The meaning of “mean plasma glucose (MPG)” is unambiguous, but I’m having an incredibly difficult time making sense of the way the term “mean blood glucose (MBG)” is used in medical research literature on diabetes. It’s not clear whether it denotes mean plasma glucose as well, or whole blood glucose, or whether the term is used inconsistently in the literature.
I have seen several sources that assert that MBG is different from MPG and refers to whole blood glucose, and relate the two with the equation MPG = MBG * 1.11. However, none of the sources I’ve found that specifically distinguish between MBG and MPG are formal articles in medical journals.
In the professional literature, the term MBG is never clarified -- I haven’t been able to find even one paper that specifically defines it as either whole blood or plasma glucose -- and it seems to be used in inconsistent and contradictory ways between different articles. Some articles use the term MPG exclusively, and at no point distinguish it from MBG. Others use MBG exclusively, and neither distinguish it from MPG nor specify whether it refers to plasma or whole blood.
Still others alternate between the terms.
- In some of those cases, context clearly implies that they have different meanings.
- In other cases it’s unclear from context whether the terms are being used interchangeably (implying that MBG refers to plasma glucose), or whether two terms are used because they mean different things.
- In still other cases, the term MBG is used in reference to the same things for which other articles use the term MPG, implying that the terms are interchangeable. For example, I’ve seen both the DCCT and ADAG conversion equations stated in terms of both MBG and MPG, but the numbers are always the same, and I’ve seen articles use the term MBG in reference to articles that only used the term MPG.
- In no case, however, is it explicitly made clear whether and how MBG differs from MPG
I’ve provided examples of all of the above at the end, with links.
The ADAG study further adds to the confusion. The article never mentions either MBG or MPG, instead introducing the term “average glucose” (AG), without indicating whether it’s a synonym for MPG and/or MBG or whether there’s some distinction in meaning from either or both of those terms, nor whether it denotes whole blood or plasma glucose. I’ve gathered from numerous references to the ADAG study that AG is in fact plasma glucose, and that the ubiquitous regression equation produced by that study relates HbA1c to MPG (which further implies that articles that use MBG in the ADAG equation are treating it as synonymous with MPG). However, the article never actually specifies that the “average glucose” it talks about is plasma glucose, apparently assuming that this is self-evident to professionals, and sheds no light on the MBG/MPG distinction, if any, nor on why a different term is used in this article than in all other literature on the same subject. I haven’t seen the term AG used in any other article, except sometimes when citing the ADAG study.
I have had no luck in finding any information that clarifies how these terms are used. Can anyone shed some light on this so that I can be sure I understand the literature correctly?
- Are MBG and MPG interchangeable, both referring to mean plasma glucose? If so, why do some articles use both, in a way that creates the impression that they have different meanings?
- Does MBG mean something different? If so, what exactly does it mean, whole blood glucose, or something else? Why is the term sometimes used in articles discussing the relationship between blood glucose and HbA1c, given that research establishing that relationship (DCCT, ADAG, and the more recent GMI study) always quantifies it in terms of mean plasma glucose?
- In either case, why does the ADAG study use a different term altogether? Is AG synonymous with MPG, or is there a distinction?
- When the term MBG appears in articles, is it a safe assumption that any associated numbers are either plasma or plasma equivalent values?
- In writing about this topic, is MBG the preferred (or at least acceptable) term to refer to averages based on values obtained by meters that report plasma equivalents and CGMs calibrated with such meters, or would that be considered ambiguous, and is the term MPG preferred?
Examples:
The following resources specifically define MBG as whole blood glucose and provide the equation MPG = MBG x 1.11:
- http://www.diabetesincontrol.com/issue-93-item-7-why-relating-a1c-ghb-to-mean-blood-glucose-mbg-is-important/
- http://www.chirus.com/download_files/a1cnow+_90704_rev_a.pdf
- http://www.privatemdlabs.com/lab_tests.php?view=search_results&show=1578&category=12&search=CEA (this one also specifically says that eAG is MPG)
- These articles only use MPG in discussing the relationship of mean glucose and HbA1c:
- This article only uses MBG in discussing the same topic: “Glycated Hemoglobin (HbA1c): Clinical Applications of a Mathematical Concept” Acta Inform Med. 2016 Jul 16
- This article uses the term MBG a single time (in the CONCLUSIONS section of the abstract), but otherwise uses only the term MPG, including in the same section where MBG appears. The context provides no clues as to why a different term is used in that one instance and whether it has a different meaning. Kuenen JC, Borg R, et al., “Does Glucose Variability Influence the Relationship Between Mean Plasma Glucose and HbA1c Levels in Type 1 and Type 2 Diabetic Patients?” Diabetes Care 2011
- This article alternates between the terms, sometimes in a single sentence, in a way that clearly implies that they have different meanings, but it never explains how the terms differ: Konstantinos K, Loukia S “Is There a Relationship between Mean Blood Glucose and Glycated Hemoglobin?” J Diabetes Sci Technol. 2011. Inexplicably, however, Table 2, which lists regression formulas from various studies, uses MBG in all formulas, regardless of which term was used in the original study. So, the same article treats the two terms as different, but then treats MBG as equivalent to MPG in reference to other studies!
- Judith Kuenen’s thesis, “Measures of glycemic control: do we need more than HbA1c?”, seems to imply that the terms are interchangeable. In chapter 3, she reproduces the Diabetes Care 2011 study above that uses MPG throughout and a single instance of MBG. Chapters 4 and 5 consist of two of her own studies, in which she only uses the term MPG. However, in her “General Discussion” in chapter 9, she exclusively uses the term MBG in discussing the subject, even when referring to the studies in chapters 4 and 5 that only talk about MPG.
- The Rohlfing 2002 article cited above states the DCCT formula with MPG. The literature in general makes it clear that the DCCT regression formula describes the relationship between HbA1c and plasma glucose.
- However, this article states the DCCT regression formula with MBG: “Glycated Hemoglobin (HbA1c): Clinical Applications of a Mathematical Concept”
- This resource also states the DCCT formula in terms of MBG: https://diabetestalk.net/diabetes/hgb-a1c-with-mbg-estimation
- This one states the ADAG regression formula with the term eAG, but specifies that it’s the relationship between HbA1c and MBG: “Clinically Significant Disagreement between Mean Blood Glucose and Estimated Average Glucose in Two Populations: Implications for Diabetes Management” J Diabetes Sci Technol. 2009 Sep
- Countless references and resources say the ADAG formula relates MPG and HbA1c. Usually the term “eAG” is used in the formula itself, but it’s specified that formula is for the MPG-HbA1c relationship. Several explicitly say MPG in the formula: https://miniwebtool.com/hba1c-calculator/ http://jteamblogs.blogspot.com/2013/08/diabetes.html
- As mentioned above, Table 2 in “Is There a Relationship between Mean Blood Glucose and Glycated Hemoglobin?” states all the regression formulas with MBG, including the DCCT and ADAG formulas, which describe the relationship between HbA1c and mean plasma glucose
