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Aim: The present study aimed to investigate the relationship between delirium and tryptophan and its metabolites in critically ill older patients. Methods: This prospective and observational study was conducted on patients who were > 60 years of age and hospitalized for at least 24 h at the internal medicine ICU in the tertiary health care unit (n = 120). All consecutively selected patients were evaluated for delirium at the baseline and follow-up period at the bedside by an intensive care specialist. At the end of the 24 h follow up, the patients were divided into two groups (with and without delirium). Clinical properties and tryptophan (TRP) and its metabolites [kynurenine (KYN), kynurenic acid (KYNA), quinolinic acid (QA), 3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid (3HAA)] were compared between groups. Results: The median age of the patients was 79.5 (62–95) years and 53.3% were female. The median age and CCI score were significantly higher among patients with delirium than in those without delirium (P = 0.001 and 0.031, respectively). The level of TRP was significantly (borderline) decreased among patients with delirium (P = 0.056). The KYN/TRP and QA/TRP ratios were statistically and significantly higher in patients with delirium than those without (P < 0.001 and P = 0.016, respectively). The best predictive values for detecting delirium were calculated as ≤ 14,100 ng/mL for TRP (AUC: 0.601, P = 0.052), > 1.12 for KYN/TRP ratio (AUC: 0.704, P < 0.001), and > 0.75 for QA/TRP ratio (AUC: 0.627, P = 0.013). The QA/TRP ratio showed independent and borderline significant association with being delirium in multivariable regression analysis (Odds ratio: 2.007, P = 0.066). Conclusion: This study demonstrated that tryptophan and its metabolites obtained within the first 24 h of ICU admission might have predictive value for determining high-risk older patients for delirium.

Objectives: Vitamin D is one of the major hormones involved in the metabolism of calcium (Ca) and phosphorus (P). In the present study, we aimed to determine the analytical performance of the immunoassay method used for determining plasma 25-hydroxyvitamin D [25(OH)D] levels in routine clinical practice in laboratories. Methods: Venous blood samples were collected from 156 patients for the comparisons and were analyzed with Siemens ADVIA Centaur XPT, the Roche Cobas 6,000’s module e601, Abbott Architect i2000, and the liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results: The four methods were analyzed and compared through the Passing-Bablok regression for 25(OH)D, and the highest correlation was found at LC-MS/MS and Cobas 6,000’s module e601 (r=0.799), LC-MS/MS/Abbott Architect i2000, and LC-MS/MS/Siemens ADVIA Centaur XPT as r=0.736, 0.721, respectively. The correlation coefficient was found between Abbott Architect i2000 with Roche Cobas e601 and Siemens ADVIA Centaur XPT as r=0.934 and r=0.907, respectively. Also, the correlation coefficient was found between Roche Cobas e601 and Siemens ADVIA Centaur XPT as r=0.906. Conclusions: The Roche Cobas assay showed better performance, compared with the other assays. Based on our findings, the chemiluminescence methods in automated systems seem to be expedient.