Insulin underdelivery: A frequently overlooked cause of poor glycaemic control

Recently I had a patient with insulin-treated type 2 diabetes who arrived at the consultation with the declaration “I think I’ve found out what the problem is.” I breathed a sigh of relief because for the last two years I’d groaned (hopefully internally) whenever she’d walked into the diabetes clinic. 

She had resisted insulin therapy for years despite ghastly control on everything else we had thrown at her. Initially she did reasonably well on a twice-daily fixed mixture of soluble and isophane human insulin, but she admitted to a mild needle phobia and, unbeknownst to me, had been switched to guarded insulin pen needles. The dose of insulin was cranked up but her HbA_1c continued to rise. Following an admission to hospital with urosepsis, she became repeatedly hypoglycaemic when nursing staff administered her usual insulin dose. I suspected insulin omission at home but she, her husband and her daughter all strongly denied this. Her HbA_1c remained above 100 mmol/mol (11.3%) and the same thing happened during her next admission.

It was only when the locum GP gave her the wrong pen needles and she started having repeated hypos at home that the penny dropped. Whatever she had been doing previously had resulted in non-delivery of part or all of her insulin doses. She had to reduce her dose by 60% and thereafter her HbA_1c fell to a passable 68 mmol/mol (8.4%).

The paper by Joubert et al (summarised alongside) illustrates another potential cause of insulin underdelivery – withdrawing the needle from the skin too soon after the injection – and illustrates the importance of both teaching and observing insulin injection technique. Lipohypertrophy, wrong-sized needles, premature insulin withdrawal and difficulties with plunger depression all contribute to the vagaries of insulin action and should be considered by all healthcare professionals when contemplating causes of inadequate diabetes control. This is an important but often overlooked factor.

To read the article summaries, please download the PDF