Neither Clearly Allergic Nor Clearly Eosinophilic: A Biologic Choice With No Dominant Marker
A woman with frequent severe asthma exacerbations tests negative for allergic sensitization and only borderline positive on every type-2 marker checked. The disagreement is what to do when the biomarker-matching approach that usually picks the biologic simply doesn't produce a clear answer.
A.F., a 36-year-old long-haul truck driver, has had asthma since childhood and has spent the past two years cycling through emergency rooms in cities she can now list from memory, always somewhere along whatever route she was driving that week. Five exacerbations requiring oral steroids in the past year have made it hard for her to keep her route schedule reliable, a real problem for a job that pays by the load rather than the hour.
Her biomarker workup, done carefully rather than assumed, refuses to point cleanly in one direction. Skin testing to a standard aeroallergen panel is entirely negative, and her total IgE is unremarkable at 38 IU/mL — no allergic phenotype to reach for. Her blood eosinophil count sits at 180 cells/µL, technically above the lower threshold some anti-IL-5 trials have used but well below the level associated with the strongest treatment effect, and her FeNO of 18 ppb is within the range generally read as low-normal rather than a type-2-high signal. Every individual number is either negative or borderline; none of them, alone, makes a confident case for a specific phenotype-targeted biologic, even though her exacerbation burden is severe and unambiguous by any clinical measure.
Her chart already says this, in other people's handwriting: prior physicians have noted more than once that her presentation never fit the usual allergic mold — no eczema, no rhinitis even in high-pollen months, no family history anyone can recall — and then carried on managing her as though it did. She has confirmed inhaler technique twice this year at two different visits, and her pharmacy refill records show no gaps, which leaves genuine, biologically discordant severe asthma as the honest description of what she has, rather than an adherence problem dressed up as a biomarker mystery.
Biologic selection conference, when no single biomarker leads
I'd still try the eosinophil pathway before reaching for anything else. 180 cells/µL is modest, but several of the anti-IL-5 trials, MENSA included, enrolled down to that range with real if smaller benefit, and it's the one number in her panel that's at least directionally positive rather than flatly negative. Something is better than nothing to aim at.
I'd go a different direction given exactly how discordant her picture is. Tezepelumab's own approval, built on NAVIGATOR, is specifically for patients like her — the drug's label doesn't require any biomarker threshold at all, because NAVIGATOR showed a real exacerbation reduction across the full range of eosinophil and allergic status, not just in the high-biomarker subgroup. When every individual number is borderline or negative, reaching for the one biologic that was never gated on a threshold in the first place seems more honest than picking the least-negative number and treating it as decisive.
The MENSA point is fair as far as it goes — some benefit at lower eosinophil counts is real. But 180 sits well below the range where that trial's own strongest effect was seen, and treating a borderline positive as a confident target reads more like reaching for the least negative option than following a real signal.
NAVIGATOR's own subgroup data actually answers this directly rather than leaving it as a general impression. Patients with lower baseline eosinophil counts, closer to her own 180, still showed a real if more modest exacerbation reduction with tezepelumab compared to placebo — the effect size scaled with eosinophil count, but it didn't disappear at the lower end the way a purely eosinophil-gated drug's benefit would. That's a closer match to her specific numbers than extrapolating from MENSA's own lower-enrollment tail, since tezepelumab's trial was actually designed and powered to include patients exactly like her.
This isn't a claim that anti-IL-5 would fail her — it might well work. It's that tezepelumab's own evidence base was built for precisely this discordant, no-dominant-marker picture, while anti-IL-5's strongest evidence sits at eosinophil counts meaningfully higher than hers.
Agreed: tezepelumab initiated today, with exacerbation frequency and oral steroid courses tracked explicitly over the next six months as the outcome that matters most given her occupational schedule pressure.
Not agreed: what response threshold at six months should prompt trying an anti-IL-5 agent instead. The allergist would switch after any exacerbation during that window given how borderline her eosinophil signal remains; the pulmonologist wants a full six-month assessment of overall exacerbation rate rather than reacting to any single event, given tezepelumab's benefit accrues over a full treatment course rather than showing immediately. Left for reassessment at the six-month visit.