Objectives: This study aimed to compare the clinical, laboratory, and virology profiles of pediatric kidney transplant recipients and immunocompetent children presenting with upper respiratory tract infection, evaluated using multiplex viral polymerase chain reaction panels.
Materials and Methods: This single-center retrospective cohort study included 31 kidney transplant recipients (aged 7-16 years) and 80 age-matched immunocompetent children who presented with upper respiratory tract infection at Başkent University Hospital from January 2023 to March 2025. Demographic, clinical, and laboratory data, including complete blood count, renal and liver function tests, and C-reactive protein, were recorded. Viral pathogens were identified using multiplex polymerase chain reaction. Inflammatory indexes, such as the neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and systemic immune-inflammation index, were calculated. We used SPSS software (version 26.0; IBM) for all statistical analyses, and 2-sided P < .⁰⁵ was considered significant.
Results: A total of 111 pediatric patients with upper respiratory tract infection were included in the study. Kidney transplant recipients were significantly older than patients in the control group without transplant (median 12.0 vs 7.5 years; P < .⁰⁰¹). The neutrophil-to-lymphocyte ratio was higher (P = .⁰⁰¹) and platelet counts were lower (P = .⁰⁰⁴) in the kidney transplant group. Renal (blood urea nitrogen, creatinine, uric acid) and hepatic (aspartate aminotransferase and alanine aminotransferase) parameters were significantly elevated in kidney transplant recipients (all P < .⁰¹). We detected SARS-CoV-2 exclusively in the kidney transplant group (35.5%, P < .⁰⁰¹), whereas other viral agents showed similar distributions between groups. Hospitalization rates and duration of hospital stay did not differ significantly.
Conclusions: Pediatric kidney transplant recipients exhibit distinct inflammatory and biochemical profiles during upper respiratory tract infection compared with healthy peers but show comparable clinical outcomes. Early molecular diagnosis, vigilant monitoring, and preventive strategies such as vaccination remain essential to optimize infection management in this vulnerable population. Key words: Children, Kidney transplantation, Multiplex viral polymerase chain reaction, SARS-CoV-2 infection, Upper respiratory tract infection

Introduction
Patients who have undergone solid-organ transplant are at increased risk for community-acquired respiratory viral infections and tend to experience more severe clinical courses of these infections due to the use of immunosuppression therapy.¹ The incidence of laboratory-confirmed influenza and influenza-related hospitalizations among kidney transplant recipients (KTRs) has been reported to be significantly higher than in the general population.² Immunosuppressive regimens used after solid-organ transplant not only increase susceptibility to infections in children but also weaken the immune response to vaccines. Several studies have demonstrated that both humoral and cellular immune responses to influenza vaccination are markedly reduced in pediatric KTR compared with healthy peers.^3,4 In this context, comparison of the clinical, laboratory, and virology profiles of pediatric KTR presenting with upper respiratory tract infection (URTI) versus the profiles of immunocompetent healthy children with URTI has important clinical value for optimization of infection management and follow-up strategies. This study aimed to compare the frequency of URTI and the associated laboratory parameters between pediatric KTR and healthy control children evaluated using multiplex viral polymerase chain reaction (PCR) panels between 2023 and 2025.

Materials and Methods

Study design and participants
This single-center retrospective cohort study was conducted at Başkent University Hospital, Ankara, Türkiye, from January 2023 to March 2025. Medical data from KTR aged 7 to 16 years were analyzed. During the study period, a total of 31 pediatric KTR who presented with URTI symptoms and underwent multiplex viral PCR testing on nasopharyngeal swab samples were included. During the same period, 80 immunocompetent pediatric patients who presented with URTI symptoms, had no known chronic disease, and were not receiving immunosuppression therapy formed the control group. Both groups were compared in terms of clinical manifestations, laboratory results, and PCR findings. Demographic data, clinical symptoms, laboratory findings, hospitalization status, length of hospital stay, and clinical outcomes were obtained from the electronic medical record system of Başkent University Hospital. Patients with available complete blood count, renal and hepatic function tests, and acute-phase reactants (C-reactive protein) were included. Exclusion criteria included episodes of acute rejection, stage 4 to stage 5 chronic kidney disease, active bacterial infections, or oncologic diseases. As systemic inflammation markers, the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII = neutrophil × platelet/lymphocyte) were calculated. All laboratory data were obtained from records corresponding to the first presentation of the illness.

Statistical analyses
We used SPSS software (version 26.0; IBM) for all statistical analyses. We used the Shapiro-Wilk test to assess data distribution. Continuous variables were expressed as mean ± SD for normally distributed data or as median values (with IQR) for nonnormally distributed data. Categorical variables were presented as frequencies (with percentages). We used the Student t test or the Mann-Whitney U test, as appropriate, to make comparisons between the KTR and control groups. We used the Pearson χ2 test or the Fisher exact test to compare categorical variables. P < .⁰⁵ was considered statistically significant.

Results
Of 111 pediatric patients with URTI included in the study (Table 1), 31 were KTR patients and 80 were immunocompetent patients (control group). The KTR group was significantly older than the control group (median 12.0 [7.3-15.7] years vs 7.5 [5.0-9.2] years, respectively; P < .⁰⁰¹). The sex distribution was similar between groups (male: 58.1% vs 51.2%, respectively; P = .³³³).

Hematology and biochemistry
In complete blood count parameters, leukocyte and neutrophil counts were higher in the KTR group versus the control group; however, the differences were not significant (white blood cells: 10.4 ×10³/µL [7.8-11.9] vs control 7.2 ×10³/µL [5.0-10.3]; P = .¹⁵⁴; neutrophils: 6.4 ×10³/µL [4.9-7.5] vs control 4.2 ×10³/µL [2.8-7.1]; P = .²³⁶). Lymphocyte levels were comparable between groups (2.26 ± 1.62 ×10³/µL vs control 2.27 ± 1.41 ×10³/µL; P = .⁹⁷⁹). The NLR was significantly higher in the KTR group versus the control group (4.3 [1.4-1.8] vs control 2.7 [1.5-1.9]; P = .⁰⁰¹), whereas platelet counts were lower (279.0 [207.0-358.0] vs control 289.5 [186.0-647.0]; P = .⁰⁰⁴). No significant differences were observed in the SII or PLR (P = .⁹⁶⁹ and P = .¹¹⁵, respectively). Renal function parameters (blood urea nitrogen, creatinine, and uric acid) were significantly higher in the KTR group compared with the control group, that is, blood urea nitrogen was 17.0 mg/dL (10.0-38.0) versus control 11.0 mg/dL (5.0-16.0) (P < .⁰⁰¹); creatinine was 0.78 mg/dL (0.45-1.35) versus control 0.50 mg/dL (0.38-1.08) (P < .⁰⁰¹), and uric acid was 4.9 mg/dL (4.5-10.7) versus control 3.5 mg/dL (2.3-7.9) (P = .⁰⁰²) (Table 1, Figure 1). Similarly, liver enzymes (aspartate aminotransferase and alanine aminotransferase) were higher in the KTR versus the control group (aspartate aminotransferase: 44.96 ± 31.01 U/L vs control 32.74 ± 10.54 U/L; P = .⁰¹⁰; alanine aminotransferase: 19.0 U/L [10.0-40.0] vs control 16.0 U/L [10.0-58.0]; P < .⁰⁰¹). Hemoglobin values were similar (12.9 g/dL [11.7-14.1] vs control 13.1 g/dL [9.5-18.1]; P = .⁴⁹¹). Mean platelet volume was higher in KTR but not significant (P = .⁰⁷¹).

Virology
Multiplex PCR analyses revealed similar influenza A positivity rates between groups (KTR 32.3% vs control 47.5%; P = .¹⁰⁷). Influenza B (KTR 0% vs control 10.0%; P = .⁰⁶⁸), respiratory syncytial virus (A/B) (KTR 0% vs control 8.8%; P = .⁰⁹⁴), adenovirus (KTR 6.5% vs control 12.5%; P = .³⁵⁷), rhinovirus/enterovirus (KTR 19.4% vs control 15.0%; P = .⁵⁷⁷), and Streptococcus pyogenes (KTR 9.7% vs control 15.0%; P = .⁴⁶²) positivity rates were also comparable (Table 1). In contrast, SARS-CoV-2 positivity was observed exclusively in the KTR group (35.5%; P < .⁰⁰¹). Cycle threshold values were inconsistently recorded and therefore excluded from analysis.

Clinical course
Hospitalization rates were 16.1% in the KTR group and 8.8% in the control group (P = .²⁶¹). The mean duration of hospitalization was 4.2 ± 1.1 days in the KTR group and 3.5 ± 1.4 days in the control group (P > .⁰⁵). None of the patients required intensive care or mechanical ventilation. All KTR patients achieved short-term stabilization of renal function, and no long-term sequelae were recorded. No significant interactions were observed with respect to age or sex. However, the limited sample size may have reduced the statistical power of these analyses. Because data regarding comorbidities and immunosuppression regimens were incomplete, multivariate analyses were not performed.

Discussion
This comparative analysis of pediatric patients with URTI demonstrated that KTR patients exhibited a distinct inflammatory profile compared with immunocompetent controls, characterized by elevated NLR and reduced platelet counts, and expected increases in renal and hepatic biochemical parameters. However, hospitalization rates and length of stay were similar between groups. Our findings align with previously published cohort work that reported higher rates of influenza infection and higher rates of hospitalization among transplant recipients versus the general population.² Multicenter studies that were conducted during the 2009 H1N1 pandemic also demonstrated that solid-organ transplant recipients had increased rates of severe disease and intensive care unit admissions, supporting this vulnerability.^5,6,9 On the other hand, reports from several centers have indicated that COVID-19 tends to follow a mild course in pediatric KTR patients, with rare intensive care or fatal outcomes,^7,8.10 and this observation is consistent with our data, which showed that SARS-CoV-2 positivity was observed exclusively among KTR and was associated with favorable short-term outcomes. Previously published studies have reported that vaccine-induced immunogenicity to influenza is weaker in pediatric transplant recipients versus healthy control patients.^1,3,4 The elevated NLR values observed in our cohort, when interpreted together with the previously published findings, suggested that the kinetics of viral clearance and inflammatory resolution may differ between immunocompromised and immunocompetent children. Our study is among only a few studies to directly compare the clinical, laboratory, and virology profiles of pediatric KTR and healthy children during URTI using multiplex viral PCR panels. The demonstration that easily accessible inflammatory markers such as NLR and SII may behave differently in this specific patient population provides an important contribution to clinical monitoring. Nevertheless, the single-center, retrospective design, limited sample size, and absence of detailed information regarding immunosuppression regimens were key limitations of our study. Confirmation of these results in larger, multicenter prospective cohorts could strengthen the basis for infection management and vaccination strategies in pediatric transplant recipients.

Conclusions
In pediatric kidney transplant recipients, the inflammatory response profile and renal and hepatic function parameters during upper respiratory tract infection may differ from those observed in immunocompetent controls. However, with appropriate follow-up and supportive care, short-term clinical outcomes are generally favorable. Early molecular diagnosis, close clinical monitoring, annual inactivated influenza vaccination, and timely initiation of antiviral therapy when indicated may help prevent complications in this vulnerable population.