Clsi Ep28 -

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.

The conflict tore the lab apart. Clinicians started calling. A healthy medical student with a TSH of 3.8—perfectly fine by the old book—was now flagged high. An exhausted intern with a TSH of 0.5 was flagged low, even though she felt fine after a night shift. clsi ep28

She called Mrs. Park’s family. The levothyroxine was stopped. The arrhythmia resolved. She pulled the raw data from her 120 healthy subjects

So when the new automated immunoassay analyzer arrived, she knew the drill. The manufacturer’s reference intervals for thyroid-stimulating hormone (TSH) were neatly printed in the manual: 0.4–4.0 mIU/L. But EP28 was clear: Verify before use. Don’t trust, verify. The elderly subgroup, small as it was, had

Mrs. Eleanor Park, 68, came in for fatigue. Her TSH was 3.9 mIU/L—within the manufacturer’s range but above Aliyah’s verified upper limit of 3.2. Using the lab’s new narrow interval, the computer flagged it as Abnormal-High . The junior resident started her on low-dose levothyroxine.

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.

The lower limit of her in-house reference interval was 0.6 mIU/L. The upper limit was 3.2.