March 01, 2011
2 min read

A rollercoaster of emotions

Which blood glucose readings can be trusted?

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The vascular surgery team calls for an inpatient consult late on Friday afternoon. A 56-year-old man with a longstanding history of severe peripheral vascular disease was admitted for assessment of patency of a popliteal artery stent.

The patient does not carry a diagnosis of diabetes. However, he was noted to have a blood glucose level of 1,014 mg/dL on his serum chemistry 2 days ago. This prompted closer blood glucose monitoring, with finger sticks between 71 mg/dL and 103 mg/dL. The next morning, the patient again had blood glucose of 321 mg/dL on chemistry and normal finger sticks. The morning of the consult, the patient had blood glucose of 541 mg/dL on chemistry, which prompted the consult for diabetes.

Ronald Tamler, MD, PhD, MBA
Ronald Tamler

The patient denies polyuria, polydipsia or blurry vision, although he does have leg pain at rest and severely impaired mobility. He has a history of severe peripheral artery disease, popliteal aneurysm, gangrene, cerebrovascular accident, depression, hypertension, lower urinary tract syndrome and seizure disorder. He has no known drug allergies and is taking divalproex, tamsulosin, clonazepam, metoprolol, oral fluoxetine and subcutaneous heparin.

A “sliding scale” with insulin lispro has been started by the surgeon, but because of normal finger sticks, none has been administered so far.

Family history is negative for diabetes. The patient lives in a nursing home and quit smoking 6 months ago after 60 pack-years. He denies alcohol or recreational drug use.

On physical exam, this is a man in pain with gangrene of the second to fifth toe of the left foot and left hemiparesis; remarkably good dorsal pedal pulses bilaterally; afebrile; 77 kg; heart rate 67; and normotensive at 110/57 mm Hg. Exam is otherwise unremarkable. The patient is anxious about his possible new diagnosis of diabetes and is asking many questions about what he should or should not eat.

HbA1c is pending, and all other pertinent labs are unremarkable, with the exception of sodium levels between 122 mEq/L and 133 mEq/L.

Patient with peripheral artery disease.

Photo courtesy of: Ronald Tamler, MD, PhD, MBA

What is the best next step in the management of this patient?

A. Start IV insulin at 1 unit per hour immediately.

B. Order 2% saline solution at 50 mL per hour and leave the case for the weekend on-call team.

C. Ask the nurse to use a different glucose meter and monitor the coding process.

D. Determine whether faulty phlebotomy may have occurred.

E. Order a “preserved glucose” with the next phlebotomy.


Correct answer: D

This patient with peripheral artery disease was delighted to hear that he did not have diabetes. When our team examined the patient, we saw a phlebotomy mark upstream from the IV line (See image). In the far corner of the room was a freshly disconnected D5 infusion bag (D). This explained the unusually high blood glucose levels, as well as the patient’s persistent hyponatremia. A preserved glucose with tubes coated to prevent glycolysis is useful in settings in which false-low blood glucose levels are suspected (E). IV insulin would hopefully have been stopped by the first finger-stick measurement or else the patient would be at risk for hypoglycemia (A).

Ronald Tamler, MD, PhD, MBA, is assistant professor and Rifka Schulman, MD, is a clinical fellow, both in the division of endocrinology at Mount Sinai School of Medicine, N.Y.

Disclosures: Drs. Schulman and Tamler report no relevant financial disclosures.