Clsi Ep28 Apr 2026

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

Aliyah recruited 120 healthy volunteers from hospital staff: non-pregnant, no chronic meds, no thyroid history. She drew their blood in the gold-top tubes at 8:00 AM sharp, spun them down, and ran them in duplicate. The data came back clean—but wrong.

She called Mrs. Park’s family. The levothyroxine was stopped. The arrhythmia resolved. 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. Three weeks later, Mrs

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 root cause analysis landed on Aliyah’s desk. She stared at the EP28 document, the same dog-eared copy she’d used for twenty years. And then she read the section she’d always skimmed: She drew their blood in the gold-top tubes

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.

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.