The differential diagnosis of lung cancer and pulmonary tuberculosis (PTB) remains challenging because the diseases share clinical manifestations and radiological features, particularly in regions with a high tuberculosis burden. This narrative review evaluates circulating microRNAs (miRNAs), primarily measured in serum, plasma and extracellular-vesicle-enriched fractions, as potential adjunctive biomarkers for this differential diagnosis. The literature search was updated through 3 October 2026. Evidence was synthesized by comparator group, biological matrix, analytical methodology and validation design, distinguishing direct lung cancer–PTB comparisons from disease–control studies and prognostic or monitoring investigations. Numerous miRNAs have been associated with either disease, but shared candidates and opposite expression directions across separate studies do not establish differential diagnostic accuracy. Findings vary with patient selection, sample processing, detection platforms, normalization and reference standards. Direct blood-based comparisons remain limited and report variable discrimination. A plasma panel comprising miR-342-3p, miR-199a-3p and miR-199b-3p differentiated PTB from lung cancer with areas under the curve of 0.911 in training and 0.886 in internal split-sample validation; validation sensitivity and specificity were 87.9% and 75.9%, respectively. Its case–control design, incomplete microbiological confirmation and absence of concomitant lung cancer–PTB assessment limit clinical interpretation. Additional pleural-fluid findings concern a separate matrix and cannot be extrapolated to blood testing. Prognostic and treatment-associated findings remain exploratory and do not establish treatment-guiding or validated monitoring utility. Circulating miRNAs should therefore be considered potential adjuncts to clinical assessment, imaging, microbiological testing and histopathology. Clinical translation requires standardized assays, independent prospective validation in clinically relevant populations, and demonstration of incremental value and clinical utility within existing diagnostic pathways. Future studies should prespecify intended use, assay procedures and diagnostic thresholds, include patients with coexisting disease, and evaluate whether testing improves clinical decisions without replacing established microbiological or tissue confirmation methods.

Background/Objectives: Post-COVID syndrome (PCS) remains a clinically heterogeneous condition. In patients with chronic diseases, real-world evidence is needed to describe its frequency and to identify clinical factors associated with its current presence. This study assessed the prevalence of PCS and factors associated with current PCS status among patients with chronic diseases. Methods: This observational cross-sectional study included a consecutively enrolled source clinical sample of 850 adults receiving inpatient or outpatient care in Almaty and the Almaty Region between June and December 2025. The primary analytic cohort comprised participants with documented prior COVID-19 (n = 250). PCS was assessed at study enrollment according to the national clinical protocol as current symptoms persisting for more than 12 weeks and not explained by an alternative diagnosis. Multivariable logistic regression was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). COVID-19 vaccination was excluded from the primary model and evaluated only in a sensitivity analysis because vaccination timing relative to infection was unavailable. The exploratory association-based probability model was evaluated using the AUC with 95% CI, Brier score, calibration assessment, bootstrap internal validation with 1000 resamples, assessment of age nonlinearity, and decision curve analysis. Results: PCS was identified in 147 of 250 participants with prior COVID-19 (58.8%). In the revised primary multivariable model, age (OR = 1.24 per 10-year increase; 95% CI: 1.01–1.54; p = 0.040) and endocrine diseases (OR = 3.36; 95% CI: 1.69–6.98; p < 0.001) remained associated with current PCS status. The association with endocrine diseases persisted after adjustment for body mass index. The apparent AUC was 0.687 (95% CI: 0.620–0.753), and the Brier score was 0.218. Bootstrap internal validation yielded an optimism-corrected AUC of 0.655, a calibration intercept of 0.061, and a calibration slope of 0.816. Conclusions: PCS was frequent among patients with chronic diseases who had prior COVID-19. Older age and endocrine pathology were the most consistent factors associated with current PCS status. All model-performance estimates were obtained within the development sample; the model should not be used for individual prediction or follow-up planning without prospective external validation.

Background: Depressive symptoms are frequent sequelae of COVID-19 and may remain unrecognized in older outpatients, particularly those with post-COVID syndrome. The objective of the current study was to assess the under-detection of depressive symptoms in older ambulatory patients and to examine its relationship with post-COVID syndrome status. Methods: We conducted an observational outpatient cohort study of adults aged 60–89 years with prior SARS-CoV-2 infection (N = 85), recruited at two city polyclinics. Depressive symptoms were assessed through three detection channels: spontaneous complaint during the visit, a standardized direct question about current depressive symptoms, and the 15-item Geriatric Depression Scale (GDS-15). Agreement between complaint and direct question was evaluated using Cohen’s κ and McNemar’s test. Screening performance of complaint and direct question was assessed against GDS-15 thresholds (≥5; sensitivity analysis ≥ 6). Associations between post-COVID syndrome status and binary depressive-symptom indicators were expressed as risk ratios (RRs). Results: Spontaneous complaints missed a substantial proportion of cases: among complaint-negative patients, 18.3% (15/82) reported depressive symptoms on the direct question (κ = 0.149; McNemar p = 0.00052). Against GDS-15 ≥ 5, complaint sensitivity was 10.3% with specificity 100.0% (F1 = 0.19), whereas the direct question showed higher sensitivity (34.5%) with specificity 87.5% (F1 = 0.43). Using the alternative threshold GDS-15 ≥ 6, complaint sensitivity was 15.0% with specificity 100.0% (F1 = 0.26), and direct question sensitivity was 45.0% with specificity 87.7% (F1 = 0.49). A positive response to the direct question was more frequent in patients with post-COVID syndrome than in controls (RR = 2.70 (1.04–7.00)); stratified estimates suggested higher RRs in patients ≤ 75 years (RR = 4.55 (1.08–19.10)) and in women (RR = 2.67 (1.04–6.83)), with limited precision due to sparse events. Conclusions: In older post-COVID outpatients, reliance on spontaneous complaints leads to marked under-detection of GDS-15 screen-positive depressive symptoms. A standardized direct question improves initial case-finding but does not replace a validated screening scale; a stepped approach (brief direct question followed by a scale when indicated) may be warranted.