Association between prognostic nutritional index and asthma in US children and adolescents: a cross-sectional study

To evaluate the independent association between prognostic nutritional index (PNI) and asthma risk in children and adolescents and to identify potential threshold effects. This cross-sectional study analyzed data from 11,196 participants aged &lt;20 years from NHANES (2003–2020). The diagnosis of asthma was determined based on questionnaire data. PNI was calculated as 10 × albumin (g/dL) + 0.005 × lymphocyte count (10³ cells/μL) and analyzed as both a continuous and tertile variable. Weighted multivariate logistic regression models assessed associations between PNI and asthma. Restricted cubic spline and two-stage regression models examined nonlinear relationships and threshold effects. Subgroup analyses evaluated association stability across populations. Among 11,196 participants, 1274 (11.5%) reported physician-diagnosed asthma. PNI was inversely associated with asthma risk (OR = 0.963, 95% CI: 0.933–0.995; <i>p</i> = 0.0235). Participants in the highest PNI tertile (T3: 45.014–56.010) had a 34% lower asthma risk than those in the lowest tertile (OR = 0.659, 95% CI: 0.486–0.895; <i>p</i> = 0.0081). Nonlinear analysis revealed an inverse L-shaped relationship (<i>p</i> &lt; 0.001), with a threshold at PNI = 43.40: above this level, higher PNI was protective (OR = 0.93, 95% CI: 0.87–0.98; <i>p</i> = 0.01). Subgroup analyses found no significant interactions (all <i>p</i> &gt; 0.05). Higher PNI levels are associated with reduced asthma risk in children and adolescents, with a protective effect at PNI ≥43.40. However, further research is required to elucidate the underlying mechanisms of this association and explore the potential of PNI as a predictive biomarker for asthma in children and adolescents.