The 35-year-old challenges Oleksandr Usyk for all four world cruiserweight titles in Manchester on 10 November.

Since starting his training camp in early September, Bellew has tested for the Voluntary Anti-Doping Association (Vada) and UK Anti-Doping (Ukad).

"I know they ain't testing others as frequently as me," Bellew tweeted.

Shortly after he was woken up for a test at around 06:00 BST on Wednesday, Bellew tweeted he was "struggling" with the disruption caused.

The former WBC cruiserweight champion provides doping authorities with details of his whereabouts at certain times but believes they arrive earlier than outlined.

"I'm all for a clean sport but they are messing up my sleep patterns every week now," he added.

"I'm trying my best to raise awareness but it's becoming a bit of a joke with the frequency of it. I have no problem doing a few tests a week but this 6am nonsense has to be better thought out."

In July, American tennis player Serena Williams said she had been tested five times in 2018 and questioned if others in her sport had provided as many samples.

Uniformity would help - Vada

Liverpool's Bellew says he has been tested three times by Vada and twice by Ukad since early September. Four of the tests have involved providing blood and urine, with one other requiring only a urine sample.

Bellew - who is outspoken in his criticism of drug cheats and has called for tougher sanctions - is also signed for testing by the World Anti-Doping Agency (Wada).

But Ukad, Wada and Vada all test independently and treat substances in different ways depending on if an athlete is deemed to be in a competition period or not.

Vada operates within boxing and Mixed Martial Arts and says both athletes in a bout will be tested the same number of times.

There is, however, no guarantee that national anti-doping organisations - such as Ukad in Bellew's case - will be as active or equal in administering tests in other countries.

Vada president Margaret Goodman told BBC Sport: "It would be helpful to not have athletes tested by national anti-doping organisations when Vada is involved as we are happy to share all our results with them."

Vada upholds only one prohibited list as opposed to differentiating between in- and out-of-competition periods when analysing substances. The body says its system is the "most stringent" for fighters.

Goodman continued: "I agree that uniformity would be helpful, and we are happy to work towards that goal with any national anti-doping organisation. With that said, it can't result in lessening Vada's standards or our testing profile."

Ukad told BBC Sport it employs an "intelligence-led risk-based approach to its testing programme".