A second sample of blood was unnecessarily taken from England cricketer Graeme Swann, his drink-driving trial has been told.
Dr John Mundy, a forensic alcohol consultant, told Nottingham magistrates the second sample need not have been used when the first was suitable.
The expert defence witness also said that samples could be contaminated if they were "moved up and down".
Mr Swann, who denies drink-driving, was stopped by police in April 2010.
The court was previously told that he had drunk three or four glasses of white wine earlier in the evening to celebrate his birthday.
When he returned to his house in West Bridgford, he found one of his and wife Sarah's two cats - called Max and Paddy - stuck under the floor after builders had been working on their home.
Unable to find a screwdriver to undo the floorboards, Swann decided to drive his Porsche Cayenne to the nearest 24-hour Asda to buy a set of screwdrivers, the court heard.
He was stopped by a Nottinghamshire Police patrol car in Nottingham, and later gave two samples of blood.
It was the second that was analysed and showed Mr Swann's blood had 83mg of alcohol in 100ml of blood, which is over the legal limit of 80mg.
The court heard that nurse Lisa Hodgkinson took a second sample of 5ml of blood from Mr Swann as she feared her first sample of 2ml was not enough.
Dr Mundy said technically the first 2ml sample could have been used as 1ml was "ample".
He said: "I think this sample should have been sent to the laboratory.
"As the day-to-day head of the Metropolitan Police laboratory, if this had been done in the daytime, which this wasn't, obviously, an officer would have phoned me up and said 'Will this be OK?' and I would have said 'Yes'."
But under cross-examination from prosecutor Tara Kelly, Dr Mundy said the more blood that was taken, the better it would be as it would allow latitude for re-testing.
He said: "If I was pushed, I would recommend 4ml to be split into two bottles, that's 2ml per bottle.
"But obviously I am not suggesting that's the minimum amount suitable for analysis. But the more you have, the easier it is for the sample to be split and it's easier for the analyst to have more blood there."
Dr Mundy also said that sometimes samples could be contaminated by the rubber bungs used in the vials, which may have happened if the sample was "agitated" by moving it up and down.
In December, Mr Swann's solicitor Phillip Lucas argued there was no case to answer because the second sample was "unlawfully taken", but the judge ruled the trial should continue.
The cricketer was a key member of the England team that won an Ashes series in Australia for the first time in 24 years.
His trial began in August but has been adjourned several times because of his sporting commitments.
The hearing continues.