The ‘70% claim’: what is the evidence base?

Those involved in the practice of laboratory medicine are convinced of its value to effective and safe patient care, and usually have much anecdotal evidence of instances in which appropriate testing or the provision of interpretative comments 1 have improved care. However, systematic evidence of the contribution of laboratory medicine to the overall process of diagnosis and management of patients is much harder to obtain – understandably so, in view of the multitude of factors that are involved in reaching a diagnosis and planning treatment for an individual. Many articles seeking to promote the value of laboratory medicine make use of what has become known as the ‘70% claim’. This presents itself in various forms, most commonly that ‘Laboratory medicine data influences 70% of clinical decisions’, 2 or minor variations around this figure (60 – 80%). The percentage of the electronic medical record that consists of laboratory medicine data is also often adduced in support of the importance of the contribution made by pathologists and clinical scientists to patient care. The earliest published reference to the claim, and the one most frequently cited, is from 1996, by Forsman at the Mayo Clinic in the USA. 3 The author states: ‘We know that, although the laboratory represents a small percentage of medical center costs, it leverages 60 – 70% of all critical decisions, e.g. admission, discharge and therapy’. The evidence for this is not provided in the paper, but in an interview with Clinical Laboratory News in 2004, Forsman is quoted as saying: ‘ ... the statements that have been made take two forms. The first is that the laboratory represents 5% of a health system’s costs, yet it affects 95% of the remaining costs. The second statement is that the laboratory contributes 80% of the objective data in the clinical record and influences 60% – 70% of critical decision making. Unpublished sources for these statements include conversations with Dr Peter Dysert at Baylor University in Houston,