Fitness to Dive: Why the Medical Form Is Not a Formality
PFO, asthma, diabetes and certain medications can all change whether diving is safe. Here is why the medical questionnaire before a course matters.
Most divers meet the medical questionnaire as an annoyance, a page of tick boxes between them and the pool session they actually signed up for. Few read it as what it is: a screening tool built from decades of accident data, designed to catch the handful of conditions that turn an ordinary dive into a genuine risk.
It asks about things that seem unrelated to swimming underwater, a hole in the heart, an inhaler, a blood sugar meter. They are not unrelated. Each one changes how the body responds to pressure, gas, and exertion in ways that only show up once someone is thirty feet down.
Why a hole in the heart matters underwater
A patent foramen ovale, or PFO, is a small flap-like opening between the heart's two upper chambers that is present in everyone before birth and normally seals shut afterward, though it stays open in a meaningful share of adults without causing any everyday symptoms. The reason it matters to diving is specific: it can allow venous blood, carrying small nitrogen bubbles that form naturally during ascent, to bypass the lungs' filtering function and cross directly into arterial circulation, potentially reaching the brain or spinal cord.
According to guidance summarised on the fitness to dive medical reference, routine PFO screening is not recommended for every diver, but testing is considered when a diver has had more than one episode of decompression sickness involving neurological, spinal, inner ear or skin symptoms, since a pattern like that raises suspicion that a PFO may be involved. It is a targeted, not universal, screening decision, made after an event rather than before a first dive.
Asthma: a condition of degrees, not a blanket ban
Asthma sits on a spectrum in diving medicine rather than being an automatic disqualifier. The same fitness to dive guidance notes that divers whose asthma is triggered by exercise, cold, or emotional stress are generally advised against diving, because those are exactly the conditions a dive can produce, cold water, physical exertion, and occasional stress. But asthmatics who are well controlled, have normal lung function tests, and pass an exercise-based assessment may be cleared to dive.
The underlying concern is air trapping, if an airway narrows during ascent while a diver is holding breath or breathing irregularly, expanding gas in the lungs has nowhere to safely go, which can cause serious lung injury. That is a mechanical risk layered on top of the general risks of exertion, which is why the diving medical form asks specifically about asthma triggers rather than just whether someone has ever been diagnosed.
Diabetes: manageable, but with real conditions attached
Diving with diabetes is possible and increasingly common, but it comes with structure. Divers with diabetes are generally expected to be adults with well established treatment and stable blood glucose control, capable of maintaining that control through the changing physical demands of a dive day, according to the same fitness to dive overview. Annual medical evaluation is typically required, and divers over 40 are advised to be screened regularly for silent cardiovascular disease, since diabetes raises cardiovascular risk in ways that may not otherwise be obvious.
The core concern is straightforward: a diver whose blood sugar drops or spikes underwater faces impaired judgment and consciousness at the worst possible time and place, with no ability to simply stop and treat it the way they could on land. That is why glucose monitoring before and between dives is standard practice for divers managing diabetes.
Why the medical form exists at all
The PADI Diver Medical Participant Questionnaire and equivalent forms from other agencies exist to route divers into one of two paths: cleared to dive on the questionnaire alone, or referred to a physician for a specific evaluation before certification. It is not designed to exclude people with medical histories, it is designed to make sure the small number of conditions that genuinely change diving risk get a doctor's judgment rather than a self assessment.
This article explains the medical reasoning as journalism, not as medical advice. Whether a specific individual is fit to dive is a decision for that person's physician and a certified diving instructor, working from a properly completed medical form, not something to be concluded from a magazine article.
Medications that complicate the picture further
Beyond specific diagnosed conditions, the medical questionnaire also asks about current medication, because several common drug categories interact with diving physiology in ways that are easy to overlook. Sedating antihistamines and some anti-anxiety medications can worsen the very disorientation that nitrogen narcosis already causes at depth, some blood pressure and heart medications affect how the body handles exertion and thermal stress underwater, and decongestants that help with ear equalisation on the surface can wear off mid-dive, leaving a diver unable to clear their ears properly on ascent. None of this means medicated divers cannot dive, it means the questionnaire is designed to route those specific combinations to a physician's judgment rather than leave the diver guessing.
Why the form asks about age and general fitness too
The same fitness to dive guidance also flags general cardiovascular fitness as a screening consideration independent of any single named condition, since diving combines cold exposure, physical exertion, and occasional emotional stress in a way that can reveal an undiagnosed heart or lung issue that would otherwise go unnoticed on land. This is part of why many training agencies recommend, and some destinations require, a more thorough medical evaluation for older first time divers rather than relying on the standard questionnaire alone.
As diving keeps opening up to a wider, older, and more medically varied population, the honest answer on that questionnaire matters more than the box ticking ritual it can feel like. It is the one part of certification that exists purely to keep the rest of it safe.
Published in The Outspoken Digest
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