The continuous glucose monitor (CGM) transformed diabetes management by converting a 4-times-daily finger stick into a continuous stream of data. CGM uptake has extended far beyond diabetes — athletes, biohackers, longevity enthusiasts, and people with prediabetes now wear CGMs to understand their metabolic responses to food, exercise, sleep, and stress. The next metabolic biomarker to get the continuous monitoring treatment is ketones — specifically beta-hydroxybutyrate (BHB), the primary blood ketone that indicates whether the body is in a state of fat-fueled ketosis.
Why Ketones Matter and Why Spot Measurement Isn't Enough
Blood ketones are relevant across multiple clinical and consumer contexts:
- Epilepsy: The ketogenic diet is an established treatment for drug-resistant epilepsy, particularly in children. Maintaining therapeutic ketosis (BHB 2–5 mmol/L) is correlated with seizure reduction. Currently, monitoring requires finger-stick blood meters 3–4 times daily — burdensome for families and poorly tolerated in children. Continuous monitoring would transform compliance tracking and therapeutic titration.
- Type 1 diabetes: Diabetic ketoacidosis (DKA) is a life-threatening emergency caused by extreme ketone elevation in the absence of insulin. Continuous ketone monitoring could detect early DKA before it reaches dangerous levels — particularly important during illness or insulin pump failures.
- Metabolic health and weight loss: Ketogenic diet adherence is binary at the metabolic level but variable at the behavioral level — small carbohydrate amounts can kick patients out of ketosis for 12–24 hours without their awareness. Continuous monitoring provides real-time feedback on diet adherence.
- Athletic performance: Fat adaptation in endurance athletes is associated with sustained power output at lower carbohydrate cost. Continuous monitoring of ketone levels during fasted training, extended exercise, or carbohydrate periodization protocols could optimize performance nutrition.
The Technology: Enzymatic Biosensors in Interstitial Fluid
Continuous ketone monitoring uses the same interstitial fluid approach as CGMs: a small subcutaneous filament sensor measures ketone levels in the fluid surrounding fat cells, which correlates with blood ketones with a 10–15 minute lag. The enzymatic chemistry differs from glucose sensing: the sensor uses beta-hydroxybutyrate dehydrogenase (HBDH) to catalyze BHB oxidation, generating an electron current proportional to BHB concentration.
The technical challenges that delayed continuous ketone monitoring beyond CGM development include enzyme stability (HBDH is less stable than glucose oxidase at body temperature), interference from acetoacetate (another ketone that cross-reacts with some sensors), and calibration drift over the 14-day sensor lifetime.
2026 Market Landscape
- Zoi (formerly Keto-Mojo): CE marked in Europe Q4 2025; FDA submission filed Q1 2026 for consumer use. 14-day sensor, Bluetooth to smartphone, BHB range 0.1–8 mmol/L. Accuracy study (n=120, 5 sites) showed MARD (mean absolute relative difference) of 11.2% vs blood meter — comparable to early CGMs.
- Nutrisense Ketone: Clinical-track device targeting epilepsy management; FDA Breakthrough Device Designation; Phase III pediatric epilepsy trial enrolling.
- Dexcom Stelo Ketone: Dexcom announced a combined glucose/ketone sensor in development; no clearance timeline provided.
Accuracy Expectations and Clinical Interpretation
A MARD of ~11% for continuous ketone monitoring compares to ~9–10% for current CGMs. For the epilepsy clinical application, this means a reading of 2.0 mmol/L might reflect true BHB of 1.8–2.2 mmol/L — acceptable for trend monitoring and alert triggering, but not sufficient to replace blood meter confirmation for clinical dosing decisions. As with CGM, accuracy at the extremes (very low <0.5 mmol/L, very high >5 mmol/L) is lower than in the middle of the therapeutic range.
Conclusion
Continuous ketone monitoring is a natural extension of the metabolic monitoring revolution that CGMs started. The clinical case is strongest for epilepsy and Type 1 diabetes DKA prevention, where continuous data would provide genuine safety improvements. The consumer case is compelling for anyone pursuing ketogenic diets or fasting protocols who currently has no real-time visibility into their metabolic state. As sensor accuracy continues to improve and costs decline, the continuous ketone monitor may follow CGM's trajectory from specialty clinical tool to consumer wellness staple. Healthcare facilities can find relevant diagnostic equipment in our catalog.
