Sniff Test: Purpose, Test Details & Results

Modern medicine has a surprising array of ways to measure our senses, and the sense of smell is no exception! The "sniff test" is an umbrella term covering several clinical tools that evaluate olfactory function (how well a person can smell), as well as certain respiratory maneuvers that assess diaphragm strength in neuromuscular conditions. Understanding the sniff test’s purpose, the various test types, and how to interpret the results helps clinicians diagnose a wide range of conditions—from loss of smell (anosmia) to early signs of neurological diseases, as well as respiratory muscle weakness. Let’s explore how sniff tests work, what to expect, and how the results can shape patient care.

Purpose of Sniff Test

The sniff test plays a pivotal role in both otolaryngology (ENT) and pulmonary medicine, serving as a rapid, non-invasive tool to assess two major physiological domains: olfactory (smell) function and, in some versions, diaphragm strength. These seemingly simple tests can reveal much about a person’s health—from sinus and nasal problems to neurological disorders and muscular diseases.

Table 1: Main Applications of the Sniff Test

Why Assess the Sense of Smell?

Impairment in olfactory function is more than just an inconvenience—it can signal underlying disease. Olfactory testing is crucial in diagnosing and monitoring:

• Chronic sinus disease: Blocked or inflamed nasal passages can reduce smell.
• Neurodegenerative diseases: Early loss of smell can be a warning sign for Parkinson’s or Alzheimer’s disease.
• Congenital anosmia: Some people are born without a sense of smell.
• Post-infectious or post-traumatic loss: Viral infections (like COVID-19) and head injuries can cause sudden smell loss 1 2 5 10.

The Respiratory Perspective

In patients with neuromuscular disorders, the sniff test is also used to evaluate diaphragm strength—a key indicator of respiratory health. Here, the test guides clinicians in:

• Detecting early respiratory muscle weakness
• Monitoring disease progression
• Guiding interventions (e.g., non-invasive ventilation) 4

Novel Screening Uses

Beyond these clinical uses, innovative approaches have included using trained sniffer dogs to rapidly identify infectious diseases like COVID-19 in both laboratory and real-world settings 9.

Sniff Test Details

Sniff tests come in several forms, each tailored to answer specific clinical questions. Whether measuring smell or diaphragm strength, these tests are designed for accuracy, patient comfort, and reliability.

Table 2: Overview of Sniff Test Methods

The Sniff Magnitude Test

This innovative test measures the involuntary reduction in sniffing that occurs when a person encounters a bad odor. Unlike traditional tests, it minimizes cognitive demands and is suitable for children, people with cognitive impairment, or those from diverse backgrounds. The test involves:

• Presenting malodorous and non-odorous air streams
• Measuring sniff strength (sniff magnitude) as a reflex
• Comparing responses to diagnose olfactory dysfunction 1

"Sniffin’ Sticks" Test

A widely adopted psychophysical test, "Sniffin’ Sticks" uses pen-like devices to deliver controlled odors. It includes three subtests:

• Threshold Test: Detects the minimum concentration of an odor a person can perceive.
• Discrimination Test: Distinguishes between different odors.
• Identification Test: Matches odors to their names or pictures.

The test is validated, reproducible, and useful in both clinical and research settings. Extended versions allow for more granular assessment and tracking changes over time 3 6 7 8.

Universal "U-Sniff" Test for Children

Children pose unique challenges for olfactory testing. The U-Sniff test was developed to be:

• Simple and engaging (uses 12 odors familiar to young children)
• Reliable starting from age 3, especially effective at age 4+
• Used internationally, with normative data for over 19 countries
• Highly sensitive and specific for distinguishing normal smell from anosmia or hyposmia 2 5 10

A typical session involves presenting scents and asking the child to choose the correct answer from multiple pictures.

Diaphragm Sniff Ultrasound

For respiratory assessment, the sniff maneuver is paired with ultrasound imaging:

• The patient is asked to perform a sharp sniff through the nose
• Ultrasound measures the movement and velocity of the diaphragm muscle
• Results correlate with sniff nasal pressure and forced vital capacity—key indicators of respiratory function in neuromuscular disease 4

Sniffer Dog Test

A novel, non-traditional sniff test, trained dogs can detect specific diseases (notably COVID-19) by smelling samples or people directly. This method:

• Offers rapid, non-invasive screening
• Shows high sensitivity and specificity
• Is being piloted in settings like airports and schools 9

Sniff Test Results & Follow-Up

Interpreting sniff test results requires understanding both the underlying condition and the specific test used. Results inform diagnosis, monitor disease progression, and guide treatment plans.

Table 3: Interpretation and Clinical Actions for Sniff Test Results

Understanding Olfactory Test Scores

• Sniff Magnitude Test: A normal result is a reflex reduction in sniff strength when exposed to a bad odor. No or minimal reduction suggests impaired olfaction. This test correlates well with established olfactory tests and is especially useful for populations where complex tasks are impractical 1.
• "Sniffin’ Sticks": Results are compared with age-matched norms. Low scores indicate reduced olfactory function (hyposmia or anosmia), which may prompt further neurological or ENT assessment. The test’s high reproducibility makes it useful for monitoring change over time 3 6 7 8.
• U-Sniff: A score below 8 out of 12 is considered hyposmia in children; below 4 is anosmia. The U-Sniff can detect even moderate reductions in smell, often before a child or parent notices a problem. Improvement after interventions (like adenoidectomy) can be tracked with repeat testing 2 5 10.

Respiratory Sniff Test Results

• Diaphragm Sniff Ultrasound: Abnormal results indicate diaphragm weakness and possible respiratory compromise. This is especially important in neuromuscular diseases, where early detection can inform timely interventions such as non-invasive ventilation or physical therapy 4.

What Happens Next?

Depending on the findings, follow-up may include:

• Further diagnostic testing (imaging, lab work)
• Referral to specialists (ENT, neurology, pulmonology)
• Therapeutic interventions (e.g., surgery for adenoids, respiratory support)
• Monitoring progression (repeat olfactory or respiratory testing)

In some cases, such as infectious disease screening with sniffer dogs, a positive result is typically confirmed by laboratory testing before further action is taken 9.

Conclusion

The sniff test, in its various forms, is a powerful tool for both clinicians and researchers. Whether evaluating the sense of smell or respiratory muscle strength, these tests combine simplicity with strong diagnostic value. Here’s what we’ve covered:

• Sniff tests are used to assess olfactory function (smell) and, in some cases, diaphragm strength.
• Several validated tests exist, including the Sniff Magnitude Test, Sniffin’ Sticks, U-Sniff for children, diaphragm sniff ultrasound, and even sniffer dog programs.
• Results are interpreted using age- and population-specific norms, with clear cutoffs to guide diagnosis and management.
• Sniff tests are valuable for diagnosing and monitoring a range of conditions, including anosmia, hyposmia, neurodegenerative diseases, respiratory muscle weakness, and even infectious diseases.
• Follow-up depends on the results, often leading to further evaluation, specialist referrals, or targeted interventions.

Ultimately, sniff tests offer a window into both neurological health and respiratory function—reminding us that sometimes, the simplest tests can yield the most critical insights.