Conventional wisdom says that dengue patients with low platelet counts should get a transfusion to prevent bleeding, but a landmark local study has proven otherwise.

There is no need for such transfusions if patients do not have complications, the study's authors say.

This is even if their platelet count drops below 20,000 per microlitre of blood - the level at which transfusions usually occur.

The findings may change the way public hospitals handle dengue patients, and free up blood platelet stocks for those who really need them.

In fact, those who received blood transfusions on top of the standard care were more likely to experience side effects than those who received only supportive care. These included rashes, chest pains and serious allergic reactions.

The study of nearly 400 dengue patients involved six public healthcare institutions in Singapore and one Malaysian medical centre.

The Adult Dengue Platelet Study was published in the prestigious Lancet journal earlier this month.

"With this study, the evidence is very strong," said Associate Professor David Lye, a senior consultant at Tan Tock Seng Hospital's Institute of Infectious Diseases and Epidemiology.

"It's quite clear - unless you have serious bleeding, you don't need a transfusion."

Changing the way things are done will ease the pressure on Singapore's national blood bank, where demand for platelets can skyrocket during major dengue epidemics, Prof Lye said.

For the study, both groups of dengue patients received the standard supportive care. One group received platelet transfusions as well.

However, the transfusions did not prevent people from bleeding or help them to recover their platelet levels more quickly, and were associated with side effects.

Singapore General Hospital, which was involved in the study, said that there is no standard protocol on when a transfusion should be done if a patient does not show signs of active bleeding, adding that there is a wide range of practices.

But the National University Hospital (NUH), which was also involved, said that it has stopped performing transfusions to prevent bleeding in dengue patients.

"We have already changed our practice since the study began, and do not give prophylactic platelet transfusions," said Associate Professor Sophia Archuleta, a senior consultant at the NUH infectious diseases division. Blood transfusions are done only if the bleeding is serious, she added.

In healthy people, platelet counts range between 150,000 and 250,000. In dengue patients, up to 20 per cent will have platelet counts below 20,000. Platelets are necessary for blood clotting and preventing bleeding. But only 3 per cent to 5 per cent of patients will have bleeding severe enough to warrant a platelet transfusion.