{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,25]],"date-time":"2026-06-25T01:48:09Z","timestamp":1782352089173,"version":"3.54.5"},"reference-count":22,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2026,6,24]],"date-time":"2026-06-24T00:00:00Z","timestamp":1782259200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Diagnostics"],"abstract":"<jats:p>Background\/Objectives: Established AECOPD prognostic tools (DECAF, BAP-65, PEARL) predict mortality or readmission rather than length of stay (LOS), and no admission-based instrument specifically targets prolonged hospitalization. We tested whether admission PaCO2 and the Prognostic Nutritional Index (PNI), reflecting ventilatory failure and nutritional\u2013immune reserve, are independently associated with prolonged LOS and examined their interaction. Methods: In this single-center retrospective cohort, 213 adults hospitalized exclusively for AECOPD were analyzed after excluding concomitant pneumonia, pulmonary embolism, decompensated heart failure, and in-hospital deaths. Prolonged hospitalization was pre-specified as LOS &gt; 7 days. Multivariable logistic regression evaluated admission PaCO2 (per +10 mmHg) and PNI (per +5 units) with a PaCO2 \u00d7 PNI interaction; continuous LOS was modeled by Gamma regression. Discrimination was compared with DECAF using DeLong\u2019s test. Results: Prolonged hospitalization occurred in 83 patients (39.0%). Admission PaCO2 was independently associated with prolonged LOS (OR 1.52, 95% CI 1.25\u20131.88; p &lt; 0.001), and PNI showed a borderline association (OR 0.84, 95% CI 0.71\u20131.00; p = 0.049); their interaction was significant but exploratory (OR 1.16, 95% CI 1.02\u20131.32; p = 0.025). In Gamma regression, PaCO2 (RR 1.18 per 10 mmHg) and PNI (RR 0.92 per 5 units) remained associated with LOS. The two-variable model achieved an AUC of 0.682, showing discrimination similar to DECAF in this cohort (AUC 0.695; DeLong p = 0.76), with optimism-corrected AUC 0.672 and calibration slope 0.96. Within moderate hypercapnia (PaCO2 45\u201360 mmHg), the prolonged-LOS rate was 44.4% in low-PNI versus 15.6% in high-PNI patients. Conclusions: In this single-center retrospective cohort of AECOPD patients surviving to discharge, admission PaCO2 and PNI were jointly associated with prolonged hospitalization, reflecting acute ventilatory burden and nutritional\u2013immune reserve. Using only two admission inputs, the framework showed discrimination similar to DECAF without meaningful reclassification gain (IDI \u22120.02; NRI 0.02). Given only moderate discrimination (AUC ~ 0.68), external validation is required before clinical use, with the main practical value likely in complementary stratification within moderate hypercapnia.<\/jats:p>","DOI":"10.3390\/diagnostics16131963","type":"journal-article","created":{"date-parts":[[2026,6,25]],"date-time":"2026-06-25T01:03:56Z","timestamp":1782349436000},"page":"1963","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Hypercapnia, Prognostic Nutritional Index and Length of Stay in Acute Exacerbation of COPD: A Two-Variable Admission Framework"],"prefix":"10.3390","volume":"16","author":[{"given":"Orkun Eray","family":"Terzi","sequence":"first","affiliation":[{"name":"Department of Pulmonology, Bursa Y\u00fcksek \u0130htisas Training and Research Hospital University of Health Sciences, Bursa 16310, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nazl\u0131","family":"\u00c7etin","sequence":"additional","affiliation":[{"name":"Department of Pulmonology, Afyonkarahisar State Hospital, Afyonkarahisar 03100, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B\u00fc\u015fra","family":"Y\u0131ld\u0131r\u0131m Kafal\u0131","sequence":"additional","affiliation":[{"name":"Department of Pulmonology, Bursa Y\u00fcksek \u0130htisas Training and Research Hospital University of Health Sciences, Bursa 16310, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B\u00fc\u015fra","family":"\u00c7omakl\u0131 \u00d6zmen","sequence":"additional","affiliation":[{"name":"Department of Pulmonology, Bursa Y\u00fcksek \u0130htisas Training and Research Hospital University of Health Sciences, Bursa 16310, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"G\u00fclg\u00fcn","family":"\u00c7etinta\u015f Af\u015far","sequence":"additional","affiliation":[{"name":"Department of Pulmonology, Bursa Y\u00fcksek \u0130htisas Training and Research Hospital University of Health Sciences, Bursa 16310, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0073-3506","authenticated-orcid":false,"given":"Seyhan","family":"D\u00fclger","sequence":"additional","affiliation":[{"name":"Department of Pulmonology, Bursa Y\u00fcksek \u0130htisas Training and Research Hospital University of Health Sciences, Bursa 16310, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,6,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"970","DOI":"10.1136\/thoraxjnl-2012-202103","article-title":"The DECAF score: Predicting hospital mortality in exacerbations of chronic obstructive pulmonary disease","volume":"67","author":"Steer","year":"2012","journal-title":"Thorax"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"686","DOI":"10.1136\/thoraxjnl-2016-209298","article-title":"The PEARL score predicts 90-day readmission or death after hospitalisation for acute exacerbation of COPD","volume":"72","author":"Echevarria","year":"2017","journal-title":"Thorax"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1595","DOI":"10.1001\/archinternmed.2009.270","article-title":"Mortality and need for mechanical ventilation in acute exacerbations of chronic obstructive pulmonary disease: Development and validation of a simple risk score","volume":"169","author":"Tabak","year":"2009","journal-title":"Arch. 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