Objective: To determine if levels of interleukin (IL) 5, IL-6, and IL-10 or their ratios in nasal secretion are diagnostic of viral upper respiratory tract infections (vURTIs) and coldlike illnesses (CLIs) in children.

Design: Longitudinal study of children for vURTIs, CLIs, and concentrations and ratios of nasal cytokines.

Setting: Outpatient assessments of children.

Participants: A total of 224 children, aged 1 to 9 years.

Main outcome measures: Concentrations of IL-5, IL-6, and IL-10 in nasal secretions, vURTIs diagnosed by polymerase chain reaction (PCR) detection of upper respiratory tract viruses, and concurrent CLIs diagnosed by parents.

Results: Of 1269 secretion samples, 552 (43.5%) were collected during a vURTI (PCR findings positive for an assayed virus [PCR(+)]). A concurrent CLI was diagnosed for 34% of the PCR(+) samples and for 18% of the samples found to be negative by PCR analysis (PCR(-)). Cytokine concentrations and ratios were highly variable and skewed to the lower values. The significance of the cytokine concentrations and ratios as discriminators of groups defined by the presence or absence of virus and of subgroups defined by the presence or absence of a CLI was evaluated using receiver operating characteristic curves. All measures were significant discriminators of the PCR(+) vs PCR(-) groups, and most were significant discriminators of the paired CLI subgroups. The concentration of IL-6 and the IL-5/IL-6 ratio were the best discriminators across all groups and subgroups. However, the sensitivities and specificities of those discriminators at the best cutoff values were on the order of 0.7 for the most extreme pairwise comparison (PCR(+)CLI(+) vs PCR(-)CLI(-)) and lower for the other comparison groups.

Conclusion: The low sensitivities and specificities for cytokine-based assignment of specimens to the paired groups and subgroups limit their usefulness for diagnosis of infection or illness.