Raised blood glucose during acute illness and risk of subsequent diabetes

Increased blood glucose (hyperglycemia) is a common finding among patients with acute medical conditions or trauma that warrant admission to medical wards or intensive care. In some cases this hyperglycemia is due to previously diagnosed type 1 or type 2 diabetes, but for the majority it is a consequence of the stress associated with illness/trauma. 

This so-called ”stress hyperglycemia” results from release of counter-regulatory hormones (glucagon, cortisol, epinephrine) that oppose the action of insulin. They are released as part of the physiological ”stress” response to the severe illness or trauma. With effective treatment of the illness/trauma, counter-regulatory hormone release ceases, hyperglycemia resolves, and blood glucose soon returns to normal.

For some patients with apparent ”stress hyperglycemia”, the increase in glucose concentration, or at least part of the increase, may be due to incipient type 2 diabetes that will, at some point in the future, become clinically manifest. A recently published Scottish study sought to examine the relationship between blood glucose concentration at admission to hospital and future risk of type 2 diabetes.

Researchers responsible for the study, based at Centre for Population Health Sciences in Edinburgh, Scotland, exploited two national databases of patient information that use the same unique patient identifier. The first of these databases relates to hospital admissions in Scotland and contains laboratory test results; the second is a national register of all diagnosed diabetic patients that includes clinical detail and, importantly for this study, date of diagnosis.

From the first database 141,000 adult patients (>40 years) admitted to hospital were identified. The diabetes database revealed that 18,689 of these patients were diagnosed with diabetes either before admission to hospital or within 30 days of discharge. 

These diabetic patients were excluded from study, leaving 122,000 non-diabetic patients of whom 35,367 had no blood glucose concentration recorded and were therefore excluded from the study. 

The final study population then comprised 86,634 who did not have diabetes at the time of admission but did have an admission blood glucose concentration recorded. Subsequent interrogation of the diabetes database revealed that of the 86,634 study patients, 1952 (2.3 %) developed type 2 diabetes during the 3 years after discharge from hospital.

The overall 3-year risk of developing diabetes was thus 2.3 %, but differed depending on admission blood glucose concentration. Calculated 3-year risk of type 2 diabetes was found to rise linearly from <1 % for those whose admission blood glucose was ≤5.0 mmol/L to 15 % for those whose blood glucose was 15.0 mmol/L. 

Risk was found to plateau at 15 % for glucose concentration >15 mmol/L. Gender and age were found to affect risk. At every level of glucose concentration the risk was found to be higher for males than for females. Risk was higher for a given glucose concentration among those aged 50-69 years but lower for those younger and older than this. 

Taking gender and age into account, highest risk of type 2 diabetes occurring during the following 3 years was found to be among 55- to 60-year-old males whose admission blood glucose concentration is equal to or greater than 15.0 mmol/L; for this particular subset of patients the calculated risk is 25 %.

The team responsible for this study have produced a diabetes risk calculator (available at www.cphs.mvm.ed.ac.uk/diabetes-risk/) based on their study findings, that allows input of age, gender and hospital admission blood glucose concentration and output of the % risk of type 2 diabetes occurring during the following 3 years.

This can help clinicians to advise those patients with raised blood glucose concentration during admission to hospital about their future risk of diabetes and the need for close monitoring of blood glucose and appropriate lifestyle modification to prevent or delay diabetes onset. 

The authors of this study suggest that patients with blood glucose greater than 11 mmol/L, which according to their study is associated with a 3-year risk of 10 % (5-fold higher than the risk in the general population), should be offered follow-up testing.

The study has demonstrated that, though transitory in nature, apparent stress hyperglycemia can have long-term significance.