CHICAGO (Reuters) — Older patients whose red blood cell counts are even slightly out of the normal range are at higher risk of death and heart problems after major surgery, US researchers said on Tuesday.“This is the first study to show that even mildly abnormal levels (of red blood cells) could be detrimental in elderly men undergoing major surgery,” said Dr. Wen-Chih Wu of the Providence Veterans Affairs Medical Center and Brown University in Rhode Island.

The finding lends new insight into the potential risks from a common problem among the elderly, but some experts caution that physicians should not rush to treat patients without proof that they benefit.

Doctors have thought for some time that very high or very low levels of red blood cells could pose a risk ahead of surgery, said Wu, whose work appears in the Journal of the American Medical Association.

He and colleagues set out to see at what point abnormal blood counts become a risk factor. Most patients facing surgery get routine blood screening called a hematocrit. A reading that is too low in red blood cells signals anemia, while one that is too high points to a condition called polycythemia.

Wu said doctors have been a little fuzzy about whether slightly abnormal readings pose any risk.

The researchers studied 310,311 military veterans, mostly men, aged 65 or older who underwent major non-cardiac surgery between 1997 and 2004. Their blood was screened before surgery.

Then doctors checked to see how they fared 30 days after surgery. They found a 1.6 percent increase in the risk of death for every percentage point of deviation from the normal range for red blood cells.

“We now know there is a risk, and we know when that risk starts to creep up,” Wu said in a telephone interview.

The question now, he said, is what to do about it.

“We still don’t have that information yet,” Wu said.

“I would recommend that if you find abnormal levels of red blood cell counts before surgery we should investigate the underlying source. Sometimes things may be correctable.”

Anemia could be caused by slow bleeding somewhere in the body, for example.

But some doctors cautioned against treating patients <\m> especially anaemia patients <\m> without more study.

U.S. regulators in March imposed a strong warning on a group of anaemia drugs widely used by cancer patients because they carried a higher risk of death and blood clots.

“Since no intervention is without risk, clinicians should avoid using these findings ... to justify interventions ... outside the research setting,” wrote Dr. Farhood Farjah and Dr. David Flum in an editorial in the same issue of JAMA.

“In other clinical arenas involving patients with anaemia ... clinicians may have prematurely embraced the aggressive use of erythropoietic agents to boost red blood cell production ... only to learn later that despite their best intentions they may have been causing more harm than benefit,” they wrote. The study was funded by the US Department of Veterans Affairs.