The number of patients waiting more than six weeks for diagnostic tests has almost tripled in the past year.
However, waits remain historically low, according to NHS Information Centre data.
In March, 10,800 people waited more than six weeks for tests, up from 3,800 in the same month last year.
The number of patients waiting more than six weeks for both magnetic resonance imaging and echocardiography tests has more than quadrupled in the last year.
But the median waiting time for tests is still only 1.8 weeks compared with 4.9 weeks five years ago.
This year’s figure for those waiting more than 13 weeks was 849, compared with more than 200,000 in March 2006.
The maximum six week wait for diagnostics was introduced in 2004, but the coalition government stopped monitoring the targets centrally last July.
King’s Fund chief economist John Appleby said the figures showed a “slight trend upward” recently, but it was too early to tell whether this was down to the removal of targets.
He said the performance of diagnostic services had remained low with “ups and downs” since a “jagging fall” in 2006 and 2007.