# The Diabetic Hand as a Diagnostic Blind Spot: A Case of Severe Pseudohyperglycemia Masking Critical Hypoglycemia

## TL;DR

A diabetic patient's hand conditions caused misleadingly high blood sugar readings, hiding a dangerous low blood sugar level, highlighting a critical diagnostic risk.

## Contribution

Identifies a novel failure mode in point-of-care glucose monitoring due to diabetic hand syndromes.

## Key findings

- Bilateral carpal tunnel syndrome and hand osteoarthritis caused pseudohyperglycemia in a diabetic patient.
- Venous blood testing revealed critical hypoglycemia despite persistently high capillary readings.
- The diabetic hand can invalidate standard glucose monitoring, requiring routine hand assessment and venous verification.

## Abstract

Carpal tunnel syndrome (CTS) and hand osteoarthritis (OA) are prevalent, painful comorbidities in diabetes mellitus. While their symptomatic burden is recognized, their potential to create critical diagnostic blind spots by compromising point-of-care glucose monitoring is an underappreciated patient safety hazard. These conditions can compromise the local capillary bed through nerve compression, joint inflammation, and microvascular dysfunction, thereby invalidating the core physiological assumption of point-of-care glucose monitoring: that a fingertip sample accurately reflects systemic glucose levels.

An 80-year-old woman with type 2 diabetes presented for knee surgery. A routine postoperative capillary blood glucose (CBG) check yielded a value of 23 mmol/L, triggering a protocol for insulin administration. As the patient was asymptomatic, clinical suspicion led to a venous blood glucose test, which revealed hypoglycemia at 2.5 mmol/L. A systematic, multi-step verification was performed: the device was recalibrated, a repeat CBG from a different site on the same hand was obtained, and a second glucometer of a different brand was used to test both the ipsilateral and contralateral hands. All point-of-care readings remained persistently elevated (23-24 mmol/L), confirming a reproducible physiological error. A subsequent physical examination identified previously undiagnosed bilateral CTS and severe hand OA, pathologies constituting a "diabetic hand" with compromised peripheral perfusion.

This near-miss event presents a critical paradox: severe pseudohyperglycemia in a setting where classic physiology predicts the opposite artifact. The finding persisted despite the exclusion of common technical errors, underscoring a novel and dangerous failure mode associated with the compromised diabetic hand. The case demonstrates that such hand syndromes can catastrophically invalidate point-of-care glucose monitoring. It argues for the routine assessment of hand pathology in diabetic patients and warrants immediate venous verification of any clinically discordant point-of-care result to prevent catastrophic error.