Oscar Pistorius will receive a historic world silver medal on Saturday but the moment will be tinged with bitterness after he was left out of the 4x400m relay team for the final.

The controversial 'Blade Runner', who runs with carbon fibre prosthetic running blades, was a member of the South African 4x400m team that reached Friday's final, setting a new national record of 2min 59.21sec in the process.

But Pistorius, the first amputee to compete in the worlds, was slowest in a team that also included Ofentse Mogawane, Willem de Beer and Shane Victor -- and was dropped from the line-up for the final as a result.

The 24-year-old, who finished last in his semi-final heat in the individual 400m earlier in week, could not hide his disappointment at missing out although South African athletics officials defended their decision to leave him out.

"Haven't been included in the final for the SA men's 4x400m. Pretty Guttered," Pistorius said on his Twitter account.

And there would be no celebrations for Pistorius after his team-mates took silver behind a powerful United States team.

"Well done to the SA 4x400 relay team, they got a silver. Was really hard watching knowing I deserved to be part of it. Off to my bed, nyt all," he tweeted after the race.

Pistorius said the decision to drop him had been the choice of team management but he also defended his record.

"Re all the messages, receiving a lot of questions I dont know the answers to. Have the 2nd fastest time in SA and ran a 45.3 this wk," he tweeted. Pistorius ran 45.39 in his first outing in the individual 400m.

South Africa team leader Motlatsi Keikabile told AFP on Saturday that a specific line-up had been picked out of a squad of six with the final in mind and other teams had also made changes.

"You have six athletes and in the minds of the selectors you know this is the four I'm going to put in the qualifiers and this is the four I think will take us to the medal," she said.

"It's sad and it's not a pleasant experience for anyone to be told 'you will not be in the final' but it does happen because it's the country first and then yourself," she said.

"It's not emotional or sentimental. It's about getting glory for the country."

L.J. van Zyl, who ran the anchor leg in the final, with Victor taking Pistorius' place, explained the decision to drop Pistorius.

"We decided before the heats that the slowest runner on the team in the prelims would not run the final," said Van Zyl, who won individual bronze in the 400m hurdles.

"The first leg would decide the other legs. Unfortunately, Oscar's leg was the slowest and we made a decision this morning."

Pistorius said after the individual 400m that competing at the worlds had been "a dream absolutely come true", and that he would use the experience gained to improve as he targets next year's London Olympics.

The issue of whether his blades give Pistorius, cleared three years ago to run against able-bodied athletes, an advantage was back in the spotlight following his qualification for the worlds.

But he again rejected suggestions that he has an advantage.

The South African had both legs amputated below the knee when he was 11 months old because of a congenital condition that meant he was born without fibulae -- lower leg bones.

Pistorius failed to qualify for the 400m at the 2008 Beijing Olympics having been given the green light to attempt to qualify after the Court of Arbitration for Sport overturned a ruling by the IAAF (International Association of Athletics Federations) that his blades gave him an unfair advantage.