The relevant facts were as follows:
The Respondent (Plaintiff) had a mechanical heart valve inserted and, following the operation, she was required to take an anticoagulant medication for the rest of her life.
The Respondent was prescribed warfarin and as a consequence, she had to have her blood monitored regularly.
The Appellant is a firm of specialist medical pathologists which offered a warfarin care service where the Respondent attended for monitoring of her levels. In the period 13 to 25 February 2002, the Respondent had five blood tests which all showed her INR level as low, placing her at risk of developing thromboembolisms.
On 27 February 2002, the Appellant advised both the Respondent and her GP that they would no longer monitor her blood levels. The reason for this was that the Appellant formed the view that the Respondent was not complying with the required treatment.
The Court of Appeal concluded that in accordance with recognised common law principles, when loss or damage is proved to have been caused on the balance of probabilities by a defendant’s acts or omission, the plaintiff recovers the entire loss suffered, even if there was a forty-nine percent chance of it not occurring. Kiefel in Tabet v Gett referred to this as the ‘all or nothing’ rule. The Appellant’s contention that the Trial Judge’s findings on liability offended the principle in Tabet v Gett were therefore said to be baseless.