Horizontal Swab Insertion in Nasal Cavity for Viral Antigen Test

1. Introduction

During the early stages of the pandemic, the technique for performing nasopharyngeal tests was clearly established [1,2]. However, as a significant number of instructional YouTube videos were found to be incorrect [3], our team prepared an illustrative video demonstrating the correct insertion into the inferior meatus [4]. This technique involves an initial perpendicular insertion of the swab in relation to the face, followed by a slight reorientation of approximately 7-9º cephalad, without cervical hyperextension.

The present communication aims to: 1) review the authorized antigen tests [5] and their corresponding patient instructions [6,7,8,9,10,11,12,13]; and 2) provide free open-access images and schema of the nasal cavity. These images are intended to aid in the proper introduction of the swab into the inferior meatus, minimizing damage to surrounding structures, in order to reliably reach the nasopharynx, the area with the highest viral load [14]. This is particularly relevant given that multiple cases of cerebrospinal fluid leakage have been reported following damage to the cribriform plate at the roof of the nasal cavity.

2. Materials and Methods

2.1. Prosections and illustrative graphic proposal.

Written consent for research and educational purposes is obtained from donors during their registration with the Body Donation Service of the Faculty of Medicine and Health Sciences at the University of Barcelona. Following their entry into the program, all ex vivo samples are fully anonymized.

Permission was granted by the Director of the Body Donation Service at the University of Barcelona to capture illustrative images from anonymized ex vivo nasal specimens used for teaching within the Faculty.

Coronal, sagittal, and parasagittal views of the nasal cavity were obtained, both with and without the nasal septum. In these images, key anatomical landmarks were outlined: the anterior, superior, and inferior boundaries of the nasal cavity, as well as the profiles of the inferior, middle, and superior turbinates. This was done to later create a graphical schema for potential use in patient instructions for antigen tests.

2.2. Introduction of the antigen test swab.

For illustrative purposes during the pandemic, a video was recorded demonstrating the introduction of a swab into the nasal cavity of one of the authors (seated, without cervical extension). This video was distributed to media outlets [4].

From this recording, screenshots were extracted to analyze the swab's orientation. Using Amira software, a horizontal reference line, perpendicular to the ground, was superimposed on the images. The facial axis was defined by a line connecting the superior orbital margin to the chin.

Two angles were then measured: 1) the angle between the facial axis and the horizontal reference line (perpendicular to the ground), and 2) the angle between this horizontal reference line and the swab itself (Figure 1)

2.3. Review of the instructions per patients of COVID antigen test

The list of authorized antigen tests in Spain, as detailed on the website of the Spanish Agency of Medicines and Medical Devices (AEMPS), was reviewed [5]. Subsequently, the official patient instructions for each available test were examined [6,7,8,9,10,11,12,13]

3. Results

3.1. Nasal cavity anatomical dissections.

Anatomical dissection images illustrating lateral (Figure 2A) and coronal (Figure 3) views of the nasal cavity were obtained. Notably, only a horizontal insertion angle (Figure 2B, green arrow) permits advancement along the inferior meatus—the narrow passage situated beneath the inferior turbinate (Figure 3).

3.2. Swab Insertion Technique

The facial axis was measured at an angle of 11º relative to the vertical plane. The optimal final insertion angle for the swab, which led to successful passage, was measured at 7–9º relative to the horizontal plane (Figure 1).

A composite schematic, created by outlining key anatomical features from the dissection images and video screenshot, is presented in Figure 4.

3.3. Review of the instructions for available antigen tests

All publicly available instructions for performing antigen tests [5,6,7,8,9,10,11,12,13] proposed insertion of the swab at vertical angles.

4. Discussion

Early evidence from the pandemic indicated a higher viral load in nasal samples—specifically those taken from the middle turbinate and nasopharynx—compared to oral samples [14].

While antigen tests became widely available to the general public in 2020, their initial performance was highly variable. An early 2020 Cochrane systematic review reported an average sensitivity of only 56.2%, with a range of 34% to 91% depending on the brand [15]. More recent reviews (2022–2025) confirm that this wide range in sensitivity persists even when tests are used according to manufacturer instructions [16], becoming a public health threat if many false negatives become undiagnosed.

Nevertheless, patients have reported difficulties in sample collection [17] and severe side effects, including CSF rhinorrhea caused by violation of the bony skull base through the lamina cribrosa [18,19,20,21], as well as meningitis [22]; additional cases have been recently reviewed [23]. If the swab is inserted vertically, or horizontally in a patient with cervical spine extension, following the patient instructions included with antigen tests marketed between 2020 and 2025, the swab may be directed toward the roof of the nasal cavity, where the fragile lamina cribrosa could be damaged.

Samples obtained from the mid-turbinate show comparable sensitivity to nasopharyngeal samples in children [24], in whom fragile nasal walls could increase the risk of side effects. PCR or antigen testing performed using nasopharyngeal lavage with isotonic saline has also been described as an alternative method to avoid discomfort while maintaining high sensitivity rates [25].

5. Conclusions

We recommend inserting the swab primarily horizontally, with a slight upward angulation of about 8º, and with the patient seated without neck extension. In cases where this standard technique is not feasible, such as with uncooperative small children, alternative methods like nasal lavage with saline prior to antigen testing should be considered.

Freely available images are provided for use in the development of updated patient instructions for antigen testing.