Changes in medicine have eliminated the need for millions of blood transfusions, which is good news for patients getting procedures such as coronary bypasses and other procedures that once required a lot of blood.

But the trend is wreaking havoc in the blood-bank business, forcing a wave of mergers and job cutbacks unlike anything the industry, which became large scale after World War II, has seen.

Transfusions are down almost one-third in the past five years, to about 11 million units last year from about 15 million units, according to the American Red Cross, which has about 40 percent of the market.

With “minimally invasive” techniques such as laparoscopic surgery and other shifts in medicine, demand for blood continues to drop despite population growth and a soaring number of people older than 65, who have the most surgeries requiring blood.

Blood-bank revenue is falling and may reach $1.5 billion this year from a high of $5 billion in 2008.

As fewer units of blood are used, hospitals, seeing strong supply and weak demand, are asking for a lower price per unit.

As a result, the blood-bank business has lost some jobs, and the losses will reach as high as 12,000 within the next three to five years, roughly a quarter of the total in the industry, according to the Red Cross. Officials there expressed some concern that the decline could reduce the system’s ability to respond to crises or to invest in new products or research.

From time to time since 2008, the Red Cross operated at a deficit. But it balanced its budget partly by cutting 1,500 jobs. Shaun Gilmore, president of Biomedical Services at the American Red Cross, said the organization was also looking to give up some real estate as it shrinks its operations.

Blood services amount to $1.8 billion to $1.9 billion of the group’s budget, which this year is about $3 billion, executives said. Of the organization’s 26,500 employees, 17,000 work in the blood program. The Red Cross wants the blood program to cover its own costs, or perhaps achieve a small surplus for reinvestment.

One reason for declining demand is that recent studies have found many transfusions unnecessary, so patients are no longer getting expensive services that did them no good.

The Society of Thoracic Surgeons, for example, changed the guidelines for transfusions after coronary-artery bypass grafts beginning in April 2012. A normal hemoglobin count is 12 to 16 grams per deciliter of blood, depending on gender.

Some doctors automatically ordered a transfusion after surgery; others did so only if the patient’s hemoglobin level fell to 10. Under the new guidelines, transfusion is not recommended until the level falls to seven.

“There’s overwhelming evidence to suggest that blood transfusion is a dual-edged sword,” said Dr. Victor Ferraris, a heart surgeon at the University of Kentucky in Lexington, who was the chairman of a committee that wrote the new guidelines. “Some people need it and it saves their lives; other people are harmed by it.”

In another approach, new guidelines emphasize treating patients for anemia in the weeks before surgery to minimize the need for transfusions. Cancer therapies have also changed in a way that reduces transfusion needs. So has surgery: In a total hip replacement, loss of 750 milliliters of blood, about 1.5 pints, was considered standard; now it is just 200 milliliters.

Doctors may be adopting the new guidelines faster because of the recent computerization of medical records, which allows a physician to order transfusions from a computer screen.

The computer, though, knows the guidelines, and it will alert a doctor if the order falls outside the norm. The same system can collect data on which surgeons routinely exceed the guidelines.

Insurance plans also discourage transfusions. Some, including Medicaid, pay hospitals a flat fee for a procedure, whether it involves the transfusion of one unit, two, three or none.

And blood is expensive. Nonprofit organizations collect whole blood from unpaid donors, but hospitals may pay $225 to $240 a unit, according to executives in the business, which covers a variety of costs, including testing.

If the unit is billed to the patient, the price can be $1,000 or more. Part of the expense is for storage, management and inventory losses; about 1 million units a year are discarded, mostly because they are not used soon enough.

“Blood is not a pharmaceutical that can sit on the shelf for 12 months or 18 months,” said Miriam Markowitz, chief executive of the American Association of Blood Banks. Red cells have a life of 42 days; platelets last five days. Hospitals must stock a variety of blood types and try hard not to run out of any category.

The reduction comes at a fortunate time, since the list of reasons for excluding blood donors seems only to get longer, reducing the pool of possible donors.

Because of the reduced demand for blood, potential donors may see emergency appeals less frequently, but the blood banks still issue them, during snowstorms, for example, and when donors are less likely to give, like during summer vacations and the December holidays. Even at reduced levels of demand, the blood banks need tens of thousands of donors a day.

In the meantime, the industry is going through a wave of mergers and acquisitions. America’s Blood Centers, an association of independent blood banks that includes the Puget Sound Blood Center, said its membership had fallen to 68 from 87 five years ago.

In July, the Institute for Transfusion Medicine, in Pittsburgh, said it would merge with OneBlood of Orlando, Fla. The new organization expects to distribute almost 2 million units of blood a year, making it one of the largest blood banks in the country.