5.32, both P < 0.01). Compared with the non-severe scrub typhus disease group, the HCT of the severe scrub typhus disease group was significantly increased [(38.13±7.60)% vs. (36.54±6.82)%, P < 0.01], the ALB was significantly decreased (g/L: 26.90±6.10 vs. 35.53±5.87, P < 0.01), and the HCT-ALB difference was significantly increased (11.26±6.62 vs. 5.28±3.90, P < 0.01). (3) Pearson correlation analysis showed that HCT-ALB difference was positively correlated with LDH and UA in patients with severe scrub typhus disease (r values were 0.316 and 0.284, respectively, both P < 0.01), and negatively correlated with APACHE II score and SOFA score (r values were -0.229 and -0.198, respectively, both P < 0.05). (4) ROC curve analysis showed that the area under the curve (AUC) of HCT-ALB difference in the diagnosis of severe scrub typhus disease was 0.786, standard error was 0.024, P = 0.000, and 95% confidence interval (95%CI) was 0.739-0.832. When the best diagnostic value was 8.56, the sensitivity was 81.1%, the specificity was 60.8%, and the Youden index was 0.419.

HCT-ALB difference is an indicator to evaluate the severe scrub typhus disease. When HCT-ALB difference is above 8.56, it can be used as an indicator to identify severe scrub typhus disease.