The availability of ICD codes, by which we mean the proportion of patients being seen in a region for which ICD codes are available, in general is poorly understood. ICD coding of chief complaints is uncommon. ICD coding of ED diagnoses by clinicians using clinical information systems is not universal. Nationwide, only 17% of physician practices and 31% of EDs have even adopted point-of-care systems (Burt and Hing, 2005). ICD codes from healthcare-insurance claims data are widely available, but the time latency is too long for many biosurveillance applications.
We discuss the empirical data about time latency from published reports shortly. But it is worthwhile to review the steps in the process of assigning ICD codes and transmitting them to a biosurveillance system (Figure 23.1), and how these steps may contribute to time latency. First, an individual clinician or coder must acquire enough information about a patient to assign an ICD code. This individual may be a triage nurse who obtains the patient's chief complaint within minutes of the patient's arrival to the ED, or a professional coder who studies a four-inch thick medical record weeks after the patient left the hospital. Next, someone must enter an ICD code into a computer system.11 For physician-assigned ICD codes, that may occur within minutes after she sees the patient (which in turn may be minutes to hours after the patient arrived at the office or ED) or even hours or days after the patient leaves the office or ED. Finally, the computer system must transmit the codes to a biosurveillance system or other computers that in turn transmit them to a biosurveillance system. Systems may either transmit ICD codes in real time (the exception) or in batch mode (the rule). Ideally, studies of ICD codes would measure and report the contribution of each step to overall time latency.
Studies to date—with one exception we discuss below—have not measured time latencies involved in ICD-code monitoring. Instead, authors provide general statements such as most records were received by the next day.
Lewis et al. (2000) report a one- to three-day time latency for diagnoses encoded with ICD by physicians working at DoD clinics. They state that this latency is from the time of the patient visit to the time data are available for viewing and analysis in the ESSENCE biosurveillance system. They note two factors that affect this time latency: time delays prior to physicians assigning codes and frequency of data transmission to ESSENCE from the DoD's Ambulatory Data System.
Note that the CDC's BioSense biosurveillance system receives the same ICD codes that Lewis and colleagues studied. Anecdotally, the time latency of ICD codes obtained by BioSense is not short enough to meet the needs of some state and local public health officials (U.S. Government Accountability Office, 2005). Such anecdotes highlight the importance of accurate measurements of each contribution to time latency and detailed descriptions of who assigns ICD codes and how and when.
Reports by the National Bioterrorism Syndromic Surveillance Demonstration Program suggest that the time latency of ICD codes assigned by physicians using a point-of-care system in an outpatient setting are "usually'' less than 24 hours (Yih et al., 2004, Lazarus et al., 2002, Miller et al., 2004). This program involves multiple healthcare providers and health plans; thus, each healthcare system may have different latencies. Lazarus and colleagues report that at Harvard Vanguard Medical Associates in Boston, Massachusetts, ICD-coded diagnoses are available for "essentially all episodes by the end of the same day on which care is given'' (Lazarus et al., 2002). Miller and colleagues report that at HealthPartners Medical Group in the Minneapolis-St. Paul region of Minnesota, ICD-coded diagnoses are available "within approximately 24 hours of a patient's initial visit'' (Miller et al., 2004). Yih and colleagues report that, for the Demonstration Program as a whole, providers usually enter ICD-coded diagnoses into a point-of-care system on the same day as the patient visit, and that the systems put in place by the Program extract these data on a nightly basis (Yih et al., 2004).
Beitel and colleagues report that ED physicians at Boston Children's' Hospital code diagnoses with ICD within "hours'' of the visit (Beitel et al., 2004). They do not describe how available these data are for biosurveillance nor whether they are transmitted in real time or via a daily batch-mode process. They also report that billing administrators assign "the final ICD-9 code to all charts, usually within 48 to 72 hours.''
Suyama and colleagues report that billing ICD codes at the ED of University Hospital (which is part of the University of Cincinnati Medical Center) are available within 12 hours from the time the patient leaves the ED (Suyama et al., 2003).They do not state who assigns the ICD codes to each visit.
Begier and colleagues report that two community hospitals in the National Capital Region do not assign any ICD codes to patient visits within 24 hours of the patient leaving the ED (Begier et al., 2003). Whether ICD codes are available after 24 hours of the patient leaving the ED, they do not say.
Espino and colleagues conducted the only study that measured and reported time latencies for ICD codes (Espino and Wagner, 2001b). It is important to note that this study was of an atypical health system that expended effort to make physician-assigned ICD codes available to a biosurveillance system in real time, instead of using daily batch-mode extraction of ICD codes as other studies have described. Espino found that ICD codes for diagnoses (assigned by ED physicians) arrived at the RODS system on average 7.5 hours after ICD codes for chief complaints (assigned by ED registration clerks). The maximum time delay was 80.6 hours. Because the ICD codes for chief complaints and diagnoses were transmitted in real time, this measurement of time latency includes only a negligible transmission delay. Thus, nearly all of the 7.5 hours comprises patient waiting time, time for the physician to see the patient, and time for the physician to assign ICD codes to the visit using a point-of-care system.
In summary, a pervasive methodological limitation of reported studies is failure to measure and report the distribution of time latencies between patient presentation to the healthcare system and appearance of an ICD code in data systems.The single study that measured time latency was conducted in a best case—and non representative—situation. In the absence of definitive studies, our best assessment of time latencies and availability—based on the literature and our knowledge of biosurveillance systems and the healthcare system—is summarized in Table 23.12.
This someone may or may not be the person who originally elicited the information from the patient. For example, a triage nurse may elicit the chief complaint and write it on paper, and then the registration clerk, using the chief complaint on paper, enters an ICD code into a computer.
Point in Process
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