Serena Williams has called for equality when it comes to anti-doping procedures after figures showed she has been tested more than fellow American players in 2018.

A United States Anti-Doping Agency (USADA) database, available to view online, shows the 23-time grand slam singles champion has been subjected to five tests so far this year. In comparison, the likes of Williams' sister Venus, Sloane Stephens and Coco Vandeweghe have each been tested twice, while Madison Keys has had one test.

In a news conference at Wimbledon on Sunday, Serena said she had no problem with being regularly tested by authorities, providing everyone was subject to the same procedures.

Despise dishonesty

Discussing a recent conversation she had with USADA, Williams said: "Normally it goes on ranking. I get it even if I was number one. How is it I'm getting tested five times [now my ranking has dropped]? It's only June, I've been tested five times.

"I'm okay with that. Literally verbatim I said, ''I'm okay with that as long as everyone is being treated equally'. And that's all I care about.

"I despise having people in our sport who aren't being honest, so I'm totally okay with testing and I encourage it, but what I want to know is that everyone is getting tested and we are really working to keep this sport clean.

"Equality, that's all I've been preaching. If that's testing everyone five times, let's do it. Let's be a part of it.

"It's just about being equal and not singling one person out. Just due to the numbers, it looks like I'm being pushed out. Just test everyone equally."

Williams, who had to withdraw from the French Open through injury prior to a scheduled fourth-round match with Maria Sharapova, will face Arantxa Rus in her opening match at Wimbledon on Monday.