The presently-disclosed subject matter provides methods and kits for diagnosing obstructive sleep apnea (OSA) in a subject, such as a human child, wherein a biological sample is provided from the subject and the amount of a Urocortin III peptide is determined from the sample. Further provided are methods for diagnosing OSA in a subject wherein the amount of a Urocortin III peptide and one or more peptides selected from a Uromodulin peptide, an Orosomucoid 1 peptide, and a Kallikrein 1 peptide are determined in a biological sample from a subject.