Artifactual hypoglycemia: When there’s a problem in the tube

I recently was contacted by my nurse to schedule follow-up for a patient of mine whose routine labs sent by his cardiologist showed a blood glucose of 48 and a potassium of 5.8. He did not have diabetes, was not on any medications that could cause hyperkalemia, and most importantly he was asymptomatic when the labs were drawn.

Dr. Douglas Paauw

If you are looking for zebras you might consider adrenal insufficiency, which could cause both hyperkalemia and hypoglycemia, but this would make no sense in someone asymptomatic.

This pattern is one I have seen commonly when I am on call, and I am contacted about abnormal labs. The lab reported no hemolysis seen, but this is the typical pattern seen with hemolytic specimens and/or specimens that have been held a long time before they are analyzed.

Lippi and colleagues reported on the clinically significant increase in potassium in samples that visually appeared not to be hemolyzed.¹ Hemolyzed specimens can also drop glucose values, but not as profoundly as raising potassium values. When left unprocessed, glycolysis occurs in the white blood cells of a blood sample and may consume 5%-7% of the sample’s glucose content per hour.²

Khaled and colleagues looked at the drop in glucose levels in samples over time based on what anticoagulants were used.³ They found that, at 3 hours, glucose measurements were decreased by 28.4 mg/dL when sodium citrate is used, 58 mg/dL when EDTA was used, 15.4 mg/dL when fluoride oxalate was used, and 60.2 mg/dL when no anticoagulant is used.

Low blood sugars caused by elevated WBCs in blood samples has been well described.⁴ It has been described with moderate and very high WBC counts, as well as with the leukocytosis seen with polycythemia vera.⁵ The term “leukocyte larceny” has been used to describe high WBC counts that can not only utilize glucose, but also oxygen.

Saccheti and colleagues described a patient with a WBC greater than 500,000 who had repeatedly low oxygen levels on blood gases, that did not correlate with the normal oxygen saturations measured by pulse oximetry.⁶ This same issue has been seen in patients with extreme thrombocytosis.⁷Pearl: When labs don’t make sense clinically, always look at the possibility that there may be a problem in the tube and not in the person. Especially think of this when blood samples may have been held for a long time before they are run, such as with visiting nurse visits and blood draws at shelters and nursing homes.

Dr. Paauw is professor of medicine in the division of general internal medicine at the University of Washington, Seattle, and serves as third-year medical student clerkship director at the University of Washington. He is a member of the editorial advisory board of Internal Medicine News. Dr. Paauw has no conflicts to disclose. Contact him at imnews@mdedge.com.

References

1. Lippi G et al. Clin Chem Lab Med. 2006;44(3):311-6.

2. Mikesh LM and Bruns DE. Clin Chem. 2008 May;54(5):930-2.

3. Khaled S et al. Al-Mukhtar Journal of Sciences. 2018;33(2):100-6.

4. Goodenow TJ and Malarkey WB. JAMA. 1977;237(18):1961-2.

5. R Arem et al. Arch Intern Med. 1982 Nov;142(12):2199-201.

6. Sacchetti A et al. J Emerg Med. 1990;8:567–569.

7. A Mehta et al. Eur Respir J. 2008 Feb;31(2):469-72.