The effectiveness of the sarcopenia index in predicting septic shock and death in elderly patients with community-acquired pneumonia

BACKGROUND: Community-acquired pneumonia (CAP) causes high morbidity and mortality in all age groups worldwide. Lower muscle radiodensity was associated with worse clinical outcomes (including shock) and higher in-hospital mortality. Prompt detection of sarcopenia in older adults with CAP is important. The measurement of muscle mass often involves specialized and expensive techniques. A relatively simple and inexpensive method such as the sarcopenia index (SI) to measure muscle mass would be helpful. Therefore, we performed a retrospective cohort study to assess the association between SI and septic shock risk and mortality in older patients with CAP. STUDY DESIGN: In this retrospective cohort study, information on hospitalized CAP patients, including general information and septic shock, were obtained from the medical record database of the Southwest Medical University Zigong Affiliated Hospital, China. Data on patient survival and mortality (all-cause) were acquired from government authorities and telephonic follow-up. Serum creatinine (Cr) and cystatin-C (CysC) levels on admission were included in the database. The SI was determined as the serum Cr/CysC ratio × 100 and the participants were assigned to low and high SI groups. The association between SI and septic shock was evaluated by logistic regression, and that between SI and mortality by Cox regression analysis. RESULTS: In total, 769 older adults (≥ 60 years) with CAP were included, of which 480(62.4%) were male and 289(37.6%)were female. We found that the total prevalence of septic shock in older adults with CAP was 16.0%. In the female group, septic shock was more prevalent in the low SI group than in the high SI group (low SI vs. high SI, 22.22% vs. 11.52%, p = 0.024). Following adjustment for confounders, there was a significant association between high SI and a lower risk of septic shock in female patients (OR = 0.38, 95%CI: 0.16–0.94; p < 0.05). The total death toll of older adults with CAP was 332(43.2%). Irrespective of sex, there was a higher risk of mortality in the low SI group (total group: low SI vs. high SI, 63.02% vs. 36.57%, p < 0.001; male group: low SI vs. high SI, 63.03% vs. 39.34%, p < 0.001; female group: low SI vs. high SI, 73.61% vs. 28.57%, p < 0.001) and, after adjustment for confounding factors and irrespective of sex, high SI was a protective factor for mortality in older adults with CAP (total group: HR = 0.64, 95%CI: 0.48–0.84; p < 0.05; male: HR = 0.69, 95%CI: 0.49–0.97; p < 0.05; female: HR = 0.39, 95%CI: 0.24–0.62; p < 0.05). CONCLUSION: While the SI effectively predicts mortality in older adults with CAP, it was only found to be associated with septic shock in older females.