Our evaluation demonstrated that three ICD-9-CM case finding codes detected with high specificity nearly one-quarter of all female Oregon IPV victims aged 20–55 years estimated to have sought hospital or ED care in 2000. The addition of 12 provisional codes doubled sensitivity but reduced PVP from 95% to <50%. Highest incidence occurred in women aged 20–29 years, but hospitalization risk increased among victims who were black, aged ≥50 years, or had comorbid illness.
This study provided the first estimate of sensitivity of diagnosis codes using population-based survey data to estimate the true number of victims treated in EDs and/or hospitalized for IPV-related injuries. Although sensitivity of ED record review for other types of injuries (e.g., firearm-related) may exceed 70%,20,21
IPV is more difficult to detect because of nondisclosure from shame or fear; lack of inquiry,5
recognition, and/or proper documentation by health-care providers; and absence of discrete physical signs or specific clinical presentations. Indeed, among the survey respondents who reported seeking ED or hospital care for a past-year assault, only 56% (sexual assaults) to 74% (physical assaults) said that they had disclosed to the medical perpetrator that the injury had been perpetrated by an intimate partner. Short lists of IPV case finding questions have 65% to 71% sensitivity when compared with longer validated questionnaires in randomly selected women.22
However, this method requires that trained personnel be available to interview patients and depends upon willingness to divulge IPV in the ED setting.
Sensitivity is also affected by coding practices. Investigators elsewhere have found that both E-codes and standard ICD-9-CM codes for abuse (e.g., 995.85) are underused in IPV cases.14,23
Although case finding codes were not restricted to E-codes in this study, a single E-code (E967.3) (identifying an intimate partner as the perpetrator of an assault) identified nearly 96% of confirmed IPV cases detected using the three primary codes. However, E-code use is not mandated in Oregon, and epidemiologists have determined that an appropriate E-code is used for only 65% of injuries (Personal communication, J. Alexander, Oregon Injury Prevention Epidemiology Program, August 2004). Nonetheless, monitoring IPV using a short list of diagnostic codes appears to be a relatively sensitive and cost-efficient method of detecting trends, describing victims and perpetrators, and directing interventions to those at greatest risk for harm.
High PVP of the short list of case finding codes is not surprising because two of the codes, 995.81 (“adult physical abuse”) and E967.3 (“battering by intimate partner”) are intended for use in the setting of IPV.23
Use of 12 additional provisional codes increased sensitivity as expected, but reduced specificity to approximately 50%. Probably because of the nature of the codes involved, cases identified using the provisional codes were more likely than those identified using the three primary codes to involve a sexual assault and a primary diagnosis of something other than battering or maltreatment.
In this study, incidence of IPV leading to ED and/or hospital treatment was highest in women aged 20–29 years or black, and most assaults did not involve weapons. These findings are consistent with those of previous national surveys, including the National Violence Against Women Survey and the National Crime Victimization Survey, and medical record review of violence treated in emergency rooms.1,9,24
However, characteristics of female victims at greatest risk for hospitalization after an episode of IPV are new. Whereas overall IPV rates were highest among women aged 20–29 years, relative risk of hospitalization was significantly higher for women aged ‒50 years. Rate of hospitalization was also significantly higher for black women and for those with comorbid medical or mental illness or a drug overdose. Together, these findings support the assertion that although IPV rates decrease with age, as women age they might suffer more serious consequences when assaulted. Vulnerability to injury could explain a higher inpatient-to-outpatient-care ratio among older victims, but this association also suggests the possibility of survivor bias (i.e., those who stay with violent partners longer might risk increasingly violent assaults).
Why relative risk of hospitalization might be higher for black victims is unclear. Previous studies conflict on whether black victims are at greater risk for IPV than white victims.1,9,15
In addition to the possibility of actual differences in frequency or severity of IPV by race, this finding may reflect cultural differences in willingness to disclose or seek assistance for IPV injuries; use of the ED as a source of primary care; or social, geographic, or financial factors important in the decision to seek medical care and/or to hospitalize an IPV victim.
This study has several limitations. Small numbers of non-white and hospitalized victims precluded precise estimates of rates by race and multivariate analysis of risk factors for hospitalization. Race/ethnicity as recorded in the medical record was not uniformly determined. Sometimes, these may have been determined by patient self-report, observed by the clinician or clerk, transferred from another document, or even inferred from a surname. To the extent that ethno-racial misclassification was nonrandom, observed differences in incidence and hospitalization by race or ethnicity should be interpreted with caution. This study also lacked information about perpetrators, a general limitation shared by many IPV studies. In addition, using just three case finding codes maximized specificity but might have distorted the description of IPV victims. One 2004 study determined that the use of codes that specify the relationship to the perpetrator (e.g., E967.3), in addition to being infrequent, was also associated with patient characteristics.23
In our study, differences were observed between victims identified by the short and expanded code lists.
Also, because an agreed-upon gold standard for IPV treated in acute care hospitals was lacking, denominator estimates for sensitivity calculations were based on extrapolation from estimates obtained from a telephone survey. To the degree that respondents underreported IPV or hospital care for IPV injuries, the true number of victims seeking ED care used in the denominator of the sensitivity calculation might have been underestimated. However, the results of the 1994 national study can be used to predict a rate of 306 IPV-related injuries seen in EDs per 100,000 women aged 20–55 years and support the estimate of 276 per 100,000 Oregon women used in this study.25