Diagnostic accuracy of lateral neck radiography in ruling out supraglottitis: a prospective observational study.

Objective: To assess the diagnostic accuracy of lateral neck radiographs (LNR) for acute supraglottitis in adults.

Design: A single centre prospective observational study.

Setting: Emergency department at Kurashiki Central Hospital, Japan.

Participants: Adult patients who underwent LNR to detect supraglottitis.

Main Outcome Measures: Presence of supraglottitis, based on nasopharyngeal laryngoscopy or a follow-up telephone call, 7-30 days after the visit.

Results: 140 patients had LNR during the study period. 35 patients were excluded from further analysis because of lack of consent. Of the 105 eligible patients, 21 patients (20%) were given the diagnosis of supraglottitis: 17 of 29 with a radiographic abnormality, and 4 of 76 patients without a radiographic abnormality. Three of the four cases where LNR was negative was grade 1, and all cases of grade 3 or higher had abnormal LNR. Sensitivity and specificity (95% CI) of LNR for supraglottitis were 81.0% (64.2 to 97.7) and 85.7% (78.2 to 93.2), respectively. The positive predictive value of LNR was 58.6% (40.7 to 76.5) and the negative predictive value was 94.7% (89.7 to 99.8). The positive likelihood ratio of LNR was 5.67 (3.27 to 9.82) and the negative likelihood ratio was 0.22 (0.10 to 0.51).

Conclusions: LNR showed only moderate sensitivity and specificity for supraglottitis and would miss some cases of supraglottitis if the pre-test probability is high. LNR was very sensitive for grade 3 or higher supraglottitis, but would miss milder cases.

Trial Registration: UMIN000011928.