What changed in ten years and what is newly possible or cheap — potassium monitoring in CKD

1. Summary

The domain's dossier already establishes that no cleared device measures potassium non-invasively and that ECG-based hyperkalemia inference has no product-code family of its own. What this report adds is the shape of what is being built underneath that gap. Ion-selective sensing has gotten smaller and cheaper at the bench — a wafer-scale graphene field-effect transistor array now claims plasma-potassium accuracy from under 30 microliters of sample [1] — and multiplexed, microneedle-based interstitial-fluid electrode arrays can track potassium continuously in non-human models [2][3], though none of this has reached a human clinical study. Separately, a second wave of ECG-based, non-blood hyperkalemia-screening entrants beyond AliveCor has started registering trials: AccurKardia's AK+ Guard is recruiting CKD outpatients on an already-cleared ambulatory ECG platform [4][5], and an independent 32-patient dialysis cohort has completed a correlation study of a wearable single-lead ECG against serum potassium [6]. On the regulated analyzer side, FDA's potassium ion-selective-electrode product code shows a small increase in clearances over the last five years against the prior five, while the creatinine enzymatic- electrode code is flat [7][8] — modest, and read as a floor rather than a trend given how few clearances either code carries in absolute terms.

2. What Changed

_Baseline (v1). No prior version; this establishes the starting point for future diffs._

3. Details

Miniaturized, lower-cost ion-selective sensing

A 2026 paper reports a wafer-scale fabricated ion-selective graphene field-effect transistor (ISGFET) array with a 2 micrometer by 5 micrometer sensing area, monolithically integrating potassium, sodium and calcium-selective membranes on one chip [1] [single-source]. Its own reported performance:

"The ISGFET-based sensing platform for the first time demonstrated its 100% diagnostic accuracy for potassium measurement in human plasma with an error of 4.37% (0.17 mM), when consuming less (<30 μL) sample volume, compared to hospital-based instrumentation." — PMID 41492142

Read narrowly: this is a bench comparison against "hospital-based instrumentation" on human plasma samples, not a clinical validation study, a regulatory submission, or a device with a name — the paper reports the fabrication method and its own bench accuracy, nothing about manufacturing cost, throughput, or shelf stability.

Wearable, continuous interstitial-fluid electrolyte sensing — still preclinical

Two papers, five years apart, describe multiplexed microneedle-based potentiometric electrodes that continuously track potassium (alongside sodium, or alongside glucose and lactate) in skin interstitial fluid rather than blood [2][3] [single-source]. The earlier device was validated in "artificial ISFs" and a chicken-skin model, not in a living animal or human [2]. The newer one reports in vivo wireless monitoring in rats with "strong agreement to blood-based measurements," and separately reports "human serum analysis" — an ex vivo comparison on drawn serum, not a human wearing the device [3] [single-source]:

"Wireless in vivo monitoring in rats captured dynamic metabolic fluctuations with strong agreement to blood-based measurements, while human serum analysis demonstrated high clinical consistency across all analytes." — PMID 42641277

Neither paper is a CKD-population study, a human wearable trial, or a submission to FDA. Both are the technology category — non-blood, continuous electrolyte sensing — that would have to exist before a device like this reached the population this domain describes.

A second wave of ECG-based, non-blood hyperkalemia-screening entrants

Beyond the AliveCor/KardiaK entry already on record in the domain dossier, two further registered trials show active work on inferring hyperkalemia from ECG waveform rather than a blood draw. AccurKardia, Inc. is recruiting for a pilot study of its investigational "AK+ Guard" software as a medical device in CKD stage III-IV outpatients on RAASi therapy or with a documented hyperkalemia history, with a target (ESTIMATED, not yet enrolled) of 50 participants; the registered primary outcome is sensitivity and specificity for detecting serum potassium at or above 6.5 mmol/L against a scheduled outpatient lab draw, and no results are posted [4] [single-source · sponsor-reported]. AccurKardia's underlying platform is already FDA-cleared: the AccurECG Analysis System (K223013, decided 2023-06-23) is cleared for single-lead beat-by-beat ectopic-beat detection, heart-rate measurement and rhythm analysis on wet-electrode ambulatory ECG recordings [5]; its indications for use say nothing about potassium or hyperkalemia, which is the same pattern the domain dossier already documents for the QYE product-code family — the cleared hardware and analysis layer is general-purpose, and the hyperkalemia-inference claim is the uncleared, investigational layer sitting on top of it.

Separately, an independent, completed 32-patient study enrolled adults on maintenance hemodialysis to wear a chest-attached single-lead ECG device ("HiCardi") during dialysis sessions and correlate ECG characteristics with serum potassium over four measurement points across six weeks; the study is complete but has posted no results [6] [single-source · sponsor-reported].

FDA clearance counts: potassium electrodes up, creatinine electrodes flat

Querying openFDA's 510(k) database by product code and five-year window: the potassium ion-selective-electrode code (CEM, 21 CFR 862.1600) shows 1 clearance from 2016-01-01 through 2020-12-31 against 4 from 2021-01-01 through 2026-09-02; the creatinine enzymatic-electrode code (CGL, 21 CFR 862.1225) shows 1 clearance in each window [7][8] [single-source]. These are exact counts for the windows queried, not truncated by a result-limit cap, but the absolute numbers are small enough (1 vs. 4, and 1 vs. 1) that neither should be read as an established growth trend — a handful of clearances moving by a factor of four is exactly the kind of counted series the domain dossier already flags as unable to carry a confidence tag [inference, carried to §5].

4. Sources

[1] Wafer-Scale Fabrication of Miniaturized Graphene-Based Ion-Selective Field-Effect Transistor Chips for Clinical Plasma Test — ACS Applied Materials & Interfaces (published 2026, month not given in the PubMed record; accessed 2026-09-01). PMID 41492142 — https://pubmed.ncbi.nlm.nih.gov/41492142/ [peer-reviewed] [2] Microneedle-Based Potentiometric Sensing System for Continuous Monitoring of Multiple Electrolytes in Skin Interstitial Fluids — ACS Sensors (published 2021-06-25; accessed 2026-09-01). PMID 34038108 — https://pubmed.ncbi.nlm.nih.gov/34038108/ [peer-reviewed] [3] Electrode multiplexing enables scalable continuous molecular monitoring in interstitial fluid — Biosensors & Bioelectronics (published 2026, month not given in the PubMed record; accessed 2026-09-01). PMID 42641277 — https://pubmed.ncbi.nlm.nih.gov/42641277/ [peer-reviewed] [4] AK+ Guard Pilot Study in Chronic Kidney Disease: Outpatient Diagnostic Accuracy and Remote Monitoring — ClinicalTrials.gov (first posted 2025-10-16; accessed 2026-09-01). NCT07210021 — https://clinicaltrials.gov/study/NCT07210021 [trial-registry] [5] 510(k) AccurECG Analysis System — FDA (decision 2023-06-23; accessed 2026-09-01). K223013 — https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K223013 [federal-registry] [6] Prediction of Hyperkalemia in Dialysis Patients Through Waveform Analysis Using Wearable ECG — ClinicalTrials.gov (first posted 2026-03-20; accessed 2026-09-01). NCT07054905 — https://clinicaltrials.gov/study/NCT07054905 [trial-registry] [7] FDA 510(k) clearances, product code CEM (Electrode, Ion Specific, Potassium) — openFDA device/510k database (accessed 2026-09-01). 21 CFR 862.1600 — https://api.fda.gov/device/510k.json?search=product_code:CEM [federal-registry] [8] FDA 510(k) clearances, product code CGL (Electrode, Ion Based, Enzymatic, Creatinine) — openFDA device/510k database (accessed 2026-09-01). 21 CFR 862.1225 — https://api.fda.gov/device/510k.json?search=product_code:CGL [federal-registry]

5. Sourcing & Gaps

Well established: nothing in this report rests on two independent, non-affiliated sources — every line here is a single bench paper, a single registered trial, or a single registry query, and is marked accordingly.

Thin: all four sensor papers [1][2][3] are marked [single-source] and describe bench or animal-model work, not a human clinical study, a named product, or a regulatory filing. Both trial records [4][6] are marked [single-source · sponsor-reported] because neither has posted results — the outcomes described are what each sponsor registered to measure, not a finding. AccurKardia's target enrollment of 50 is written above as an ESTIMATED figure, not a count of anyone enrolled; the HiCardi study's 32 is the ACTUAL enrollment of a completed study that has still posted no results. The CEM/CGL clearance counts [7][8] are a single query each and are flagged in §3 as too small in absolute terms to read as a trend.

Rescoped from class 3: none in this report. Every proposition here is either a registry fact (a clearance, a trial record) or a published bench measurement, not a question about what a person would do.

Out of scope: CPT descriptors, not reproduced anywhere in this repo; fda.gov guidance documents, excluded for intermittent bot mitigation; any non-US, non-EU jurisdiction. No EU technology-clearance source (a CE-mark equivalent) was queried, since this domain's stated jurisdiction is US.

Not searched vs. not found:

• Not searched: patent filings for any of the sensor technologies named here (the patent connector resolves a single known patent number rather than searching by topic, and no specific patent number for these technologies was in hand); cost or unit-price data for any device or chip described; guideline or society statements referencing any of these technologies; individual Indications for Use PDFs for any device other than K223013.
• Not found: no human-subject clinical study of a continuous, non-blood potassium sensor (microneedle or otherwise) in a CKD or dialysis population — both interstitial-fluid papers [2][3] stop at animal-model or ex vivo human-serum validation. No FDA clearance or trial record naming a device that combines the miniaturized ISFET chip technology in [1] with a wearable or point-of-care form factor was located.

[inference] The CEM/CGL clearance-count comparison in §3 (1-to-4 vs. flat) is read here as too small to constitute a trend rather than as evidence of accelerating potassium-sensor innovation; a reader could draw the opposite conclusion from the same two numbers, which is exactly why the domain dossier's own rule treats a counted series of this size as context rather than as a claim a Verifier could stand behind.

6. Claim Candidates

Propositions a checker could attempt. This report does not append them — /research drafts them onto a candidate with engine/scripts/append_research_claims.py, which constructs the unverified tag itself.