The Taoiseach has claimed that only 3% of over-70s will be stripped of their medical cards when strict new eligibility measures come into force.
As Health Minister James Reilly admitted he had concerns about achieving 113 million euro savings through his planned review of all medical cards issued, Enda Kenny insisted most elderly people have nothing to worry about.
The Taoiseach also insisted there would be no U-turns on budget decisions.
"The assessment process is the same for everybody," Mr Kenny said.
"So those people who are clearly under the income guidelines for medical cards need have no worries. Their cards are protected.
"The change made in eligibility affects a very small number of high earning people over 70 and when that change is completed, the proportion of people over 70 who either have medical cards or GP cards will still be in the high 90s, around 97%."
Around 35,000 over-70s are expected to lose their free health care on the back of new budget measures, which will see a reduction in the eligibility income threshold for a single person to 500 euro a week and to 900 euro for a couple.
The Government intends to save a total 113 million euro following an overall review of the provision of medical cards, which will see increased scrutiny and probity to ensure people who do not meet strict criteria do not avail of a card.
The Health Minister has been unable to explain how many people in total stand to lose their card as a result of the controversial decision.
But he insisted that existing policies will remain unchanged and that those who are genuinely eligible will not lose out.
"People who are entitled to their medical card have nothing to fear," he insisted.
Dr Reilly said official research had shown there was currently no equity in the criteria applied to people across the country - saying someone in one area could get a medical card while a person with the same criteria in another could not.
He said people would simply have to reply to a letter sent by the HSE outlining their eligibility.
"The HSE have been asked to draw up a plan and present it to me next Monday and the Taoiseach as well in relation to communication around this area," Dr Reilly said.
"People should not be afraid."
The minister, who appeared before the Oireachtas Health Committee, insisted a medical card is based on a person's finances - not their illness.
"The medical card scheme never operated on the basis of a medical condition or an illness. It operates on the basis of undue financial hardship," he said.
According to the HSE, almost two million people are covered either by a medical card or a GP visit card - 43% of the population.
It says that on October 1, 52,733 medical cards and 22,115 GP visit cards were issued where a patient was above the income threshold.
HSE director general Tony O'Brien told the health committee: "I and my colleagues are as committed to ensuring that all those legally entitled to medical or GP visit cards are able to avail of them as we are to fulfilling our absolute obligations to ensure that those who are not entitled neither receive or retain them."
He added that the assessment guidelines used for discretionary medical cards have not been changed since 2009.
Discretionary cards are granted to individuals who are not eligible for a full card due to their income, but whose illness causes "undue hardship" that requires state-funded help.
In cases involving terminal patients, the decision to grant a discretionary card can be made within 24 hours.
Dr Reilly said research revealed that almost half of those in possession of a discretionary medical card were almost 200% over the income threshold to qualify.
Meanwhile, the minister admitted he is worried about achieving the savings outlined in the health budget, which total 666 million euro.
"I am, frankly speaking, concerned around what can be achieved here and I'm concerned about what can be achieved around Haddington Road," he said.
"And that's why I asked for the Taoiseach's department and the Department of Public Expenditure and Reform to be involved in assessing and validating these figures, and also the impact they will have on the service."
Dr Reilly insisted all the figures outlined by his department in the Budget on Tuesday were "real".
"I can tell you there is no black hole now," he said.
"We know where all the money is, where it is spent, and where it is going and how much we need."