Current issues of ACP Journal Club are published in Annals of Internal Medicine


Diagnosis

Hypoglycemic symptoms as a measure of low blood glucose were unreliable

ACP J Club. 1991 May-June;114:85. doi:10.7326/ACPJC-1991-114-3-085


Source Citation

Pramming S, Thorsteinsson B, Bendtson I, Binder C. The relationship between symptomatic and biochemical hypoglycaemia in insulin-dependent diabetic patients. J Intern Med. 1990;228:641-6. [PubMed ID: 2280242]


Abstract

Objective

To evaluate the accuracy of subjective feelings of hypoglycemia compared with blood sugar measurements among patients with insulin-dependent diabetes mellitus under everyday conditions.

Design

Patient self-reports of hypoglycemic symptoms were compared with capillary blood sugar test results.

Setting

Data were collected by subjects at their homes and places of work. All subjects received outpatient care at the Steno Memorial Hospital in Gentofte, Denmark.

Patients

90 outpatients with insulin-dependent diabetes were randomly selected and agreed to participate. 24 patients (27%) were noncompliant and were excluded from analysis. The 66 patients included 32 men and 34 women aged 17 to 59 years. 77% were taking insulin twice daily; the remainder were taking insulin 3 times daily.

Description of test and criterion standard

At 7 specified times during the day, patients recorded whether they felt hypoglycemic ("test") and then collected capillary blood samples that were mailed to the hospital laboratory for measurement of blood sugar concentration ("criterion standard"). These data were collected on 3 consecutive days and then weekly for 3 weeks. The predictive value of specific symptoms for biochemical hypoglycemia was not evaluated.

Main outcome measure

Hypoglycemia was defined as a capillary blood sugar concentration of < 3 mmol/L (< 54 mg/dL).

Main results

During the 4-week study period, 43 patients (65%) experienced 185 episodes of symptoms that they perceived to be caused by hypo- glycemia, but biochemical hypoglycemia accompanied only 29% of these episodes. Nearly 4% (94) of the blood samples had blood sugar concentrations in the hypoglycemic range, but patients perceived hypoglycemia for only 15 (16%) of these occasions. The risk for hypoglycemia was greatest just before lunch: 14% of all blood samples collected before lunch were hypoglycemic. When patients reported subjective feelings of hypoglycemia, the median blood sugar concentration was 3.4 mmol/L (61 mg/dL), with a broad range {10th percentile, 2.4 mmol/L [43 mg/dL]; 90th percentile, 5.4 mmol/L [97 mg/dL]}. Patients under "tight" control had more frequent episodes of biochemical hypoglycemia, but they did not have symptoms of hypoglycemia any more frequently than patients under poor control.

Conclusion

Hypoglycemic symptoms were an unreliable indicator of low blood glucose levels in outpatients with insulin-dependent diabetes.

Source of funding: Not stated.

Address for article reprint: Dr. S. Pramming, Steno Memorial Hospital, Niels Steensenvej 2, DK-2820 Gentofte, Denmark.


Commentary

Clinicians often use patients' reports of hypoglycemic symptoms to adjust insulin therapy; we tend to reduce insulin doses when patients complain of frequent feelings of hypoglycemia, and we feel comfortable when well-controlled patients with diabetes deny hypoglycemic symptoms. The results of this study call both practices into question. There appears to be a weak association between patients' perceptions of hypoglycemia and the actual blood sugar concentration, and no association between the frequency of patients' perceptions of hypoglycemia and their mean glycemic control. These results among outpatients are consistent with findings from studies of hospitalized patients (1). The lack of association probably results from several factors: The symptoms are nonspecific (hyperglycemia can even cause some of the same symptoms); hypoglycemia will often go unrecognized among patients with well-controlled glycemia because frequent episodes of hypoglycemia produce tolerance (tachyphylaxis); symptoms without actual hypoglycemia can occur among diabetic patients with poorly controlled glycemia because symptoms might be caused by the rapidity or magnitude of the reduction in blood sugar rather than by the transgression of some threshold.

This study leaves several questions unanswered. Can patients learn to interpret their symptoms better? Can physicians interpret patients' symptoms more accurately than the patients themselves? What is the harm of frequent episodes of asymptomatic hypoglycemia? The results of another study leave us with some hope (2). For individual patients, specific symptoms can be reliable markers for hypoglycemia, although tremendous variation occurs among patients on which symptoms are meaningful and which are simply "noise."

Arthur T. Evans, MD, MPH
University of North Carolina at Chapel HillChapel Hill, North Carolina, USA.


References

1. Cox DJ, Clarke WL, Gonder-Frederick L, et al. Accuracy of perceiving blood glucose in IDDM. Diabetes Care. 1985;8:529-36.

2. Pennebaker JW, Cox DJ, Gonder-Frederick L, et al. Physical symptoms related to blood glucose in insulin-dependent diabetics. Psychosom Med. 1981;43:489-500.


Author Update

New studies have pointed out the importance of previous hypoglycemic episodes for the recognition of hypoglycemic symptoms and the importance of metabolic control. Patients in strict metabolic control may have fewer symptoms or changes in symptoms caused by hyperglycemia.