Dear Editor,

We enjoyed the article on practical management of hyperinsulinism by Aynsley-Green et al.[1] The article re-emphasises the importance of accurate measurement of blood glucose and insists on an accurate laboratory method and not a bedside screening test for diagnosing hypoglycaemia. In certain situations, the use of a bed-side test will be unavoidable, eg, if there will be a long delay before a laboratory result can be obtained, in general practice, home visits or during transport. In many hospitals bed- side tests are used to identify high-risk babies with suspiciously low values who need accurate laboratory measurements of blood glucose.

Most rapid bedside blood glucose measuring devices have been validated in the range above 2.6 mmol/L, using adult blood. We conducted a study to test the accuracy of 2 commonly used bedside methods of glucose estimation in the clinically important range of 0.5 - 4 mmol/L, using neonatal cord blood with a haematocrit over 0.5.

Cord blood samples were allowed to stand for varying periods of time to allow the glucose levels to fall in the range of 0.5 - 4mmol/L. 103 samples were analysed simultaneously in duplicate by a) Cobas hexokinase method in the laboratory, b) Hemacue and c) Precision Q.I.D.

Using the laboratory hexokinase method as the standard, the sensitivity and specificity of Precision Q.I.D. for detecting hypoglycaemia (blood glucose less than 2.6mmol/L) were 86% and 89% respectively; and for Hemacue were 83% and 100%. On average, blood glucose by Precision Q.I.D. was 0.21 mmol/L (standard deviation 0.32 mmol/L) higher than the hexokinase method on paired samples in this low range. Blood glucose by Hemacue was on average 0.34 mmol/L (standard deviation 0.23 mmol/L) higher than the hexokinase method.

Both these bedside methods tend to slightly overestimate the blood glucose in relation to the standard laboratory method. Our study suggests that in situations where bedside glucose is the only available estimate of blood glucose, a value of over 3.0mmol/L would be needed to confidently exclude hypoglycaemia.

Nilesh Mehta
Clinical Fellow, Paediatric Intensive Care Unit
St. Mary's Hospital, London W2, UK

Janet Stone
Principal Clinical Scientist in Paediatrics
Bristol Royal Infirmary, Bristol BS2, UK

Andrew Whitelaw (author for correspondence)
Professor of Neonatal Medicine
St. Michael's Hospital, Bristol BS2, UK

Reference
(1) Aynsley-Green A, Hussain K, Hall J et al. Practical management of hyperinsulinism in infancy. Arch Dis Child 2000;82:F98-107.

We read with great interest the consensus article on the investigation and management of hyperinsulinism in infancy (1). The authors discuss the value of the intra-arterial calcium stimulation test, but speculate that there is a significant risk of bowel infarction.

Intra-arterial calcium stimulation for localisation of insulinomas in adult patients has been described by several authors (2,3,4). To our knowledge, bowel infarction has never been reported as a complication.

We have used the intra-arterial calcium stimulation test in infants with hyperinsulinism to localise the site of hypersecretion of insulin, and to determine whether it is focal or diffuse (5). In six procedures performed on children (age range 2 months to 3 years) there has been no clinical or radiological evidence of bowel ischaemia or infarction, and no evidence of arterial spasm has been demonstrated on coeliac or mesenteric arteriograms.

We conclude that this is a safe and valuable investigation, and we believe that it is less invasive than the alternative technique of transhepatic portal venous sampling.

L J Abernethy Consulatant Paediatric Radiologist G L Lamont Consultant paediatric Surgeon D C Davidson Consulatant Paediatrician

References:

1. A Aynsley-Green, K Hussain, J Hall, J M Saudubray, C Nihoul-Fékété, P De Lonlay-Debeney, F Brunelle, T Otonkoski, P Thornton, and K J Lindley Practical management of hyperinsulinism in infancy Arch. Dis. Child. Fetal Neonatal Ed. 2000; 82: F98-F107

2. Doppman JL, Miller DL, Chang R, Shawker TH, Gorden P, Norton JA. Insulinomas: localization with selective intra-arterial injection of calcium. Radiology 178: 237 - 241.

3. O'Shea D, Rohrer-Theurs AW, Lynn JA, Jackson JE, Bloom SR Localization of insulinomas by selective intaarterial calcium injection. J Clin Endocrinol Metab 1996 81: 1623-7.

4. Pereira PL, Roche AJ, Maier GW, Huppert PE, Dammann F, Farsworth CT, Duda SH, Claussen CD. Insulinoma and islet cell hyperplasia: value of the calcium intarterial stimulation test when finding of other preoperative studies are negative. Radiology 1998: 206: 703-9.

5. Abernethy LJ,Davidson DC, Lamont G, Shepherd RM, Dunne MJ Intra-arterial calcium stimulation test in the investigation of hyperinsulinaemic hypoglycaemia. Arch Dis Child 1998; 78:359-63