A cautionary case history

The critical significance of the preanalytical phase of blood testing is highlighted by the tragically fatal case of an intensive-care patient who was given an inappropriately high dose of insulin following a falsely high blood glucose result. The patient was recovering from multiple organ failure following surgery in an intensive care unit where a policy of strict glycemic control with intensive insulin therapy was in force. 

On the 20th postoperative day, blood was sampled via an arterial line for routine blood glucose estimation on the blood gas analyzer sited in the unit. The result was sufficiently high (24.7 mmol/L) to warrant an increase in the rate of insulin delivery from 1 unit/hour to 10 units/hour. 

Two hours later the patient became comatose. Clinical examination suggested she might have suffered a stroke. Bedside glucometer test on a finger-prick capillary sample revealed that blood glucose was now below the detection limit of the instrument (an LO reading). 

This evidence of severe hypoglycemia prompted the insulin therapy to be stopped. Arterial blood sampled via the arterial line was taken for blood gas analysis. The glucose concentration of this sample was 10.6 mmol/L, indicating that the patient was not hypoglycemic. 

The explanation for conflicting blood glucose results was revealed when it was noted that 5 % glucose rather than 0.9 % sodium chloride solution was being used to flush the patient’s arterial line. Glucose contamination of blood collected via the arterial line led to falsely raised blood glucose concentration, inappropriate insulin therapy and severe hypoglycemia. 

Despite IV glucose therapy, which soon restored blood glucose to normal, the approximately 3-hour period of severe neuroglycopenia caused permanent brain damage and death 9 days later. In a discussion of the case history the authors describe the detailed investigation of this fatality as well as measures taken to prevent such occurrence. 

Given the now widespread use of intensive insulin therapy this case provides a cautionary warning of significance for all those involved in the care of the critically ill.