Oral Presentation Australasian Diabetes in Pregnancy Society Annual Scientific Meeting 2016

Is there a seasonal variation in Hba1c? (#4)

Hui Yi Ng 1 , Rowena Hockings 2 , Garry Morris 3 , Fernando San Gil 4 , Robert Moses 1
  1. Endocrinology, Wollongong Hospital, Wollongong, NSW, Australia
  2. Research Central, Wollongong Hospital, Wollongong, NSW, Australia
  3. Southern IML Pathology, Wollongong, NSW, Australia
  4. SEALS pathology, Wollongong, NSW, Australia

Objective

The glucose tolerance test (GTT) is still the preferred and recommended test for gestational diabetes mellitus (GDM).1 However, the prevalence of GDM has a significant seasonal variation. In a temperate climate and with a nationally representative population, the prevalence of GDM is 29% higher in summer and 27% lower in winter compared with the median.2 The HbA1c has been proposed as an alternate diagnostic method.3 However, numerous reports indicate that in the northern hemisphere the HbA1c is higher in winter.4-6 The aim of this study was to assess if there was a seasonal variation in the HbA1c in the southern hemisphere and in a temperate climate.

Methods

Southern IML Pathology (SIML) is the major provider of pathology services in Wollongong and surrounding areas. De-identified HbA1c data were obtained for 5 years from SIML (January 2011 to December 2015). The data included the date of collection, date of birth, gender and HbA1c result.

Results

A total of 203,170 HbA1c results was available for analysis. These results were from all people with diabetes. The median HbA1c for each season was 6.6% (48 mmol/mol). The median HbA1c (IQR) for summer was 6.6% (48 mmol/mol) (1.6), autumn 6.6% (48 mmol/mol) (1.6), winter 6.6% (48 mmol/mol) (1.8) and spring 6.6% (48 mmol/mol) (1.7). While these differences were deemed statistically significant (due to the large numbers used for analysis), it was felt unlikely to be of clinical significance.

Conclusions

Whereas in the northern hemisphere the HbA1c does exhibit seasonal variation4-6, this was most likely due to reduced exercise and the coincidence of the festive seasons with winter. No clinically significant differences were apparent in a temperate climate. Specific data are required for pregnancy. HbA1c could be considered as an alternative diagnostic test during pregnancy to potentially overcome the changes in prevalence with seasons with GTT.

  1. American Diabetes Association. Gestational Diabetes Mellitus. Diabetes Care 2003 Jan; 26(suppl 1): s103-s105
  2. Moses RG, Wong VCK, Lambert K, Morris GJ, San Gil F. Seasonal changes in the prevalence of gestational diabetes mellitus. Diabetes Care May 2016.
  3. Hughes RCE, Rowan J, Florkowski CM. Is there a Role for Hba1c in Pregnancy? Curr Diab Rep (2016) 16:5.
  4. Gikas A, Siotiropoulos A, Pastromas V, Papazafiropoulou A, Apostolou O, Pappas S. Seasonal variation in fasting glucose and HbA1c in patients with type 2 diabetes. Primary care diabetes 3 (2009) 111-114.
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  6. Pereira MT, Lira D, Bacelar C, Oliveria JC, de Carvalho A. Seasonal variation of haemoglobin A1c in a Portuguese adult population. Arch Endocrinol Metab. 2015;59(3)231-5.