That's easy: NONE.
(Although I've addressed this previously, the question has come up again many times and I thought it'd be worth repeating.)
In other words, no heart scan score--100, 500, 1000, 5000--should lead automatically to procedures in someone who underwent a heart scan but has no symptoms.
This question is a common point of confusion.
In other words, is there a specific cut-off that automatically triggers a need for catheterization?
In my view, there is no such score. We can't say, for instance, that everybody with a score above 1000 should have a catheterization. It is true that the higher your score, the greater the likelihood of a plaque blocking flow. A score of 1000 carries an approximately 25-30% likelihood of reduced blood flow sufficient to consider a stent or bypass. This can nearly always be settled with a stress test. Recall that, despite their pitfalls for uncovering hidden heart disease in the first place, stress tests are useful as gauges of coronary blood flow.
But even a score of 1000 carries a 70-75% likelihood that a procedure will not be necessary. This is too high to justify doing heart catheterizations willy-nilly.
Unfortunately, some of my colleagues will say that any heart scan score justifies a heart cath. I believe this is absolutely, unquestionably, and inexcusably wrong. More often than not, this attitude is borne out of ignorance, laziness, or a desire for profit.
Does every lump or bump justify surgery, radiation, and chemotherapy on the chance it could represent cancer? Of course not. There is indeed a time and place for these things, but judgment is involved.
In my view, no heart scan score should automatically prompt a major heart procedure like heart catheterization in a person without symptoms. If a stress test is normal, signifying normal coronary flow (and there are no other abnormal phenomena, such as abnormal left ventricular function), then there is no defensible rationale for heart procedures. Heart procedures like stents and bypass cannot prevent heart attacks in future; they can only restore flow when flow is poor, or stop the heart attack that is about to occur.
However, EVERY heart scan score above zero is a reason to engage in a program of prevention.