SUN-568 - Pseudohypoglycemia: A Case of Unreliable Finger Capillary Glucose Readings

CASE
A 62-year-old man with history of Parkinson’s disease (PD) complicated by autonomic dysfunction, heart failure, and presumed adrenal insufficiency was admitted with altered mental status. He was found to have recurrent low point-of-care (POC) fingerstick blood glucose (FSBG) readings and a serum glucose of 54 mg/dL. Establishing Whipple’s triad was challenging due to his dementia and fluctuating mental status. However, during these hypoglycemic episodes, he was observed to become unresponsive with a rigid, flexed posture. Preliminary evaluation showed c-peptide 0.8 (1.1 – 4.4 ng/mL), insulin < 0.4 (2.6 – 24.9 uU/mL), proinsulin 2.3 (0.0 – 10.0 pmol/L), and beta hydroxybutyrate 0.10 (0.00 – 0.40 mmol/L) with concurrent serum glucose 54 mg/dL, ruling out hyperinsulinemic hypoglycemia. CT abdomen and pelvis showed no evidence of malignancy.
Over the following week, it became gradually evident that his alertness did not always improve after dextrose administration and normalization of his POC FSBG. Moreover, there were episodes during which the patient remained conversant despite extremely low FSBG readings (for example, 16 mg/dL). Additional investigation revealed significant discrepancies between his POC FSBG readings and serum glucose values, in which the former was low but the latter was greater than 100 mg/dL. Consequently, the patient was diagnosed with pseudohypoglycemia, and POC earlobe glucose testing was initiated given the unreliability of his FSBG readings.
His episodes of altered mental status were attributed to the “on–off phenomenon” of PD, and Neurology follow-up was recommended for medication optimization.

DISCUSSION
In patients with altered mental status, initial evaluation should include POC glucose testing. This patient’s POC FSBG readings often suggested hypoglycemia. However, Whipple’s triad was inconsistently met. Although his symptoms initially appeared to resolve after dextrose administration, in hindsight, this was coincidental. In this case, pseudohypoglycemia was particularly challenging to diagnose as the discordance between his POC FSBG readings and serum glucose values was not always present. It was posited that this occasional discordance in this patient without Raynaud’s or peripheral vascular disease was due to his hemodynamic lability of unclear etiology characterized by hypothermia, bradycardia and hypotension.
This case demonstrates two uncommon coexisting phenomena: altered mental status due to the “on–off phenomenon” of PD and discordant POC FSBG readings and serum glucose values. This highlights the importance of cautious interpretation of POC FSBG to prevent misdiagnosis and unnecessary evaluation and treatment. It also shows that the earlobe, while not approved for POC testing, can be a safe and alternative site for capillary glucose monitoring as seen in a few limited studies.

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