Campbell was turned away from a blood donation drive in Rio de Janeiro because she had surgery to remove a cyst earlier this year.
Doctors said donors in Brazil must wait six months after having an operation before they become eligible to donate.
Campbell told reporters she would return to give blood at a later date.
Fatal
"Unfortunately I can't give blood for Rio de Janeiro, but I'll surely be back," said the 37-year-old after being turned away at the HemoRio medical centre in Rio.
She added that she had seen a report about the epidemic on a TV report in London and decided to fly over and offer assistance.
The Brazilian state of Rio de Janeiro has been affected by a dengue fever outbreak since the beginning of year.
It has claimed 83 lives, with at least 51 deaths in the city of Rio itself.
The mosquito-borne disease causes high temperature, headaches and muscle pain and, in extreme cases, can be fatal.
Campbell, who was recently banned from British Airways flights after a row over missing baggage, is a regular visitor to the country.
Earlier this month, she was arrested on suspicion of assaulting a police officer after the incident at Heathrow Airport and later released on bail.
Source: MJFM
