How often can bleeding gums mean leukemia?

While this can. Be seen commonly in acute leukemia, and seeing large numbers of leukemia patients in my practice, i would find it common, my guess is that patients presenting to primary care docs or a dentist with bleeding gums rarely turn out to have leukemia.
Rarely. A periodontist can go an entire career and never see a case. The rule is for the dentist to be suspicious. If it does not respond to conventional treatment, look further and consider a referral.

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