Washington —- The blood test that screens millions of men for prostate cancer leads to so much unnecessary anxiety, surgery and complications that doctors should stop testing elderly men, and it remains unclear whether the test is worthwhile for younger men, a federal task force concluded Monday.

The PSA test, which measures a protein in the blood produced by prostate tissue, has significantly increased the number of men who are being diagnosed with prostate cancer at very early stages. But the U.S. Preventive Services Task Force said it remains unclear whether that translates into fewer deaths.

Prostate cancer often grows so slowly that many men who have the disease die from something else without ever knowing they had it.

Because it is not clear what PSA level signals cancer, many men have stressful false alarms that lead to unnecessary surgical biopsies.

"People say, 'What's the harm in screening?' In fact, there are several ways in which screening can actually be harmful," said Howard Parnes of the National Cancer Institute.