EHR to HL7 FHIR Integration: The Software Developer’s Guide – Part 3

Software Engineering | Matjaz Bravc |
24 August 2021

Welcome to the final post of this blog series where I show you how to create simple custom EHR to HL7 FHIR* integration using the latest Microsoft tech stack. In the first article, I introduced the HL7 FHIR standard and the .NET 5 framework. In the second post, I shared how you can integrate Patients into your solution. In this third part, I will describe how to integrate Patient Observations (blood tests).

HL7 FHIR OBSERVATIONS

As the HL7 documentation describes, Observations are a central element in healthcare, used to support diagnosis, monitor progress, determine baselines and patterns, and even capture demographic characteristics. Most observations are simple name/value pair assertions with some metadata, but some observations group other observations together logically or can even be multi-component observations. The DiagnosticReport resource provides a clinical or workflow context for a set of observations. The Observation resource is referenced by DiagnosticReport to represent laboratory, imaging, and other clinical and diagnostic data to form a complete report.

Uses for the Observation resource include:

Vital signs such as body weight, blood pressure, and temperature
Laboratory data like blood glucose or an estimated GFR
Imaging results like bone density or foetal measurements
Clinical findings such as abdominal tenderness
Device measurements such as EKG data or pulse oximetry data
Clinical assessment tools such as APGAR or a Glasgow Coma Score
Personal characteristics such as eye colour
Social history like tobacco use, family support, or cognitive status
Core characteristics like pregnancy status or a death assertion

But first, some explanation...

CBC TESTS

This demo focuses on several blood observations which are part of a complete blood count (CBC). CBC is a group of tests that evaluate the cells that circulate in the blood, including red blood cells (RBCs, or erythrocytes), white blood cells (WBCs, or leukocytes), and platelets (PLTs, or thrombocytes). The CBC can evaluate your overall health and detect a variety of diseases and conditions, such as infections, anaemia, and leukaemia. Blood cells are produced and mature primarily in the bone marrow and, under normal circumstances, are released into the bloodstream as needed.

A CBC is typically performed using an automated instrument that measures various parameters, including cell count and the physical features of some of the cells. A standard CBC includes:

Red blood cell tests:

• Red blood cell count – the actual number of red blood cells in your blood sample.
• Haemoglobin – the total amount of the oxygen-carrying protein in the blood, which generally reflects the number of red blood cells in the blood.
• Haematocrit – the percentage of your total blood volume that consists of red blood cells.

White blood cell tests:

• White blood cell count – the total number of white blood cells in your blood sample.
• White blood cell differential – may be included as part of the CBC or may be done in follow-up if the WBC count is high or low.

For Observations, like the results of such CBC tests, there are several endpoints available. Using Swagger UI “allows anyone – be it your development team or your end consumers – to visualize and interact with the API’s resources without having any of the implementation logic in place. It’s automatically generated from your OpenAPI Specification, with the visual documentation making it easy for back end implementation and client side consumption.”