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Challenging breath test results

Blood tests

If a driver wishes to challenge the accuracy of the reading for an alcotest or breath analysis machine, he or she will have to undergo a blood test. If a blood test is not taken, the result of the breath test cannot be challenged other than in exceptional circumstances see consuming alcohol after driving.

  • All drivers recording over 0.05 BAC on a breath analysis reading have the right to undergo a blood test.
  • If a reading of > 0.05 is recorded, police are obliged to supply a form requesting a blood kit.
  • Tests must be conducted by a registered medical practitioner.
  • The kit contains a statement of the driver’s right to have a blood test together with instructions to both the driver and a medical practitioner on the procedures that must be followed.
  • The responsibility for making arrangements to have the blood sample taken lies with the driver. However, if outside metropolitan area and it appears to the police that the person will be unable to travel to a place to have a blood sample taken, the police must provide transport to a suitable place for the blood sample to be taken if requested.
  • If outside the metropolitan area, the blood test may be taken by a registered nurse.
  • The sample is divided into halves with one going to the driver and the other to the police. The police sample will be analysed with the results sent to the driver.
  • A driver may have their sample tested independently if they wish. If this is intended then it is important that the sample be kept in a cool place and analysed as soon as reasonably practicable.
Problems with challenging breath analysis results

A blood test will usually provide a reading lower than that provided by the breath analysis. This is to be expected because it is highly unlikely that the breath analysis and the blood test will be performed within the same hour. Usually a matter of hours will pass before the driver is able to get to a hospital and have a blood sample taken. During this time their blood alcohol level will naturally start to fall, provided they have not been drinking in the interim.

Alcohol elimination rate

When challenging the results of a breath analysis it is necessary to determine the alcohol elimination rate of the person concerned. The alcohol elimination rate measures the rate at which an individual eliminates alcohol from their blood. Alcohol elimination rates vary from person to person but generally between 0.01 to 0.02 gm of alcohol per 100 ml of blood per hour is considered within the normal range, in addition to a 25% margin of error.

Expert medical evidence required

In order to establish that a breath analysis reading was inaccurate, the results of the blood test must be explained and interpreted to the court by a medical expert who can provide evidence about the driver’s alcohol elimination rate at the time of the offence [Tonkin v Police [2006] SASC 145]. This would require further testing through a laboratory at the driver’s expense.

Challenging breath test results  :  Last Revised: Wed May 9th 2007
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