Patients with type 1 diabetes mellitus (T1DM) may exhibit diabetic ketoacidosis (DKA) at the diagnosis. A young age (< 2 years old), diagnostic error, delayed treatment, and residence in a country with a low prevalence of T1DM are risk factors for DKA. We reviewed the medical records of 47 patients with T1DM treated at our hospital, assessed the initial results of blood gas analyses, and noted the chief complaints at the first visit. We also calculated the percentage of patients who exhibited characteristic symptoms of T1DM and noted their blood glucose, glycated hemoglobin, and blood C-peptide levels. Patients were categorized according to the severity of DKA. The chief complaints in the severe group were uncharacteristic of T1DM; therefore, T1DM was not initially suspected. These characteristic symptoms were revealed via a careful gathering of the medical history on admission. Furthermore, some patients with T1DM who had atypical symptoms of DKA and did not develop DKA were able to be diagnosed by carefully taking the medical history while considering the possibility of diabetes. In conclusion, patients with severe DKA may exhibit symptoms uncharacteristic of T1DM; however, characteristic symptoms may be revealed by carefully taking the medical history. Thus, patients with T1DM must be identified before they develop severe DKA.

Desensitization therapy for insulin allergy has been reported to rarely cause glycemic instability via the production of IgG-blocking antibodies. The present patient was a lean male with type 2 diabetes mellitus who had discontinued insulin therapy initiated at 61 years old due to insulin allergy. Because he had difficulty controlling his blood glucose without insulin therapy, he restarted it at 67 years old with an insulin preparation that did not produce an allergic reaction on a skin test. However, he again developed a local immediate-type insulin allergy. After careful continuation of insulin therapy with symptomatic treatment for the allergy, the allergy remitted, and high-titer insulin antibodies with a low affinity and high binding capacity were observed, resulting in serious hypoglycemia. In general, mild insulin allergy allows insulin therapy to be continued but may require caution, as it may cause glycemic instability due to insulin antibodies through the same mechanism as desensitization therapy.