Thirteen of the 15-man squad plus five reserves were tested after flying back from South Africa, officials said on Friday.
Akhtar and Asif, who had doping bans controversially rescinded in December, will probably be tested on Saturday when they return from England.
Experts have warned that the pace duo, who face life bans if they test positive again, could still have illegal substances in their systems after being banned in November.
Pakistan are carrying out the tests apparently in response to criticism over the lifting of Akhtar and Asif's bans, which the World Anti-Doping Agency is challenging in the Court of Arbitration for Sport.
Captain Inzamam-ul-Haq said his team, beaten in both the Test and one-day series in South Africa, would struggle in the Caribbean if they lose the two bowlers.
"We need both Akhtar and Asif," Inzamam told reporters on team's arrival from South Africa.
"We definitely do not have replacements for Asif and Akhtar but I hope they would be there to play in the World Cup. It would be tough without them."
Akhtar and Asif have been included in the squad subject to clearing dope and fitness tests before the deadline of March 2, 11 days before the event starts.
Both tested positive for banned steroid nandrolone in October last year. A month later Akhtar was banned for two years and Asif for one year before their punishments were lifted on appeal.
Akhtar's contribution on the African tour lasted just one day when he took 4-36 in the Port Elizabeth Test, which Pakistan won.
The mercurial fast bowler returned home with a hamstring injury and has since hurt his left knee, an injury which makes him doubtful for the World Cup.
Asif featured in all three Tests and took 19 wickets but has since suffered a recurrence of an elbow injury and struggled in the one-day series.
Inzamam said he hoped every player passes the dope tests, whose results are due on March 1.
"If we play at our full strength then we have a good chance and I hope every players clears the dope tests," said Inzamam, adding he hoped to improve on his performance in South Africa where he scored just 74 runs.
"I will lift my performance in the key event like the World Cup," he said.
The Pakistan squad will start a short training camp on February 20 ahead of next month's World Cup, where they are in Group D alongside the West Indies, Zimbabwe and Ireland.
Pakistan will open the tournament against hosts West Indies on March 13.