Clsi Ep28 -

Then came the case that changed everything.

Dr. Aliyah Vargas had run the University Hospital’s clinical chemistry lab for twelve years, and in that time, she had learned to trust two things: cold logic and the CLSI guidelines. EP28, specifically—the standard for defining, establishing, and verifying reference intervals—was her bible. It told her what “normal” looked like for a patient population. clsi ep28

Mrs. Park wasn’t abnormal. Aliyah’s reference population was just too young. Then came the case that changed everything

Aliyah nodded. “But EP28 says if we have 120 subjects, nonparametric ranking is the gold standard. The 2.5th and 97.5th percentiles are 0.6 and 3.2. That’s our truth.” Park wasn’t abnormal

Three weeks later, Mrs. Park was in the ER with atrial fibrillation—a known risk of overtreatment in the elderly.

“Reference intervals may need to be partitioned by age, sex, or other factors… especially for analytes like TSH, where values increase with age.”

She pulled the raw data from her 120 healthy subjects. Most were young—residents, techs, nurses under 40. Only seven were over 65. The elderly subgroup, small as it was, had a higher median TSH.