Background: Laboratory investigations may be added to existing requests either automatically on the basis of algorithms (reflex testing) or by laboratory professionals (reflective testing). The clinical utility of reflex and reflective testing is not fully established. We studied efficiency (number of tests that needs to be added to make a diagnosis) and effectiveness (number of diagnoses) of reflex and reflective testing in selected biochemical scenarios.
Methods: Using fixed rules, we prospectively measured efficiency and effectiveness of reflex and reflective testing in the following scenarios (reflex initiators in parentheses): (1) hypovitaminosis D (hypocalcaemia plus elevated alkaline phosphatase activity); (2) hypomagnesaemia (hypokalaemia or hypocalcaemia); (3) hypothyroidism (high thyroid-stimulating hormone [TSH]); (4) hyperthyroidism (low TSH); (5) haemochromatosis (reflex or reflective addition of iron studies, followed by reflective addition of genetic studies). Separately, using a different data-set, we examined the impact of varying TSH thresholds on outcomes in the biochemical diagnosis of hyper- and hypothyroidism.
Results: In patients aged over 55 y, 25-hydroxy-vitamin D <50 nmol/L could be predicted with > or =90% certainty when albumin-adjusted calcium was < or =2.1 mmol/L plus alkaline phosphatase >150 U/L. Higher numbers of tests were needed to make a diagnosis in other scenarios. In general, more diagnoses were made by reflex testing. Outside the euthyroid TSH range, efficiency of diagnosis of hyper- and hypothyroidism became asymptotic, while effectiveness declined.
Conclusions: Near-maximal efficiency of reflex testing can be achieved, depending on the reflex and diagnostic thresholds applied. Reflective and reflex testing are complementary activities, the clinical utility of which depends on the initiators used.