Objectives: Infections, especially pneumonia, are among the significant causes of morbidity and mortality in transplant recipients. Pneumonia leads to a complex clinical circumstance, related not only to the infection itself but also to underlying immunosuppression, concomitant diseases, and organ dysfunction. Here, we evaluated the effect of the immunonutritional/inflammatory biomarker known as the HALP score (calculated from hemoglobin, albumin, lymphocytes, and platelets) on prognosis in patients who developed pneumonia after kidney transplant.
Materials and Methods: We retrospectively reviewed files of kidney transplant recipients treated at our hospital’s chest diseases outpatient clinic between April 2020 and April 2025 to discover patients who had been diagnosed with pneumonia on thoracic computed tomography scans. We exported data (age, sex, laboratory tests at diagnosis, length of hospital stay, and mortality rates) to a database spreadsheet file (Excel, Microsoft) and compared HALP scores of patients who died versus survived. We analyzed disease severity according to the Pneumonia Severity Index and the CURB-65 (calculated from confusion, uremia, respiratory rate, blood pressure, and age ≥65 years) scores.
Results: Among 178 included patients (100 female, 78 male), 148 (83.1%) survived and 30 (16.9%) died. Patients who died had HALP scores lower than patients who survived. Patients with higher Pneumonia Severity Index scores had significantly lower HALP scores.
Conclusions: The HALP score is a biomarker based on easily calculable, low-cost, and accessible parameters and may be a potential tool to evaluate prognosis in the general patient population. Prospective and multicenter studies with larger sample groups are needed to better evaluate the role of the HALP score for prognosis determination related to infections in kidney transplant recipients.

Key words : Biomarker, Kidney transplantation, Prognostic factor

Introduction
Kidney transplant improves survival and quality of life in patients with end-stage kidney disease; however, lifelong immunosuppression therapy increases susceptibility to infections.^1,2 The risk of infection is influenced by the degree of immunosuppression, underlying comorbidities, graft function, and environmental factors. Pneumonia remains a common and serious infectious complication after kidney transplant and is associated with substantial morbidity and mortality.^3,4 The etiology of posttransplant pneumonia is diverse and includes bacterial, viral, and opportunistic pathogens. In addition, prolonged hospitalization, previous antibiotic exposure, and impaired immune defenses increase the risk of severe infection and adverse outcomes.^4,5 The CURB-65 (confusion, uremia, respiratory rate, blood pressure, and age ≥65 years) and Pneumonia Severity Index (PSI) scores are widely used tools for disease severity assessment and mortality prediction in patients with community-acquired pneumonia.^6,7 Recently, interest has increased in simple laboratory-based prognostic markers. The HALP score (calculated from hemoglobin, albumin, lymphocytes, and platelets) is an inexpensive and easily calculated index that reflects nutritional, inflammatory, and immune status. Previous studies have demonstrated its prognostic value in several inflammatory conditions, including sepsis, but the role of the HALP score in kidney transplant recipients with pneumonia remains unclear.⁶ Therefore, we aimed to evaluate the prognostic significance of HALP scores in kidney transplant recipients who developed pneumonia and to investigate the association of the HALP score with established clinical severity scores, including PSI and CURB-65.

Materials and Methods
This retrospective multicenter study was conducted using data collected for the period April 2020 through April 2025 from 2 tertiary care centers. For this period, we retrospectively reviewed all medical records of hospitalized kidney transplant patients. We included all patients who were diagnosed with pneumonia based on at least 1 clinical finding (cough, shortness of breath, sputum, positive physical examination findings, or other clinical symptoms such as fever) and with positive results for radiology imaging. We excluded any patients under 18 years of age, patients without a history of renal transplant, patients for whom the diagnosis of pneumonia could not be confirmed clinically and radiologically, patients with another active focus of infection, patients with incomplete laboratory data that did not allow for the calculation of the HALP score, patients with hematological malignancies, and patients with insufficient clinical follow-up data. Our study was conducted in accordance with the principles of the Declaration of Helsinki, and written informed consent was obtained from all participants. The study received approval from the university’s local ethics committee (protocol No. KA: 25/280). For patients who met the inclusion criteria, we used patient files and the hospital information management system to record demographic characteristics (age and sex), laboratory parameters (hemoglobin, albumin, lymphocyte, and platelet levels), length of hospital stay, need for intensive care, and mortality status. The HALP score was calculated for each patient from laboratory values obtained at the time of admission. From the complete blood count and biochemistry results of the patients included in the study, HALP scores were calculated based on hemoglobin (g/L), serum albumin (g/L), lymphocyte count (×109 cells/L), and platelet count (×109 cells/L). The HALP formula is the product of the first 3 factors (hemoglobin × albumin × lymphocytes) divided by the last factor (platelets). We categorized and evaluated patients according to 2 groups: patients who died and patients who survived. We compared HALP scores and other clinical parameters between these groups.

Statistical analyses
We presented continuous variables as median values (with minimum and maximum) and categorical variables as frequency (with percentage). We evaluated the distribution characteristics of continuous variables in terms of normality and used nonparametric methods in group comparisons due to the failure to meet the assumption of normal distribution. To examine the difference between the 2 groups according to 30-day mortality, we used the Mann-Whitney U test for continuous variables and the χ2 test for categorical variables. We examined the association between mortality and PSI, CURB-65, and HALP scores using the Spearman rank correlation coefficient (rho). To examine the associations between the PSI and CURB-65 scores and laboratory and clinical variables, we compared continuous variables using the Kruskal-Wallis test and compared categorical variables using the χ2 test. With variables for which a significant difference was found in the Kruskal-Wallis test, we used the Dunn post hoc test (with Bonferroni correction) to determine the difference between score levels (stages). In all tests, the 2-sided significance level was accepted as P < .⁰⁵.

Results
A total of 178 kidney transplant recipients (100 female, 78 male) with pneumonia were included in the study, of whom 148 (83.1%) survived and 30 (16.9%) died. There were significant positive correlations with mortality for the PSI score (r = 0.40, P < .⁰⁰¹) and the CURB-65 score (r = 0.33, P < .⁰⁰¹) , whereas the HALP score showed a significant negative correlation with mortality (r = -0.18, P = .⁰¹⁹). Compared with survivors, nonsurvivors were older and had significantly higher PSI scores, longer hospital stays, and higher values for platelet-to-lymphocyte ratio, whereas albumin, lymphocyte, platelet, and HALP values were significantly lower (Table 1, Figure 1). Mortality was also significantly associated with sex, intensive care unit (ICU) admission, and higher PSI and CURB-65 categories (Table 2, Figure 2). The HALP values decreased significantly with higher PSI severity (Table 3). Post hoc analysis showed a significant difference only between PSI stage 2 and PSI stage 5 (P = .⁰⁴¹). Although HALP values also tended to decrease with higher CURB-65 stage, this association was not significant (Table 4). Significant differences across PSI stages were observed for age, albumin, lymphocytes, HALP score, length of hospital stay, ICU admission, and mortality outcomes (Table 5, Figure 3, Figure 4). Higher PSI severity was associated with lower albumin, lymphocyte, and HALP values and higher rates of ICU admission and mortality. Similarly, age, PSI score, albumin level, length of hospital stay, ICU admission, and mortality outcomes differed significantly across CURB-65 stages (Table 6, Figure 5, Figure 6). Higher CURB-65 scores were associated with worsening clinical status, prolonged hospitalization, and higher mortality.

Discussion
Pneumonia remains a major cause of morbidity and mortality in kidney transplant recipients, largely due to chronic immunosuppression and impaired host defenses.^8,9 In our present study, we evaluated the prognostic significance of the HALP score in kidney transplant recipients who developed pneumonia and investigated the association of HALP scores with established severity scores. Consistent with previous studies, older age was associated with higher mortality.^10,11 Patients who died also had lower levels of hemoglobin, lymphocytes, albumin, and platelets. These findings are clinically relevant, because anemia may contribute to tissue hypoxia, lymphopenia reflects impaired cellular immunity, hypoalbuminemia indicates poor nutritional and inflammatory status, and thrombocytopenia has been linked to adverse outcomes in pneumonia.^12-14 The HALP score, which integrates hemoglobin, albumin, lymphocyte, and platelet levels, has emerged as a practical marker that reflects both nutritional and immune-inflammatory status.^15,16 Previous studies have demonstrated the prognostic value of the HALP score for malignancies, cardiovascular disease, and sepsis.^17-19 Although evidence regarding pneumonia is limited, low HALP scores have been associated with higher mortality in patients with severe COVID-19 pneumonia.²⁰ Similarly, in our study, HALP scores were significantly lower among nonsurvivors, suggesting that HALP may serve as a useful prognostic biomarker in kidney transplant recipients with pneumonia. The PSI and CURB-65 scores are widely used tools for pneumonia severity assessment and mortality prediction in the general population.²¹ However, the performance of the PSI and CURB-65 scores in immunocompromised and transplant populations remains controversial.^22,23 In our cohort, both PSI and CURB-65 scores were significantly associated with mortality. Furthermore, HALP values decreased as PSI severity increased, which indicated an association between worsening clinical status and impaired nutritional-inflammatory reserve. Overall, our findings suggest that the HALP score may complement established clinical scoring systems. The combined use of HALP, PSI, and CURB-65 scores may provide a more comprehensive assessment of prognosis in kidney transplant recipients who develop pneumonia.

Limitations
The main limitations of this study were its retrospective design and relatively small sample size, which may limit the generalizability of the findings and preclude causal inferences. In addition, immunosuppression regimens, etiological agents of pneumonia, and other potential confounding factors could not be analyzed in detail. Despite these limitations, our findings suggest that the HALP score may serve as a practical prognostic marker in kidney transplant recipients with pneumonia and warrant further validation in prospective multicenter studies.

Conclusions
The HALP score was significantly lower in kidney transplant recipients who died from pneumonia and may serve as a simple, accessible, and cost-effective prognostic biomarker in this population. In addition, higher PSI and CURB-65 scores were associated with increased disease severity and mortality, suggesting that the combined use of these scoring systems may improve prognostic assessment in posttransplant pneumonia.