FDA Cites O.N. Diagnostics, LLC in 2026-09-01 Warning Letter — Medical Device Reporting/Misbranded
Letter issued · posted to fda.gov .
Subject as published: Medical Device Reporting/Misbranded
TL;DR
At a glance: The FDA's Center for Devices and Radiological Health issued a warning letter (CMS 730301) to O.N. Diagnostics, LLC on September 1, 2026, citing violations related to the VirtuOst VFA 3.0.0 software, a device cleared under K171435 for analyzing CT scans to diagnose vertebral fractures and assess osteoporosis risk. The letter identifies the device as adulterated and misbranded because version 3.0.0 introduced three significant changes without new premarket notification: a new machine learning algorithm for vertebral landmarking, migration from desktop to web-based architecture (expanding cybersecurity vulnerabilities), and platform technology migration requiring comprehensive re-verification and re-validation—all of which could significantly affect safety or effectiveness. The FDA requests O.N. Diagnostics cease commercial distribution of VirtuOst VFA 3.0.0 pending submission of required premarket notification documentation.
Argus analysis
# FDA Warning Letter Analysis: O.N. Diagnostics, LLC
**Company and Findings**
O.N. Diagnostics, LLC, a Berkeley, California manufacturer of diagnostic software, received a Warning Letter from FDA's Center for Devices and Radiological Health on September 1, 2026, following an inspection conducted March 12–17, 2026. The company produces VirtuOst and VirtuOst Vertebral Fracture Assessment (VFA) software, which analyzes medical images to diagnose vertebral fractures and manage osteoporosis. FDA determined the VirtuOst VFA 3.0.0 version is both unapproved and misbranded, triggering enforcement action.
**Regulatory Citations and Violations**
The primary violations cite 21 CFR 807.81(a)(3)(i) and related sections of the Federal Food, Drug, and Cosmetic Act. The company introduced software version 3.0.0 with substantial changes—a new machine learning algorithm for vertebral landmarking, migration from desktop to web-based architecture, and a technology platform transition—without submitting a new 510(k) premarket notification. These modifications significantly affect device safety and effectiveness by introducing new cybersecurity risks and requiring comprehensive software revalidation. Additionally, FDA cited Quality Management System Regulation violations (21 CFR Part 820) for deficient corrective and preventive action (CAPA) procedures, including delayed corrective actions, unclear CAPA-triggering criteria, and inadequate documentation of corrective action effectiveness.
**Response Timeline and Industry Monitoring Points**
FDA requested that O.N. Diagnostics cease commercial distribution of VirtuOst VFA 3.0.0 immediately. Compliance officers in medical device software should monitor whether the company submits a new 510(k) or pursues premarket approval, files a closure response addressing QMS gaps, and whether FDA issues any follow-up enforcement actions. The structural changes to the CAPA procedure—particularly narrowed triggers—may warrant scrutiny in peer firms using similar risk-assessment frameworks.
Severity context
High severity. Typically QSR / device CGMP, adulterated-drug, or significant labeling matters — usually drives a documented corrective and preventive action (CAPA) program.
Regulatory background
Medical device Warning Letters typically combine QSR observations (21 CFR Part 820) with adulteration (21 USC 351) or misbranding (21 USC 352). Post-market surveillance and MDR reporting (21 CFR Part 803) are recurring subjects.
What peer compliance teams typically do next
Most compliance officers at peer companies use a Warning Letter against a named entity as a checklist for their own CAPA program. Common steps: pull the verbatim FDA letter; map each cited 21 CFR section against the team’s SOP library; confirm CAPA coverage; brief the QMR (Quality Management Review) on whether the cited subject matter is in scope for the next internal audit. The 15-business-day response window applies to the cited entity, not to peers — but a documented internal review against the cited subjects is what regulators expect to see if a peer is later inspected on the same topic.
Excerpt from the FDA Warning Letter (public domain, 17 USC §105)
WARNING LETTER O.N. Diagnostics, LLC MARCS-CMS 730301 — September 01, 2026 More Warning Letters Warning Letters About Warning and Close-Out Letters Delivery Method: VIA Electronic Mail Product: Medical Devices Recipient: Recipient Name Shui Wong Recipient Title CEO O.N. Diagnostics, LLC 1936 University Ave, Ste 280 Berkley , CA 94704 United States (b)(6), (b)(7)(C) Issuing Office: Center for Devices and Radiological Health United States WARNING LETTER CMS 730301 9/1/2026 Dear Ms. Wong, During an inspection of your firm located in Berkley, CA, from March 12-17, 2026, investigators from the United States Food and Drug Administration (FDA) determined that your firm manufactures (or markets) the VirtuOst and VirtuOst Vertebral Fracture Assessment (VFA) software products. Under section 201(h) of the Federal Food, Drug, and Cosmetic Act (the Act), 21 U.S.C. § 321(h), these products are devices because they are intended for use in the diagnosis of disease or other conditions or in the cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body. The VirtuOst and VirtuOst VFA software products are device software functions because they analyze medical images for use in the diagnosis of existing vertebral fractures and the management of osteoporosis. As such, your firm has responsibility for maintaining full compliance with all applicable pre- and post-market requirements associated with these device software functions. Unapproved Device Violation(s) Our inspection revealed that the VirtuOst VFA 3.0.0 is adulterated under section 501(f)(1)(B) of the Act, 21 U.S.C. § 351(f)(1)(B), because your firm does not have an approved application for premarket approval (PMA) in effect pursuant to section 515(a) of the Act, 21 U.S.C. § 360e(a), or an approved application for an investigational device exemption (IDE) under section 520(g) of the Act, 21 U.S.C. § 360j(g) for the device as described and marketed. The VirtuOst VFA 3.0.0 is also misbranded under section 502(o) of the Act, 21 U.S.C. § 352(o), because your firm introduced or delivered for introduction into interstate commerce for commercial distribution this device with changes or modifications in the device that could significantly affect the safety or effectiveness of the device without submitting a new premarket notification to FDA as required by section 510(k) of the Act, 21 U.S.C. § 360(k), and 21 CFR 807.81(a)(3)(i). Specifically, the VirtuOst VFA was cleared under K171435 with the following indications: VirtuOst VFA uses sagittal sections from a spine-containing CT scan, with or without contrast enhancement, to visualize and measure vertebral deformities, classify the type and grade of any existing vertebral fracture, and from this identify patients at high risk of a future osteoporosis-related fracture. This information can be interpreted by a physician to diagnose existing vertebral fractures and to manage patients for osteoporosis. A review of the Sof…
Excerpt only. The full verbatim Warning Letter is the source of truth — always read the original before regulatory decisions.
The verbatim FDA Warning Letter is the source of truth. Always read the original before acting on any analysis or summary on this page.
Read the full letter on fda.gov ↗Frequently asked questions
- When did FDA issue the warning letter to O.N. Diagnostics, LLC?
- FDA issued the letter (MARCS-CMS 730301) on 2026-09-01 and posted it publicly on fda.gov on 2026-10-06.
- Is the FDA warning letter to O.N. Diagnostics, LLC publicly available?
- Yes. The full verbatim letter is published at fda.gov. Argus HQ links directly to the source: https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/diagnostics-llc-730301-09012026.
- What does a "high" severity rating mean for this letter?
- High severity. Typically QSR / device CGMP, adulterated-drug, or significant labeling matters — usually drives a documented corrective and preventive action (CAPA) program.
- What is the regulatory background for a Medical device warning letter?
- Medical device Warning Letters typically combine QSR observations (21 CFR Part 820) with adulteration (21 USC 351) or misbranding (21 USC 352). Post-market surveillance and MDR reporting (21 CFR Part 803) are recurring subjects.
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methodology
The analysis above is produced by Anthropic Claude Haiku 4.5 against the verbatim FDA Warning Letter excerpt and is brand-voice lint-checked before publish. The TL;DR is the same summary that ships in the customer email digest. Severity is auto-classified by Argus from the subject string and letter body using rules documented in lib/ingestion/fda-warning-letters.ts.
Argus HQ is informational only. Summaries and analyses are AI-generated and may contain errors, misclassifications, or omissions. Verify against the FDA source URL above. Argus HQ is not a law firm, accounting firm, or regulatory agency, and provides no legal, accounting, financial, medical, or regulatory advice.
Compiled by Argus HQ Research from FDA primary sources · Reviewed by Andy Gaber, Founder
Cite this record
Reusing this data in reporting or research? Here’s a ready-made citation.
Argus HQ Research (2026). FDA Cites O.N. Diagnostics, LLC in 2026-09-01 Warning Letter — Medical Device Reporting/Misbranded. Digital Empire Holdings LLC. Retrieved from https://argushq.ai/fda/warning-letter/fda-wl-o-n-diagnostics-llc-2026-09-01-medical-device
"FDA Cites O.N. Diagnostics, LLC in 2026-09-01 Warning Letter — Medical Device Reporting/Misbranded." Argus HQ Research, Digital Empire Holdings LLC, 2026, argushq.ai/fda/warning-letter/fda-wl-o-n-diagnostics-llc-2026-09-01-medical-device.
Argus HQ Research. "FDA Cites O.N. Diagnostics, LLC in 2026-09-01 Warning Letter — Medical Device Reporting/Misbranded." Digital Empire Holdings LLC. Accessed October 7, 2026. https://argushq.ai/fda/warning-letter/fda-wl-o-n-diagnostics-llc-2026-09-01-medical-device.
@misc{argushq_argushq_ai_fda_warning_letter_fda_wl_o_n_diagnostics_llc_2026_09_01_medical_device_2026,
title = {FDA Cites O.N. Diagnostics, LLC in 2026-09-01 Warning Letter — Medical Device Reporting/Misbranded},
author = {{Argus HQ Research}},
year = {2026},
publisher = {Digital Empire Holdings LLC},
url = {https://argushq.ai/fda/warning-letter/fda-wl-o-n-diagnostics-llc-2026-09-01-medical-device},
note = {Accessed: October 7, 2026}
}