To the Editor: Intravenous immunoglobulin preparations containing maltose (eg, Intragam P [CSL Limited]) can interfere with the readings of blood glucose monitors that use test strips with glucose dehydrogenase, such as Advantage (Roche).1 Glucose dehydrogenase is an enzyme of the Pyrroloquinolinequinone class which reacts with the disaccharide isomer maltose present in Intragam P at concentrations of 10 g/100 mL,2 resulting in falsely elevated blood glucose level results. Blood glucose monitors, such as Precision (Medisense products), Medisense (Medisense products)3 or Accutrend (Roche), that use the glucose oxidase system, do not react with maltose and can be safely used for patients receiving Intragam P.

We have had two patients in whom capillary blood glucose levels were over-estimated.

One was a 64-year-old woman with type 2 diabetes who was being treated with haemodialysis, and who received Intragam P for immune-mediated thrombocytopenic purpura. Before being admitted, her diabetes was reasonably controlled by 10 units of protophane twice daily.

She received prednisone (100 mg/day) from Day 1 to Day 13 and Intragam P intravenously each day from Day 2 to Day 6 and from Day 14 to Day 18.

While the patient was receiving Intragam P, the Advantage monitor gave persistently higher readings than both the Precision monitor and plasma glucose level measurements. The following paired readings were obtained:

• Advantage capillary glucose reading of 9.3 mmol/L while the plasma glucose level was 2.3 mmol/L; and

• Advantage capillary glucose reading of 24.4 mmol/L while the plasma glucose level was 10.4 mmol/L.

During the second course of Intragam P we noted that readings with the Precision monitor were equivalent to the measured plasma glucose level.

This patient developed hypoglycaemia because her insulin doses were increased on the basis of falsely elevated capillary glucose readings as measured on Advantage blood glucose strips. A Precision monitor was used for this patient until after the haemodialysis treatment which followed the final dose of Intragam P. After this time Advantage blood glucose readings approached those obtained with the Precision monitor.

A second patient — a 35-year-old woman who was not known to have diabetes, but was having her glucose levels monitored while undergoing total parenteral nutrition — was given Intragam P for idiopathic thrombocytopenic purpura. While receiving Intragam P, capillary glucose levels by the Advantage monitor were elevated by 13–20 mmol/L compared with concurrent (and normal) plasma glucose level measurements.

It has previously been reported that icodextrin, used in some peritoneal dialysis fluids, can have similar effects, as it is hydrolysed to oligosaccharides, including maltose, maltotriose and maltotetraose.4,5

The reaction with maltose has important clinical implications. Although it is stated in the product information for Advantage test strips that glucose readings may be affected by maltose levels over 16 mg/dL (0.89 mmol/L), clinicians may not be aware that Intragam P is in a maltose solution.

For patients receiving Intragam P, the Advantage monitor is not suitable, and the Precision, Medisense or Accutrend blood glucose monitors, which use glucose oxidase which does not react with maltose, should be used instead.

We have reported our experience to the Australian Red Cross Blood Service as an adverse event.