OBJECTIVE

To characterize the association of low HbA1c values (<4.0%) with liver enzymes and steatosis.

RESEARCH DESIGN AND METHODS

Cross-sectional study of 12,533 participants without diabetes aged <20 years in the Third National Health and Nutrition Examination Survey (1988–1994). Logistic regression models were adjusted for demographic, lifestyle, and health status variables.

RESULTS

HbA1c values ranged from 3.2 to 15.7%, and 84 participants had HbA1c <4.0% in the population (mean age 44, 52% female, 15% black or Hispanic). We observed J-shaped associations between HbA1c and liver enzymes and hepatic steatosis. In adjusted models, HbA1c <4.0% was strongly associated with elevated alanine aminotransferase (OR 3.62 [95% CI 1.09–12.02]) and aspartate aminotransferase (6.80 [2.99–15.43]).

CONCLUSIONS

Low HbA1c values were associated with liver enzymes and steatosis in the U.S. population. Liver disease may partially explain the association of HbA1c with mortality and other long-term outcomes.

Recent studies show that low HbA1c in nondiabetic individuals is associated with increased mortality (13). The biologic processes underlying this association remain unclear, although liver disease has been hypothesized (2,4). Our objective was to examine the association between low HbA1c (<4.0%); elevated liver enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST), and γ-glutamyltransferase (GGT); and hepatic steatosis in U.S. adults.

The Third National Health and Nutrition Examination Survey (NHANES III 1988–1994) was a cross-sectional survey of the U.S. population (5) and is described in detail elsewhere (6,7). We restricted our analyses to 12,533 participants without self-reported diabetes who had complete information on variables of interest.

HbA1c was measured via high-performance liquid chromatography (interassay coefficient of variation <2.0%), and values <4.0% or >11.0% were repeated for verification (7). If hemoglobin variants were present, affinity chromatography was used (7). We considered ALT, AST, and GGT elevated if they were above the laboratory-defined upper limit of normal: ALT, >40 units/L for men, >31 units/L for women; AST, >37 units/L for men, >31 units/L for women; and GGT, >51 units/L for men, >33 units/L for women (7). Hepatic steatosis detected by ultrasound was available for all participants aged 20 to 74 years and was defined as present or absent (8).

We used logistic regression to examine the association between HbA1c categories and elevated liver enzymes and hepatic steatosis. We repeated our analyses among participants who never consumed alcohol (n = 3,771). To assess the continuous associations, we fit restricted cubic splines (9). We conducted a sensitivity analysis excluding participants with anemia (hemoglobin <13.5 g/dL in men and <12.0 g/dL in women), presumed iron overload (serum transferrin saturation >44% and serum ferritin <10 ng/mL), or hepatitis B or C (n = 11,593, after exclusions). To compare low HbA1c to low fasting glucose, we modeled the 1st percentile versus the rest of the values for HbA1c (cutpoint, 4.0%) and fasting blood glucose (cutpoint, 73.4 mg/dL) in the morning fasting subsample (n = 8,747). All analyses accounted for the complex survey design (5).

Characteristics of the population are shown in Supplementary Table 1. HbA1c ranged from 3.2 to 15.7%. The prevalence of elevated ALT, AST, or GGT was 5.9, 5.3, and 13.8%, respectively. The prevalence of hepatic steatosis was 18.8%.

We observed J-shaped associations between HbA1c and elevated liver enzymes and hepatic steatosis (Fig. 1). The adjusted odds ratios (ORs) and 95% CIs are shown in Supplementary Table 2. In adjusted models with HbA1c 5.0–5.5% as reference group, HbA1c <4.0% was associated with elevated ALT (OR 3.62 [95% CI 1.09–12.02]) and AST (6.80 [2.99–15.43]). HbA1c <4.0% was also associated with elevated GGT and with hepatic steatosis, but these were not statistically significant. In addition, we found trends for higher total bilirubin, higher AST-to-ALT ratio, lower serum albumin, and lower platelets in individuals with HbA1c <4.0% (Supplementary Table 1).

When we restricted our analysis to participants with no history of alcohol consumption, HbA1c <4.0% was significantly associated with elevated ALT, AST, and GGT but not hepatic steatosis. After excluding participants with anemia, iron overload, and hepatitis B or C, the ORs remained elevated but were no longer statistically significant.

HbA1c below the 1st percentile was associated with elevated ALT (OR 3.18 [95% CI 1.00–10.27]) and AST (5.80 [2.55–13.19]) but not with elevated GGT or hepatic steatosis (Supplementary Table 3). Fasting glucose below the 1st percentile was not significantly associated with elevated ALT, AST, GGT, or hepatic steatosis.

We observed J-shaped associations of HbA1c with liver enzymes and hepatic steatosis in this sample of U.S. adults (8). Specifically, HbA1c values <4.0% were significantly associated with elevated ALT and AST, while associations with hepatic steatosis and elevated GGT were less pronounced. After exclusion of participants with anemia, iron overload, and hepatitis B or C, these associations were no longer significant.

New recommendations for the use of HbA1c for diagnosis of diabetes (10) will likely result in more HbA1c testing. In light of evidence that very low HbA1c values are associated with total mortality (13), it is important to understand the clinical significance of low HbA1c values. Our study extends prior work in NHANES III, which reported elevated ALT and AST and a high prevalence of hepatitis C (11.1%) in individuals with low HbA1c (2). Hypothesized mechanisms by which low HbA1c values may be associated with both abnormal liver function and increased mortality include alcohol consumption, abnormal erythrocyte turnover and function (e.g., anemia and iron overload) (11,12), the viral hepatitides (2), and abnormally low glycemia (2). We found little evidence that this association was mediated by alcohol consumption. After excluding participants with anemia, iron overload, and hepatitis B or C, the association of HbA1c values <4.0% and elevated ALT and AST were no longer significant, suggesting these factors may partially mediate the association. We did not observe an association between low fasting glucose and liver disease, suggesting that the association with low HbA1c may be independent of glycemic pathways. Low HbA1c may be a general marker of poor health, analogous to low cholesterol levels (13).

Certain limitations of this study should be considered when interpreting our results. We had one measurement of the liver enzymes, and previous studies demonstrate variability in markers (14) and ultrasound is moderately reliable for detecting hepatic steatosis compared with liver biopsy (15). Although the NHANES III study protocol included repeat HbA1c testing for extreme HbA1c values and we performed sensitivity analyses, we were not able to assess the potential influence of decreased erythrocyte life span per se (hemolysis), which may alter HbA1c (11). Strengths of this study include the large study population, rigorous data collection procedures, and nationally representative design. We examined the association of HbA1c with liver disease across the entire spectrum of HbA1c values in nondiabetic individuals, and we included a comprehensive liver disease assessment.

In conclusion, we observed J-shaped associations between HbA1c and elevated liver enzymes and hepatic steatosis by ultrasound in a representative sample of the U.S. population. Additional work is needed to determine how liver disease may be related to the observed associations of low HbA1c with total mortality.

A.L.C. was supported by National Institutes of Health (NIH)/National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) Training Grant T32-DK-062707. M.L. was supported by NIH/NIDDK Grant R01-DK-083393 and by the American Diabetes Association. J.M.C. was supported by NIH/NIDDK Grant R01-DK-083393. E.S. was supported by NIH/NIDDK grants K01-DK-076595 and R01-DK-089174.

No potential conflicts of interest relevant to this article were reported.

A.L.C. analyzed data, contributed to discussion, wrote the manuscript, and reviewed and edited the manuscript. M.L. and J.M.C. researched data, contributed to discussion, and reviewed and edited the manuscript. E.S. contributed to discussion and reviewed and edited the manuscript.

1.
Selvin
E
,
Steffes
MW
,
Zhu
H
, et al
.
Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults
.
N Engl J Med
2010
;
362
:
800
811
[PubMed]
2.
Carson
AP
,
Fox
CS
,
McGuire
DK
, et al
.
Low hemoglobin A1c and risk of all-cause mortality among US adults without diabetes
.
Circ Cardiovasc Qual Outcomes
2010
;
3
:
661
667
[PubMed]
3.
Saydah
S
,
Tao
M
,
Imperatore
G
,
Gregg
E
.
GHb level and subsequent mortality among adults in the U.S
.
Diabetes Care
2009
;
32
:
1440
1446
[PubMed]
4.
McNeely M. Case study: diabetes in a patient with cirrhosis
.
Clin Diabetes
2004
;
22
:
42
43
5.
Analytical and reporting guidelines: The Third National Health and Nutrition Examination Survey, NHANES III (1988–1994) [article online], 1996. Hyattsville, MD, National Center for Health Statistics, Centers for Disease Control and Prevention. Available from http://www.cdc.gov/nchs/data/nhanes/nhanes3/nh3gui.pdf. Accessed 7 January 2011
6.
National Center for Health Statistics. Plan and Operation of the Third National Health and Nutrition Examination Survey, 1988–1994. Washington, DC, U.S. Govt. Printing Office, 1994
7.
Laboratory procedures used for the Third National Health and Nutrition Examination Survey (NHANES III), 1988–1994 [article online], 1996. Bethesda, MD, U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Environmental Health, National Center for Health Statistics. Available from http://www.cdc.gov/nchs/data/nhanes/nhanes3/cdrom/nchs/manuals/labman.pdf. Accessed 7 January 2011
8.
Third National Health and Nutrition Examination Survey: hepatic steatosis ultrasound images assessment procedures manual [article online], 2011. Hyattsville, MD, National Center For Health Statistics, Centers for Disease Control and Prevention. Available from http://www.cdc.gov/nchs/data/nhanes/nhanes3/Hepatic_Steatosis_Ultrasound_Procedures_Manual.pdf. Accessed 7 January 2011
9.
Harrell
FE
.
Regression Modeling Strategies With Applications to Linear Models, Logistic Regression, and Survival Analysis
.
New York
,
Springer
,
2001
10.
American Diabetes Association
.
Diagnosis and classification of diabetes mellitus
.
Diabetes Care
2010
;
33
(
Suppl. 1
):
S62
S69
[PubMed]
11.
Cohen
RM
,
Franco
RS
,
Khera
PK
, et al
.
Red cell life span heterogeneity in hematologically normal people is sufficient to alter HbA1c
.
Blood
2008
;
112
:
4284
4291
[PubMed]
12.
Ford
ESCC
,
Cowie
CC
,
Li
C
,
Handelsman
Y
,
Bloomgarden
ZT
.
Iron-deficiency anemia, non-iron-deficiency anemia and HbA1c among adults in the US
.
J Diabetes
2011
;
3
:
67
73
[PubMed]
13.
Volpato
S
,
Zuliani
G
,
Guralnik
JM
,
Palmieri
E
,
Fellin
R
.
The inverse association between age and cholesterol level among older patients: the role of poor health status
.
Gerontology
2001
;
47
:
36
45
[PubMed]
14.
Lazo
M
,
Selvin
E
,
Clark
JM
.
Brief communication: clinical implications of short-term variability in liver function test results
.
Ann Intern Med
2008
;
148
:
348
352
[PubMed]
15.
Gomercić
M
,
Duvnjak
M
,
Barsić
N
.
Ultrasonography in the diagnosis of nonalcoholic fatty liver disease
.
Acta Med Croatica
2009
;
63
(
Suppl. 3
):
1
3
[PubMed]
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Supplementary data