Quick answer: A caloric report describes how the two ears responded to low-frequency thermal stimulation. Unilateral weakness, directional preponderance and fixation suppression are measurements—not diagnoses. They must be interpreted with symptoms, examination, hearing results and, when appropriate, vHIT or other vestibular tests.
Do not read one percentage in isolation: laboratory methods and reference limits vary. A result cannot by itself prove Ménière disease, vestibular neuritis, migraine, a brain disorder or the cause of a patient’s dizziness.
Start with the four raw responses
A typical bithermal caloric test produces four principal responses: warm and cool stimulation of the right ear, and warm and cool stimulation of the left ear. The laboratory measures nystagmus, commonly using slow-phase velocity, and checks whether each response is technically adequate.
Before interpreting calculated percentages, the reviewer should consider ear anatomy, stimulation method, alertness, medicines, eye tracking, spontaneous nystagmus and whether all four responses were completed. A weak or absent set of responses can have technical as well as physiological explanations.
Unilateral weakness
Unilateral weakness (also called canal paresis in some reports) compares the total caloric response from one ear with the other. A significant asymmetry suggests that one horizontal canal pathway produced a smaller response under the test conditions.
It does not, by itself, identify the disease, its age or whether the patient is currently symptomatic. A compensated old peripheral loss, active vestibular disorder, technical limitation or another clinical context may produce different implications. The report’s own laboratory reference range should be used rather than importing one universal cutoff.
Directional preponderance
Directional preponderance (DP) compares the strength of right-beating and left-beating nystagmus across the irrigations. It does not simply mean that the ear on the same side is weak. DP can be influenced by spontaneous nystagmus, recovery after a peripheral event, testing conditions and central compensation.
DP is therefore usually a supporting observation, not a reliable locator or stand-alone diagnosis. The clinician should inspect the actual traces and baseline eye movements, not only the final percentage.
Fixation suppression
Visual fixation normally reduces vestibular nystagmus. During a fixation-suppression step, the patient is allowed to see a target and the change in nystagmus is measured. Reduced suppression can be clinically relevant, including in some central disorders, but it is not specific.
Poor attention, visual impairment, medicines, fatigue, inadequate stimulus and recording artefact can affect the result. It should be interpreted with the oculomotor examination—such as gaze, pursuit and saccades—and the neurological findings.
Why caloric and vHIT results can disagree
Caloric testing and the video head impulse test (vHIT) are not interchangeable. Calorics use a very low-frequency thermal stimulus and mainly assess the horizontal canal pathways one ear at a time. vHIT uses brief, high-acceleration head impulses and can assess all semicircular canals depending on the protocol.
Recognised patterns include abnormal calorics with a relatively normal horizontal vHIT, and less commonly the reverse. This may reflect frequency-specific vestibular function, the underlying disorder, stage of recovery or technical factors. Discordance should prompt clinical interpretation, not automatic dismissal of one test.
| Finding | What it may show | What it cannot prove alone |
|---|---|---|
| Unilateral weakness | Lower caloric response from one side | The exact disease, timing or symptom cause |
| Directional preponderance | Stronger nystagmus in one direction | Which ear is diseased |
| Reduced fixation suppression | Less visual reduction of nystagmus | A central diagnosis without supporting findings |
| Caloric–vHIT disagreement | Different response across stimulus ranges | That one of the tests is necessarily wrong |
Bilateral low responses
Low responses from both ears may raise concern for bilateral vestibular hypofunction, but the test must first be technically valid. Ear-canal factors, insufficient thermal transfer, medicines, poor alertness and incomplete stimulation can lower responses. Rotational-chair testing, vHIT, dynamic visual acuity or other tests may be considered according to availability and the clinical question.
How a clinician combines the report
- Confirm the symptom type, duration and triggers.
- Review hearing symptoms and audiometry.
- Examine spontaneous, positional and gaze-evoked eye movements.
- Check the raw caloric traces and technical notes.
- Compare vHIT or other vestibular tests when clinically relevant.
- Interpret the pattern in relation to migraine, episodic ear symptoms, acute vestibular loss, neurological signs and recovery.
For the appointment experience and preparation—not report interpretation—use the companion warm and cool caloric procedure guide. The vHIT guide explains the high-frequency head-impulse assessment.
Frequently asked questions
What does unilateral weakness mean?
It is an asymmetry calculation suggesting that one labyrinth produced a smaller caloric response under the test conditions. It must be interpreted with the clinical picture.
Is directional preponderance the same as a weak ear?
No. Directional preponderance describes stronger nystagmus in one direction and does not reliably identify a damaged ear by itself.
What does poor fixation suppression mean?
Reduced suppression can be clinically relevant, but attention, vision, medicines, recording quality and the complete oculomotor examination must be considered.
Can caloric and vHIT results disagree?
Yes. Calorics and vHIT probe different stimulus frequencies and can diverge in recognised vestibular disorders.
Can a caloric report diagnose the cause of vertigo?
No. The report should be combined with symptoms, examination, hearing data and other vestibular or neurological tests.
References
- Clinical significance of directional preponderance in caloric testing
- Dissociation between caloric and video head impulse test results
- Caloric and vHIT dissociation in vestibular disorders
Medical Disclaimer: This article is for educational purposes only and does not constitute medical advice, diagnosis or prescribing guidance. Consult Dr. Prateek Porwal at Prime ENT Center, Hardoi for personalised treatment.