The Note Never Says What the Test Ruled Out
A short read on the sentence that goes missing between a normal test result and a discharge decision. A composite of cases I see repeatedly, with no detail drawn from any actual matter.
An emergency department record lands on your desk. A patient arrived with three days of ascending weakness (weakness starting in the feet and climbing) and severe back pain. A lumbar puncture (a spinal tap drawing fluid from the lower back) came back with normal protein, and the patient went home that evening diagnosed with a viral illness. The note records the result. It does not record what the result was taken to mean.
Was the test wrong? No. A normal protein this early is what Guillain-Barré syndrome (an immune attack on the peripheral nerves) produces. The European Academy of Neurology and Peripheral Nerve Society guideline is explicit: normal cerebrospinal fluid (the fluid around the brain and spinal cord) protein is common in the first week and does not exclude the diagnosis. The abnormality accumulates rather than arriving with the weakness: in the Dutch cohort that validated the Brighton criteria, protein was elevated in 49 percent of patients tapped on the first day and in 88 percent after two weeks. A tap on day three sits within a window where a normal result is ordinary.
Then was the discharge wrong? Not necessarily, and that is the harder point. A patient with a normal tap can be sent home defensibly. What makes it defensible is not the result but the reasoning that accompanied it and the plan that followed.
So what is missing from the note? The sentence in between. The record moves from a laboratory value to a disposition with nothing between them, so the reader cannot tell whether the clinician knew a normal early tap excludes nothing or believed it excluded the disease. Those are different clinicians, and the note reads identically either way.
The error runs in both directions. A plaintiff expert who treats the normal result as the error has misread it: the result was correct and obtaining it was reasonable. A defense expert offering it as vindication makes the same error inverted, resting on a test that could not have excluded the diagnosis at the hour it was drawn. Both are arguing about a number that could not settle the question on that date.
So the question underneath is narrower than most reviews start with. Not whether the test was normal, and not whether the discharge was reasonable. Whether anyone asked what a normal result, on that day of illness, could establish.
Three things follow for a reviewer. A normal result dated day one and a normal result dated day ten are different findings, so every test here is read against the day of illness rather than the day of the visit. A test that cannot exclude a diagnosis cannot be offered as having ruled it out, whatever the disposition line says. And where the inference between result and disposition is missing, that absence is the finding, and it cuts either way.
Underneath this sits the medicine: which tests are uninformative in which week, and what the guideline advises be measured once a patient is admitted.
— T.B.K
Tobias B. Kulik, MD, FAAN
CorteXion LLC · Scientia et Veritas
The Primer in this month's Writings
Guillain-Barré Syndrome, Part I: What Was Measured, and When — cortexion.co/writings/guillain-barre-primer-part-1
Primary source
van Doorn PA, Van den Bergh PYK, Hadden RDM, et al. European Academy of Neurology/Peripheral Nerve Society Guideline on diagnosis and treatment of Guillain-Barré syndrome. Eur J Neurol. 2023;30(12):3646-3674. doi:10.1111/ene.16073
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