A total of 11941(70.5%) patients with PIN were enrolled, while 3327(19.7%) patients with UTI, 1053 (6.2%) patients with ITI, and 602 (3.6%) patients with SSI were collected to be used as controls. The initial cohort included 16923 patients (Fig. 1), and the baseline characteristics are presented in Table 1. The incidence of thrombocytopenia were 9.8% (PIN), 6.4% (UTI), 5.0% (ITI) and 5.1% (SSI).
Patients with PIN showed a higher incidence of thrombocytopenia than patients with other infectious diseases
For all subjects with infectious disease, factors associated with thrombocytopenia by logistic analysis are shown in Table 2. By univariate analysis, sex, hypertension comorbidity and different infection sites were associated with thrombocytopenia. In multivariate analysis, after adjusting for the sex and hypertension comorbidity confounders, patients with other organ infections presented a lower incidence of thrombocytopenia than PIN patients did(UTI OR=0.61, 95% CI: 0.52-0.71; ITI OR=0.48, 95% CI: 0.33-0.69; SSI OR=0.46, 95% CI: 0.35-0.61; all P<0.001), which indicates that patients with PIN are more likely to develop thrombocytopenia than patients with one of three other infections.
PIN patients with RF comorbidityhad a relatively high risk for thrombocytopenia
To explore the risk factors for thrombocytopenia in PIN patients, factors influencing thrombocytopenia were identified by logistic analysis (Table 3). The CPIS was evaluated to assess the severity of PIN. Univariate analysis showed that the higher CPIS was (OR=1.25, 95% CI: 1.18–1.32; P<0.001), the higher the risk of thrombocytopenia. RF (OR=1.68, 95% CI: 1.35–2.09; P<0.001) and hypertension (OR=0.73, 95% CI: 0.65-0.83; P<0.001) were associated with thrombocytopenia. Multivariate analysis showed that hypertension was a positive factor for thrombocytopenia (OR=0.74, 95% CI: 0.65–0.85; P<0.001). RF (OR = 1.59, 95% CI: 1.27–1.98; P<0·001) and a high CPIS (OR=1.24, 95% CI: 1.17–1.31; P<0.001) were risk factors for thrombocytopenia. Interestingly, patients with RF appeared more prone to thrombocytopenia than those without RF.
Low PaO2 was a key risk factor for thrombocytopenia
To explore the key effective factor in PIN patients with RF, a subgroup analysis was conducted and the result is shown in Table 4. The APACHE II scoring system was adopted here to estimate the severity of RF . Univariate analysis showed that the higher the APACHE II score was (OR=1.09, 95% CI: 1.02–1.15; P=0.007), the higher the risk of thrombocytopenia was. Relatively low PaO2 (OR=0.88, 95% CI: 0.85–0.91; P<0.001), hypertension (OR = 0.64, 95% CI: 0.41–0.99; P=0.046) and COPD (OR=2.35, 95% CI: 1.22–4.53; P=0.01) were associated with thrombocytopenia. In multivariate analysis, both COPD (OR = 2.40, 95% CI: 1.22–4.76; P=0.01) and a high APACHE II score (OR=1.06, 95% CI: 1.01–1.13; P=0.03) were risk factors for thrombocytopenia. It was important to emphasize that low PaO2 was a potential risk factor for thrombocytopenia, which was supported by result of relatively high PaO2 associated with a relatively low risk of thrombocytopenia (OR=0.88, 95% CI: 0.85–0.92; P<0.001). There was no difference in the distribution of PaO2 among different pathogen groups (P=0.11) (Supplementary Fig. 1). Likewise, pathogens weren’t associated with thrombocytopenia in PIN patients with RF (all P>0.05) (Supplementary Table 1).
Hypoxic mouse models with low PaO2
To verify whether low PaO2 is a risk factor for thrombocytopenia, hypoxic mouse models were constructed to analyze the blood gas content in left ventricular blood. The results showed that the PaO2 (mmHg) decreased significantly in blood from hypoxic mice(n=8) compared with that from normoxic mice (59.63±6.39 vs. 76.63±9.58, respectively; P<0.05). For each Comparation, the sample size was eight.
Reduction in PLTs independent of platelet activation after hypoxia
The count of PLTs (×109/L) in angular vein blood decreased in hypoxic mice compared with that of normoxic mice (518.38±127.92 vs. 840.75±77.30, respectively; P<0.05) and accompanied by increased hemoglobin (HGB) level (g/L) (196.0±10.56 vs. 140.0±5.78, respectively; P<0.05). There was no difference in the plasma soluble P-selectin concentration(ng/ml) between these two groups (77.55±5.38 vs. 74.86±7.85, respectively; P>0.05). For each comparation, the sample size was eight.
MK numbers decreased in hematopoietic organs after hypoxia
To explore the possible reason for thrombocytopenia after hypoxia treatment, we investigated the amount of megakaryocytes in hematopoietic organs including lung, marrow and spleen. The results of flow cytometry analysis showed lower proportions of CD41-positive cells (%) in lungs (6.09 [5.66–6.71] vs. 8.82 [8.26–10.27], respectively; P<0.05, Fig. 2 A-B), bone marrow (2.11±1.12 vs. 5.03±1.72, respectively; P<0.05, Fig. 2 C-D) and spleen (0.39 [0.36–0.59] vs. 0.74 [0.66–1.03], respectively; P<0.05, Fig. 2 E-F) in hypoxic mice than in normoxic mice. Consistent with the flow cytometry results, the counts of CD41-positive cells calculated by fluorescence microscopy in lungs (39.0±5.35 vs. 54.25±12.87, respectively; P<0.05, Fig. 3 A-B), bone marrow (10.00±2.78 vs. 24.88±3.68, respectively; P<0.05, Supplementary Fig. 2 A-B) and spleen (2.75±1.04 vs. 8.75±5.29, respectively; P<0.05, Supplementary Fig. 3 A-B) in hypoxic mice were lower than those in normoxic mice. These results suggested that the reduction of megakaryocytes in the three hematopoietic organs after hypoxia might be part of the reason for thrombocytopenia. We speculate a perturbed PLT production in lung with the effect of hypoxia.
Impaired platelet production was observed in hypoxic mouse lungs
To determine the number of platelets produced in lungs, we investigated the PLTpre and the PLTpost. The result showed that ere allesult of flow cytometry patients with a than painfectious disease was compared, al os abundant, clinical studies address. the PLTpost was higher than the PLTpre in the normoxic group (713.63±124.15 vs. 543.75±121.17, respectively; P<0.05), which indicated that thrombopoiesis occured in lungs. However, this phenomenon was not obvious in hypoxic mice (339.63±95.47 vs. 391.13±117.30, respectively; P>0.05). Namely, the △PLTpost-pre value was less significant in the hypoxic group than in the normoxic group (F=25.47, P<0.05). For each Comparation, the sample size was eight.