The three most potentially serious medical problems that I encounter most often, when processing clients' applications for health insurance are 1) Hypertension (high blood pressure), 2) Hyperlipidemia (high blood Cholesterol), and 3) Diabetes (high blood sugar).
These conditions are "potentially" serious, because this blood flows through the most vital organs of our body. If these problems with the blood are not brought under control, they will eventually cause serious damage to these vital organs and can lead to a very serious heart attack, or other serious medical problems.
The bad news about these conditions is that they can't be cured (for now) and they will always be excluded from coverage if the problems existed at the time of application for insurance. (Yes, yes, yes...I know that some of you probably find this hard to believe, because you come from countries where the government gets involved in assuring that everyone has health coverage and pre-existing conditions are covered.
The good news is that, while these conditions can't be cured, they very definitely can be controlled - if you have the commitment and you seek reliable medical support to do so. The damage caused to vital organs develops over a long period of time and can be prevented if controlled soon enough (check with your doctor about this).
But, from an insurance company's perspective, even if you do bring the problem under control, the danger of you losing control still persists.
You lost control of the problem once, so you can still lose control of the problem again. It might be ideal for you if they removed the exclusion and just allowed you to submit proof every year to the insurance company showing that the problem is fully under control. But, monitoring that proof would be too difficult and costly for them. So, the exclusion would have to remain, no matter how well the condition has been kept under control.
The big question is: If you are excluded from coverage for treatment, medication and testing for high blood pressure, high cholesterol or diabetes, and any problems related to them, would you be covered for treatment of a heart attack, for example? The answer to that would depend on the treating physician. These conditions, if allowed to get out of control, leave tell-tale signs that let the treating physician know if they could be responsible. If those signs don't exist, then treatment of the heart attack should be covered; unless, of course, there were other reasons for not covering it stated in the policy.
We were able to put this to a test a few years ago when one of our inbound travel insurance clients arrived in Bangkok, departed from the plane, and then collapsed from a heart attack. It turned out that the insured had a history of high blood pressure which he kept under control with medication.
The insurance company's first response was, "Ah, ha! Got you!" (Or, something to that effect). But, the treating physician replied back, "Ah, ha! No, you don't!" (Or, something to that effect). The treating physician stated very emphatically that the insured's history of high blood pressure had nothing to do with his heart attack. The insurance company then paid the claim in full. Well...except for the drinks in the refrigerator in his room which he tried to claim for.
Let this story be a lesson for you: The drinks you take from the hospital room refrigerator are not covered by your health insurance.