The U.S. Federal Reserve on Friday revised several banks' capital levels under stress a day after results of its closely watched industry health check were published.

The revisions did not cause any additional banks to dip below the 5 percent minimum for top-tier capital in the Fed's annual stress tests on the country's biggest banks.

Analysts pay close attention to the stress tests both because they help show the industry's strength and because regulators use the results to determine whether banks can return capital to shareholders.

Most of the 30 banks in the test either had no change in their capital ratios under stress or at most a 0.1 percentage point difference between Thursday's release and the corrected figures, the Fed said.

The biggest change was for American Express (AXP), whose minimum capital ratio under stress declined by 0.5 percentage point to 12.1 percent.

The one bank that fell under the minimum on Thursday, Zions Bancorp (ZION), saw its capital ratio revised up slightly to 3.6 percent on Friday.

M&T Bank (MTB), which had the next lowest capital level on Thursday, was revised up by 0.3 percentage point to 6.2 percent under stress. Northern Trust (NTRS) also saw its capital level revised up by that amount to end at 11.7 percent.

HSBC's (HSBC) North America unit saw its minimum tier 1 common capital ratio revised down by 0.2 percentage point to 6.6 percent.

Spokesmen for American Express, Northern Trust and M&T Bank all declined to comment. Representatives of Zions and HSBC did not immediately respond to requests for comment.

The Fed said the ratios were adjusted due to inconsistencies in the way the tests handled capital actions in the fourth quarter of 2013 and assumptions about compensation-related issues.

(Reporting by Emily Stephenson; Editing by Andrea Ricci and Leslie Adler)