Apologies if this has been posted before, but I'm just reading this article : "Guidance in Subclinical Hyperthyroidism and
Subclinical Hypothyroidism: Are We Making Progress?" by Wilmar M. Wiersinga in the European Thyroid Journal, 2015; and loved this quote:
"Application of reference ranges to determine whether
or not a given TSH value is abnormal is not as straightforward as it looks. ‘What is normal?’ is almost a philosophical question, and its answer (that what is not abnormal) is fraught with difficulties. My favourite quote on
this issue is from Benson  : ‘The normal range has a vague but comforting role in laboratory medicine. It looms on the horizon of our consciousness, perfectly
symmetrical like a Mount Fujiyama, somewhat misty in its meanings, yet gratefully revered and acknowledged. Far from being pure and simple, however, like a cherished illusion of childhood, on close examination it proves to
be maddeningly complex and is indeed one of the most stubborn and difficult problems limiting the usefulness of clinical laboratory data.’ "