Perpendicular Swab Insertion in Nasal Cavity for Viral Tests

Abstract

Although self-administered antigen tests are widely available, anatomical knowledge of nasal anatomy in the general population is limited. Cerebrospinal fluid leakage has been reported in multiple cases following damage to the roof of the nasal cavity due to accidental penetration of the cribriform plate of the ethmoid bone. Methods: Images of anatomical prosections used for teaching in the Dissection Room of the Faculty of Medicine of the University of Barcelona were obtained to illustrate the viable pathway to the nasopharynx through the inferior meatus, below the inferior turbinate. Screenshots from publicly available videos produced by the author demonstrating perpendicular swab insertion were analyzed, and multiethnic illustrative images were taken from staff volunteers. Publicly available instructions for patients included in the first eight nasal antigen tests for self-diagnosis authorized in Spain in 2021 were reviewed. Results: Most of the initially authorized antigen tests (all but one) still recommended in 2025 a vertical swab insertion. However, successful insertion into the inferior meatus towards the nasopharynx can be achieved with a perpendicular approach. A schematic illustration for free use is provided. Conclusion: Swab instructions should indicate an insertion perpendicular to the face to access the inferior meatus safely and reduce the risk of injury to the ethmoidal cells.

1. Introduction

During the early stages of the pandemic, the technique for performing nasopharyngeal tests was clearly illustrated in 2020, showing a perpendicular insertion of the swab in relation to the face [1,2,3]. However, a significant number of instructional YouTube videos were found to be incorrect [4]. 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, among other complications, including meningitis [5,6,7,8,9,10].

Our team also prepared an illustrative video in 2021 [11] to guide the swab through the inferior meatus towards the nasopharynx, the area with the highest viral load [12].

The present communication aims to (1) review the nasal tests initially approved for self-diagnosis in Spain in 2021 and published in mass media [13], authorized by the Spanish Agency for Medicines and Medical Devices [14], and their corresponding patient instructions as of 2025, and (2) provide free open access images and schematics of the nasal cavity and an illustrative video to promote a perpendicular swab insertion, minimizing damage to surrounding structures.

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 facilities, all ex vivo samples are fully anonymized.

Permission was granted by the Professor of Human Anatomy and Director of the Body Donation Service at the University of Barcelona for the non-profit reuse of ex vivo images of the nasal cavity for online pandemic-related anatomical teaching at the public Faculty of Medicine. The images were used in a clinical session for the staff responsible for performing antigen or COVID-19 PCR tests at the public Primary Care center Anton de Borja in the metropolitan area of Barcelona in 2021. Additional images of similar material were taken for illustrative purposes for this communication in 2025.

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. Subsequently, a graphical schematic for potential use in patient instructions for self-administered antigen tests was created by superimposing the outlined profiles of the nasal cavity onto a facial profile.

2.2. Introduction of the Antigen Test Swab and New Instructions for Patients

For illustrative purposes during the pandemic, a video was recorded demonstrating the introduction of a swab into the nasal cavity in a seated position, without cervical extension. This video was distributed to media outlets [11]. The facial profile was used to superimpose the inner nasal cavity profiles and prepare a new proposal for patient instructions.

Additional images and one supplementary video [Supplementary Material S1] of perpendicular swab insertion were taken from multiethnic volunteers of different ages from the staff of the Primary Care Center Anton de Borja. Written consent was obtained from all volunteers.

2.3. Review of the Instructions for Patients Undergoing the COVID Antigen Test

The list of the first eight nasal antigen tests initially approved for self-diagnosis without medical prescription in Spain was published in the media by consumer associations in July 2021 [13], referring to the website of the Spanish Agency for Medicines and Medical Devices (AEMPS) [14]. The initially authorized tests were reviewed, and the official patient instructions for each listed test were examined [15,16,17,18,19,20,21,22].

The ex vivo images were rotated to simulate a cervical extension, as shown in the instructions for patients. A horizontal swab insertion was simulated to demonstrate the potential damage to the roof of the nasal cavity. An additional graphic to be incorporated into the instructions, explicitly recommending to avoid this approach, was created by outlining the swab insertion and nasal borders as described above.

3. Results

3.1. Nasal Cavity Anatomical Dissections

Anatomical dissection images illustrating lateral (Figure 1A) and coronal (Figure 2) views of the nasal cavity were obtained. Notably, only a perpendicular insertion angle (Figure 1B, green arrow) permits advancement along the inferior meatus, the narrow passage situated beneath the inferior turbinate, towards the nasopharynx (Figure 1).

3.2. Perpendicular Swab Insertion Technique

The perpendicular approach, which is independent of ethnicity, allows for the successful insertion of the swab into the inferior meatus to reach the nasopharynx (Figure 3).

By rotating the ex vivo sample and graphics to simulate cervical extension, we illustrate how a horizontal swab insertion combined with this posture could also potentially damage the roof of the nasal cavity by allowing the swab to reach the fragile cribriform plate of the ethmoid bone (Figure 4A,B). A composite schematic (Figure 4C,D) was created by outlining key anatomical features from dissection images and a facial profile from one of the videos.

Therefore, patient instructions should not only suggest a perpendicular swab insertion (Figure 4C) but also explicitly recommend avoiding cervical extension when inserting the swab horizontally (Figure 4D).

3.3. Review of the Instructions for Available Antigen Tests

Most publicly available instructions in 2025 for performing antigen tests propose a vertical insertion of the swab to obtain samples from the anterior nasal cavity, but one proposed a perpendicular insertion [20]. Some brands propose a horizontal approach with the patient in a cervical extension position [15,17].

4. Discussion

4.1. Perpendicular Swab Introduction: Anatomical and Clinical Evidence

The perpendicular introduction of instruments into the nasal cavity, together with the explicit recommendation to avoid more vertical approaches in order to reduce potential damage to the fragile roof of the nasal cavity, is described in otorhinolaryngology materials [23,24]. The video and images published by our team in 2021, emphasizing the perpendicular introduction of the swab for antigen testing [11], are similar to those published earlier in 2020 in The New England Journal of Medicine by the Division of Infectious Diseases at Brigham and Women’s Hospital in Boston [1,2]. Several authors from otorhinolaryngology departments, including those from Stanford University School of Medicine [3], among others [25], have shown a similar perpendicular insertion.

Although the anatomical ex vivo material presented belongs to Caucasian individuals over 70 years of age, as does the video in [11], the perpendicular approach is consistent across individuals with diverse craniofacial anatomies and does not depend on population background, being similar in non-Caucasian populations (Figure 3) [26].

The CAP Anton de Borja, a public primary care center in the metropolitan area of Barcelona where the human images were obtained, serves a cosmopolitan population of approximately 30,000 citizens, with more than 15% belonging to immigrant groups from diverse geographic backgrounds, primarily South America, Africa, and Asia. The collection team reviewed the anatomical content presented here in a clinical session in 2021. After four years of routine swab collection, no procedure-related complications were documented among more than 6000 COVID-19 diagnosed patients at this center [27].

4.2. Antigen Test Sensitivity

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 [12].

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 [28]. More recent reviews (2022–2025) confirm that this wide range in sensitivity persists even when tests are used according to manufacturer instructions [29], becoming a public health threat if many false negatives remain undiagnosed.

Samples obtained from the mid-turbinate show comparable sensitivity to nasopharyngeal samples in children [30], in whom fragile nasal walls and a reduced size 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 [31].

4.3. Antigen Test Side Effects

Nevertheless, patients have reported difficulties in sample collection [32] and, in rare cases, severe adverse events, including cerebrospinal fluid rhinorrhea resulting from violation of the bony skull base at the level of the cribriform plate [5,6,7,8], as well as meningitis [9]; additional cases have been reviewed recently [10]. Vertical insertion of the swab may direct it toward the roof of the nasal cavity, where the cribriform plate is particularly vulnerable. Similarly, cervical extension during the procedure may cause a horizontally introduced swab to be oriented toward the roof of the nasal fossa. Accordingly, patient instructions for antigen testing should recommend a perpendicular swab insertion without cervical extension.

5. Conclusions

We recommend that the swab be inserted perpendicular to the face, with the patient seated and without neck extension. When this standard technique is not feasible, such as in uncooperative young children, alternative sampling methods, including saline nasal lavage, may be considered.

Freely available images are provided to support updated patient instructions for antigen or PCR testing.