The number of blood samples analysed by police has declined 24 per cent in the region since 2013 - and a Tauranga barrister says it may be because more drink-drive defendants are satisfied with the reliability of breath testing results.
In the Bay of Plenty policing district, 423 blood samples were analysed in 2011. That number fell to 320 in 2013. Similar declines have occurred across the country, police statistics show.
Tauranga barrister Bill Nabney said an overall decline in police apprehension and blood testing could be responsible for the figures.
Another influence could be that more people are opting for an evidential breath test, which gives a more reliable blood alcohol reading than a breathalyser. The breath test can also used in court and is the option before blood testing.
"It's only if you refuse to do the evidential breath test that the blood test option comes alive," Mr Nabney said.
He said it was an interesting trend as blood tests have become more available to defendants in the past few years.
"Before 2011, you only had the right to opt for blood [testing] if your evidential breath was 400-600 micrograms [alcohol per litre of breath.] Now as a result of higher court decisions, anyone who returns a positive evidential result can opt for a blood test. But that still wouldn't account [for the decline.]"
National manager of road policing Carey Griffiths said those charged would be asked to pay for the cost of medical analysis. But he said the reduction in both blood and breath samples was attributable to wider influences including alcohol licensing restrictions, NZ Transport Agency campaigns and ongoing police testing.
"The point of this is to provide deterrents through large testing of many people, creating the perception [of widespread deterrence.]
Lowering the breath alcohol limit to 250mcg from December 1 had been another influence.
"We regularly strike people who think the drink drive limit's been lowered already."
Drivers who refuse an evidential breath test must undergo a blood test. Courts take the results of a blood test over results of an evidential breath test.
Independent nurses or medical staff usually take the samples as legislation means police cannot take blood tests.
Drivers also have the option of asking for their blood test to be conducted by an independent analyst.
Refusing to give blood sample
Land Transport statistics show 1600 drivers a year refuse to provide a blood sample.
Police estimate an average of 8764 breath tests of drivers are undertaken each day in New Zealand and 100 people are charged with drink-driving - meaning about 36,000 are charged each year.
Land Transport Amendment Bill changes will lower the breath alcohol limit for adult drivers to 250mcg per litre of breath from December 1. The blood limit will reduce from 80mg of alcohol per 100ml of blood, to 50mg.
Section 67 of the Land Transport Act 1998 says any person convicted of an offence against some sections of the act "is liable to pay the blood test fee" and "any associated medical expenses".