To the Editor:
We thank Drs. Koestenberger and Ravekes for their comments1. An integral part of validation of a biomarker is the definition of normal (and abnormal) values for the measure. For the …
Address correspondence to Dr. Mathai, Johns Hopkins University – Medicine, Division of Pulmonary and Critical Care Medicine, 1830 E. Monument St., Room 516, Baltimore, MD 21205, USA. E-mail: smathai4{at}jhmi.edu