Thursday, November 16, 2017

CDISC-CT madness: a solution

In my previous post, I reported about the ongoing madness in the development of new CDISC controlled terminology (CT) for laboratory tests, microbiology and a few others, where CDISC developed its own CT whereas much better systems (not lists) already exists.

Yesterday, I found another jewel of where this madness leads to. It is about the development of the "Ebola Therapeutic Area User Guide", and how the observations "highest temperature in the last 24 hours", "highest pulse in the last 24 hours" and "lowest blood pressure in the last 24 hours" should be represented as SDTM. Here is a small part of the very long discussion from the CDISC wiki:

In the SDTM Vital Signs dataset, systolic and diastolic blood pressure must be defined by VSTESTCD=SYSBP and VSTESTCD=DIABP. So, in the CT phylosophy, "highest value in 24 hours" must be added through an additional variable. But which one? We have other such variables, such as VSPOS (position),VSLOC (location), and VSLAT (laterality), but there is none such for expressing the "maximum value".
In the post on the SDTM wiki, it is suggested that VSTSDTL (Vital Signs Examination Detail) be added and used. The contents of it would essentially be free text which is not so well understandable by machines.

However, there is a very simple solution!

"Maximum in the period of 24 hours" is defined by LOINC. So I was not surprised that I could find exact LOINC codes for the four cases mentioned. A simple search (<5 minutes) in the LOINC database, led to following results:

  • Highest temperature in 24 hours:
    LOINC Code: 8315-4
    LOINC (short) Name: Body temperature:Temp:24H^max:XXX:Qn
    LOINC Long (common) Name: Body temperature 24 hour maximum

  • Highest pulse/heart rate in 24 hours:
    LOINC Code: 
    8873-2LOINC (short) Name: Heart rate:NRat:24H^max:XXX:QnLOINC Long (common) Name: Heart rate 24 hour maximum

  • Lowest diastolic blood pressure in 24 hours:
    LOINC Code:
    8477-2LOINC (short) Name: Intravascular diastolic:Pres:24H^min:XXX:Qn
    LOINC Long (common) Name:
    Diastolic blood pressure 24 hour minimum
  • Lowest systolic blood pressure in 24 hours:
    LOINC Code: 8495-4LOINC (short) Name: Intravascular systolic:Pres:24H^min:XXX:Qn
    LOINC Long (common) Name: Systolic blood pressure 24 hour minimum
"Voila!" - problem solved! While the SDTM people are discussing for hours, we could solve the problem in 5 minutes by just using a much better coding system than the CDISC-CT system.
All we then need to do is to add these LOINC codes in VSLOINC, and we are ready. If it were not mandated by the SDTM-IG, we could even leave VSTESTCD and VSTEST out, as the value of VSLOINC containing the LOINC code has the full and 100% correct and exact description of the test that was performed. The details of what the code means can be easily retrieved by any modern tool by e.g. using RESTful web services.

 It is really time that the SDTM and CDISC-CT teams start rethinking a few things...

===== Addition =====

As a little "encore", here how you can easily find out using our RESTful web services:

What you see is a snapshot of an application developed by one my (bright) students, Ms. Eva Winter (as part of her Bachelor thesis), allowing to do a dynamic search: each time a character is entered (or after each word, by entering a space or "Enter"), the RESTful web service is called, and the list (ordered by relevance) of proposed LOINC codes is updated. The selected LOINC information can then be saved as XML or as JSON.

===== Addition 2 =====

You can of course also use the excellent LOINC RESTful web services developed by the US NLM (National Library of Medicine). For example, in order to get the 10 most relevant LOINC codes for the search term "systolic blood pressure maximum", use the request "", and you will obtain similar results in JSON format.

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