After applying our exclusion criteria, 18,717,906 (50.2%) adult hospitalization records remained in our study sample. Among these, we identified 1,891 hospitalizations among adult patients with DM and 18,716,015 hospitalizations among adult patients without DM.

The characteristics of adult hospitalizations by whether DM was recorded as a discharge diagnosis were shown in Table 1. Compared with adult hospitalizations among patients without DM, a higher percentage of adult hospitalizations among patients with DM were white and insured by Medicaid. There were no statistically significant differences in the year of admission and hospital bed size between adult hospitalizations with and without DM diagnosis. The mean length of stay (4.8 vs. 4.1 days) and total costs ($13,241 vs. $11,458 in 2014 dollars) were higher for adult hospitalizations among patients with DM. A total of 1,891 hospitalizations without DM were successfully matched to 1,891 hospitalizations with DM based on the similarity of their propensity scores, indicating comparable demographic and hospital characteristics.

The relative risk for each of the 44 clinical conditions accounting for 5% or more of the hospitalizations among adult patients with DM were shown in Figure 1 (for exact numbers refer to Table S1 in the Supplementary Material online). Twenty-five conditions were more likely to be recorded as discharge diagnoses on hospitalizations among adult patients with DM, as indicated by a relative risk significantly greater than 1, in comparison to hospitalizations among adult patients without DM. For example, hospitalizations among adult patients with DM were more than 4 times as likely to having co-occurring conduction disorders recorded as hospitalizations among adult patients without DM. Twelve conditions were equally likely to be recorded as discharge diagnoses in hospitalizations among adult patients with and without DM, such as diabetes mellitus without complications. Eight clinical conditions were more likely to be discharge diagnoses for hospitalizations among adult patients without DM, such as essential hypertension.

Gender differences for the selected 44 clinical conditions by DM status among these 3,782 matched adult hospitalizations were shown in Figures 2 and 3 (for exact numbers refer to Table S2 online). Compared with hospitalizations among adult male patients with DM, hospitalizations among adult female patients with DM were more likely to have 11 conditions recorded as discharge diagnoses, such as thyroid disorders. Conversely, when compared with hospitalizations among adult female patients with DM, hospitalizations among adult male patients with DM were more likely to have 8 conditions recorded as discharge diagnoses, such as conduction disorders.

For more than half of the 44 examined discharge diagnoses, there were no significant gender differences among hospitalized adult patients with and without DM. Of the discharge diagnoses that adult female patients with DM are more likely to have than their male counterparts, only 3 did not have elevated risks in hospitalizations among female patients without DM. These included nonspecific chest pain, bacterial infection (unspecified site), and complications of surgical procedures or medical care. Of the discharge diagnoses that adult male patients with DM were more likely to have than their female counterparts, only 2 were specific to DM: intestinal obstruction without hernia and other upper respiratory disease.

The high rate of Medicaid usage reflected the overall morbidity among DM patients. The differences in length of stay and total costs in adults with or without DM reflected the overall severity of DM; patients with DM were more likely to have longer and more expensive hospitalizations than patients without DM. Investigation of the conditions co-occurring with DM hospitalizations revealed the multisystem nature of the condition, including cardiac, respiratory, and gastrointestinal dysfunctions. These findings were consistent with previous findings such as those reported for a Utah population.¹⁴

We found some conditions for which the gender differences in hospitalizations in adult patients with DM were larger compared with the gender differences observed in hospitalizations in adult patients without DM. For example, nonspecific chest pain was more often a discharge diagnosis among adult female DM patients than among adult male DM patients. In comparison, there was no significant gender difference in discharge diagnosis of chest pain among adult patients without DM. Such differences may indicate gender-oriented care management. However, in more than half of the co-occurring conditions, the relative risks did not differ by gender. For the most part, the gender differences observed among adult patients with DM were also observed among hospitalized adult patients without DM. Thus, the results highlight the importance of comprehensive and coordinated care for DM rather than gender-oriented care management in the inpatient setting. Previous studies mainly focused on clinic outpatient care and found gender differences in some conditions in clinically confirmed DM1 or DM2 cases.^4–6 Our study focused on the inpatient setting and used a different case identification strategy via ICD-9 codes. Thus, our results were not directly comparable to those from the earlier studies.

This study has limitations. We relied on ICD-9 codes to identify DM (code 359.21). This DM code does not distinguish DM1 and DM2, thus limiting our ability to investigate gender differences separately by type of DM. Second, some states in the NIS did not report all of their diagnosis codes. It is possible that some conditions were underreported if their ICD-9 codes were not recorded. In addition, women were found to have more “nonspecific chest pain.” This illustrates the limited usefulness of ICD diagnosis codes, as this is a symptom more than a diagnosis. Continued outpatient work-up may have demonstrated occult cardiac arrhythmias as a cause, among others. Third, we focused on conditions that accounted for at least 5% of hospitalizations among adult DM patients for sample size considerations; thus, we excluded infrequent conditions, such as cancer.^15,16 Studies have shown that malignancies are more common in the DM population with gender-specific forms of malignancies. Fourth, the analysis was based on hospitalization data, so we were unable to examine gender differences in clinical conditions treated in outpatient settings, such as obesity. Fifth, 1 patient could contribute to multiple hospitalizations in the data set. Therefore, the gender differences in hospitalizations and rehospitalizations could not be distinguished. Last, we excluded hospital transfer or hospitalizations resulting in death. We excluded transfer patients to better capture the complete hospitalization care. Deaths were excluded because hospitalizations resulting in death may have differed from those for regular hospital care. However, a French study demonstrated higher mortality in men with DM1.⁴ Future studies could investigate whether mortality and causes for mortality differ by gender among patients with DM.

In conclusion, using a national U.S. hospitalization database, we found that hospitalizations in adult patients with DM were significantly longer and more costly than hospitalizations in adult patients without DM. Among the extensive list of multisystem co-occurring conditions for hospitalized adult patients with DM, the relative risks for more than half of these conditions did not differ by gender. Most discharge diagnoses that differed by gender among adult patients with DM also showed a gender difference among comparable adult patients without DM.