HbA1c LOINC 59261-8 (IFCC-RMP method but % units)

General
1

I have a question about the HbA1c LOINC code 59261-8 – “Hemoglobin A1c/Hemoglobin.total standardized per IFCC-RMP for CDT in Blood”.

On the LOINC details page, I see:

  • Component: Hemoglobin A1c/Hemoglobin.total^^standardized per IFCC-RMP for CDT

  • System: Blood

  • Property: SFr

  • Scale: Qn

  • Example UCUM Units: %

My understanding is that IFCC standardization for HbA1c is normally reported in mmol/mol, whereas the NGSP approach reports results in percent (%). Because this LOINC name explicitly references IFCC-RMP, but the example units are “%”, I am unsure how laboratories and implementers are expected to use this code.

I would really appreciate clarification on the following points:

  1. Was 59261-8 intended for HbA1c results reported in % despite mentioning IFCC-RMP, or is it meant for IFCC-style reporting?

  2. Is there (or will there be) a separate LOINC code for HbA1c measured according to IFCC-RMP and reported in mmol/mol?

  3. Does the “Example UCUM Units” field for this code reflect current LOINC guidance, or is an update being considered?

  4. Any practical implementation advice for labs that use IFCC methods but need to support both NGSP (%) and IFCC (mmol/mol) reporting?

I’m asking because this combination of IFCC-RMP in the name and “%” as the example unit can create confusion in mappings and in clinical systems that rely on LOINC + UCUM for validation.

Thanks in advance for any clarification or shared experience.

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2

Hello Rita! I apologize for missing this question this past winter. I will try to answer a portion of the questions. The unit of measure % “percent” actually covers a lot of areas, such as 1 type of cell amongst other cells, or some portion of grams against a gram (Mass Fraction). When I see example units of % with a property of SFr (Substance Fraction), I know that this is already molar based, such as mmol/mol. I would expect the EXAMPLE UCUM units to just be examples. I will run this past the Lab LOINC committee and see if there’s been a miscommunication in the Example units of measure. Please note on the details page of 59261-8 that this term was not expected to be used in the United States. “This term is not proposed for use in the United States, who will continue to use the NGSP protocol and report the Hgb A1c as %.” I will get back with you.

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