The topics below are the most common issues that we identify when validating apps to run on our platform. We suggest you work through each of these before submitting an app for validation.
- Avoid Multiple Resource Calls
- Implement Paging
- Posting Documents Using DocumentReference Resource
- Requests by Specific LOINC Codes
- Leverage Query Parameters
- Review Filtering Options
- Using Appropriate Scopes for SMART Launch
- Registering More Scopes than App Uses
- Authorization Durations Longer than 10 Minutes
- Cerner Client Deployment
Avoid Multiple Resource Calls
Ensure that your app is efficient in the way it makes API calls. Duplicate API calls should be removed to avoid additional performance load on the system and improve application load time. As part of the technical review process, we will review logs to see if calls are identical each time and if they are retrieving the same data set.
Your app should handle paging for all resources, even if our server does not support it yet. This ensures your app is compatible with more implementations (including future versions of our server if we add paging to improve performance of resources that do not currently page).
Queries on some resources can result in large data sets. If you do not implement paging logic, the application can miss relevant information because the system will not load more than just the initial page. This creates potential for the system to not account for the entire patient dataset.
In addition, if your application is showing results directly to the user, it probably does not want to show hundreds of records at a time to a user. It’s also possible your application may not have the memory available to hold all data at one time. These are all factors that you should consider when determining a page size that is right for your application.
There are two ways we recommend that you test
your logic once implemented. First, you can set page size to a lower
value using the
_count parameter in the API calls. Another way is to
make calls for a patient with a lot of data in the Sandbox domain. You can read
about our available sandbox test patients
to find a patient who has sufficient data for paging.
Posting Documents Using DocumentReference Resource
If your app uses the DocumentReference resource to post clinical notes back to the system, the following provides some additional parameters to follow to ensure that your document is displayed as intended.
Document Type: We accept HTML5 conventions and only XHTML
formatted documents are supported. Our system converts them to RTF
because that is the current requirement for posting to the Cerner EMR.
Since documents are being converted from one format type to another,
there is potential for loss of fidelity.
- A common error we have seen is with the use of
<br>tags. In XHTML, they need to be self-closed as follows:
<br />. This greatly enhances the accuracy our internal conversion tools.
- Some sanitization is run on provided XHMTL. For example:
styletags will be removed completely. Other tags (
textarea) may be removed but the text within will remain.
- Table styling is not fully supported
- A common error we have seen is with the use of
Modifier Elements: implicitRules, and modifierExtension are not supported and will be rejected if present. In addition, each resource will call out modifier elements that are not supported. For example: DocumentReference create calls out all unsupported modifiers within the implementation notes section.
Special Formatting: Please do not use specialized formatting
document. It is also not recommended that you support multiple
languages within your documents, as this has proven to be error prone
with our current conversion tools.
- If special formatting is needed, we recommend that you post your formatted text as image files within the HTML.
Images: If posting images within your documents or as the documents themselves, external image links will not function as intended. All images must be embedded Base64 encoded files using web-safe image formats due to file size. Examples are as follows:
<img alt="image" src='data:image/png;base64, <-ENCODED IMAGE-> ' />
- Testing: There are several XHTML validators that can be used to test your document. We suggest using XHTML 1.0 strict as the document type to run your validation with. Try using:
Requests by Specific LOINC Codes
Cerner maps proprietary codes to standard terminologies as part of our implementation process. For example, LOINC codes are exposed within some resources. In some cases, these mappings do not cover all the possible variances in the ways hospitals have implemented their EHRs. When EHRs were originally implemented, it was common to use proprietary codes to document labs and measurements that don’t map directly to the LOINC codes defined by the FHIR specification.
For the Observation resource, we have seen apps developed that use a set of LOINC codes as a filter to get specific results. If your app uses specific codes to query for data, you should determine if the request should be broader and include more possible codes to account for different ways data might be coded or work with us to determine the best way to return the information you need.
For example, lead can be performed on blood, capillary blood, or venous blood.
Hospital A uses a proprietary code for lead which maps to LOINC code
(Lead [Mass/volume] in Blood)
Hospital B uses a proprietary code for lead which maps to LOINC code
(Lead [Mass/volume] in Venous blood)
If you are using a specific code to query for lead and use code
5671-3, then your app would only return results when installed at
Hospital A. Your app would return nothing if installed at
Hospital B. You need to ensure that all codes are accounted for in
order for the app to work at all sites.
Another scenario is where hospitals have different tests and codes setup for different methodologies. An example is when a separate test and code is created to document blood lead collected by venipuncture versus a capillary draw, which is a common collection method for children. On occasion, client proprietary codes may not map directly to any LOINC code. For special cases where we discover a proprietary code that does not map cleanly to any standard, we will work with you to figure out the best option for that mapping during deployment.
For each of these scenarios, it is one thing to validate against our sandbox to adhere to the FHIR specification, but we also need to validate your app at each client site to ensure that there aren’t any hospital-specific considerations to be aware of. We will do this when we connect your app to a hospital domain. We will work with you to resolve any of these hospital-specific considerations.
The above examples use lead, but similar considerations could exist for virtually any lab or measurement where concept mapping and specific LOINC codes are used. If your app uses specific LOINC codes to query for information, contact us and we will help you work through any considerations that might exist.
Leverage Query Parameters
We have seen a lot of instances of developers performing post-query filtering rather than leveraging the query parameters defined by the API. We recommend using the available query parameters, such as this example for the Patient resource. Query parameters make the dataset more predictable, speed up your searches, and are more reliable than relying on post-query filtering.
Review Filtering Options
Using query parameters is recommended over post-query filtering (when possible). Regardless of the method used to filter results, ensure that your application handles resources that have been marked in error or invalid using the appropriate status field(s) for each resource.
You should review your app’s status filtering logic to ensure that the appropriate results are displayed. For Cerner’s implementation of the HL7 FHIR® standard (based on DSTU 2 Final (1.0.2)), it is particularly recommended for the MedicationOrder or Observation resources. It would be a patient safety issue if an uncharted value was displayed to a user. Please double-check the status codes you use from the MedicationOrderStatus or ObservationStatus value sets.
Typically, for MedicationOrder, only medications in
Completed statuses are displayed. For Observation, only results in
Amended statuses are displayed.
You can read about our available sandbox test patients to find a patient that has some entered-in-error results to test with.
The Condition, MedicationStatement, and Observation resources do not support filtering by the encounter parameter in the current implantation of Ignite APIs for Millennium. If you do use these resources, your app may need to implement a post-filter to display only the current encounter.
Using Appropriate Scopes for SMART Launch
SMART on FHIR defines OAuth2 access scopes that correspond directly to FHIR resource types. We define read and write permissions for patient-specific and user-level access. Patient-specific scopes allow access to specific data about a single patient. User-level scopes allow access to specific data that a user can access.
We have seen some situations where it is appropriate to use user-level scopes, but in most cases with a patient in context, you should be using patient-centric scopes.
Registering More Scopes than App Uses
Ensure you are only requesting scopes that are used. We will ask you to remove unused scopes from registration if you do not use those resources or actions.
Authorization Durations Longer than 10 Minutes
The default duration of access received through the authorization grant workflow is a single token that is valid for 570 seconds (~10 minutes). For apps that need access to services for longer durations, some apps we have validated request a new token each time, but there is a more streamlined method available.
By requesting the
online_access scope, the system grants a
that can be used for duration of a user’s authenticated session.
Such refresh tokens are valid until either the user explicitly logs out,
the session is terminated by an administrator, or other risk mechanisms
(timeouts, etc.) require a user to be re-authenticated.
Cerner Client Deployment
Using Video in Your App
Most Cerner clients deploy Cerner Millennium user apps as a Citrix XenApp® session connected from a shared server-based computing environment. If your app uses videos, we have found this can challenge the Citrix connection because only so much bandwidth can be assigned to each Citrix connection.
We determined that the preferred method for your app to play video is to open
a new window using a custom code and load the web page containing video.
This way the video opens using the hospital’s network and the Citrix connection is not affected.
Also, when the app is deployed, the hospital’s IT staff need to ensure that:
- The device running the video has the correct video codec installed
- A proper speaker or headset is connected for sound
For this routine to work, the following META tag must be included in the
HEAD of the HTML file:
<META content='APPLINK' name='discern'>
The following example illustrates opening a web page through a shell execute. When Citrix is configured for server-to-client redirection and the link is clicked, your local default web browser opens and is directed to the link provided.
Single Patient and Multi-Patient Views
Cerner’s EMR, PowerChart, has two main views that can be used to view patient information: Patient Chart view and Organizer view. It is critical that you distinguish which of these views works best for the functionality of your app and design your app accordingly.
The MPages worklist framework allows hospitals to use multi-patient and multi-item views at the organizer level of PowerChart. These views assist clinicians in organizing and prioritizing their work by providing key information about a population of patients or items and in some cases, allowing quick access to patients’ medical records, improving their efficiency and productivity. The most common worklist layout type currently available is the Patient Organizer View which supports the display of multiple patients along with key information about the status and care of those patients.
Patient Chart View
The Patient Chart view in PowerChart displays information for a single patient. It is accessed by selecting a patient from one of the Organizer views or from Patient Search. Multiple patient charts can be open at the same time, and you can easily move between open charts by clicking the patient’s name in the Patient Context toolbar. The Patient Chart view is made up of two panes - the Table of Contents and the Workspace. The Table of Contents is displayed on the left side of the window and allows you to quickly navigate to any area of the patient’s chart. Clicking a PowerChart component in the Table of Contents, such as a SMART app, opens that component’s Workspace view. The Workspace view displays and changes based on which PowerChart component is selected from the Table of Contents. Each view can include multiple windows, that are accessed by clicking tabs or buttons in that view. If you open your SMART app from the Table of Contents, information for the patient is displayed in the Workspace view.
If your app is best used for managing a population of patients, then it should be optimized to be used at the Organizer view level. If your app is best used in the context of a single patient, it is critical that the user should not be able to access Organizer level information, such as patient lists or other patient’s data. This could be hazardous in the context of the single-patient Patient Chart view because users could become confused as to which patient’s information they are viewing. This is especially critical if you are porting your app to be used within the SMART on FHIR framework. We have seen a few examples where developers didn’t remove functionality such as patient search and we had to have them restart their validation process once that functionality was removed.
Session Bleed Issue
When you are running a SMART app in multiple open charts in PowerChart, there is potential that the app instance will share patient context and show same patient’s data on two separate charts. In order to avoid this, please read our SMART topic on sessionStorage. If your application uses the open sourcce fhir-client.js library, please read the secion on minimum required version and additional code that must be added in order to fix a session bleed issue.
Note: This cannot be properly tested until you are beginning validation and we are running your app directly in PowerChart. The following recreation steps are for your information once you have access to PowerChart.
To recreate the issue:
- Open the chart for Patient A and launch an app.
- Go back to the Patient List and open an additional chart (Patient B), then launch an app for that patient.
- On Patient A’s chart, click As Of in the upper right corner to refresh the content of PowerChart. If the application displays the information for Patient B within the chart for Patient A, then you need to implement the change mentioned above.
During application validation, we do a security review. We’ve gathered some common topics that are covered which should help you think through the security of your application. There are also examples of tools that can guide secure development of your application.
An automated security analysis of the app must be completed prior to the security review. There are many tools available for this including paid and free offerings. If available, producing a report from tools such as HP Fortify, IBM AppScan and Veracode are preferred.
The reports should produce results that are free of critical and high results. In the event that medium results are found, the submitter will be asked for a mitigation plan and timelines to resolve the found vulnerabilities.
It is required that you test your app’s SSL/TLS status against SSLLabs during a security review. The app must at least score an A on SSLLabs to pass the security review. To assist in reaching this score, the items below should be taken into consideration:
- Disable all SSL versions
- Disable TLS version 1.0
- Review the list of cipher suites and remove any insecure cipher suites
- Ensure that the handshake simulation user agents that are relevant to the app are functional
- Enable forward secrecy, if practical
- Ensure that TLS_FALLBACK_SCSV is enabled
Data Flow Diagram
Ensure that the data flow diagram displays the flow of data, including PHI (protected health information), during the course of normal usage. The data flow diagram should also display the authentication and authorization decisions that are being made.
The threat model should make use of a tool like Microsoft Threat Model 2016 or similar. The threat model must show the assets that the app uses during runtime as well as the other apps and systems that it connects to or accepts connections from.
The threat model must also include the following:
- Authentication interactions with external sources (for example, the Cerner OAuth service)
- Information related to the hosting environment that the app is hosted in (for example, AWS, Azure, third-party, or a self-run data center)
- Define the trust boundaries crossed during runtime
If using the MS Threat Model 2016 tool, the found threats must be responded to in the Analysis view.
Third-Party Tools and Libraries
The use of a tool like OWASP’s Dependency Check greatly reduces the exposure to malicious dependencies prior to deploying your app. Dependency Check is a utility that identifies project dependencies and checks if there are any known, publicly disclosed, vulnerabilities.
We recommend that you use this tool to reveal any issues with the libraries that are used by the app and assist with the manual review of the list of third party libraries that are requested during a security review. If using Dependency Check, you should submit a report during security review.
The patching policy must include how the app owner plans to patch its software in the event that a critical vulnerability is discovered. The patching policy must include timeframes for when a vulnerability will be patched (for example, within 48 hours of knowledge of a critical vulnerability, within seven days of a high vulnerability, and so on).