Circannual variation in glycohemoglobin in Singapore.
BACKGROUND
Glycohemoglobin is routinely used for the monitoring of glycemic control in patients with diabetes mellitus. The yearly pattern of glycohemoglobin was examined in a tropical country to assess the effect of festivities without the confounding effect of seasonal variation in temperature and climate.


METHODS
Details of all outpatient HbA1c measurements with identified ethnicity over 3 y were examined with respect to date of sampling and compared to the dates of public holidays.


RESULTS
There were 40267 records available. There was a circannual pattern with a peak in February/March, a minor peak in July/August and a nadir in November/December with an amplitude of 0.5%. Date of sampling was a significant factor in predicting HbA1c>8.0% despite controlling for race, sex and age. Odds ratios (vs. Quarter 4) were: Quarter 1 1.34 (1.26-1.43); Quarter 2 1.10 (1.03-1.17); Quarter 3 1.11 (1.04-1.19). There was a positive correlation between the number of festive days in the preceding 3 months and the monthly mean HbA1c value. Malay and Indian patients had significantly higher HbA1c values than Chinese.


CONCLUSIONS
There is a circannual pattern of HbA1c values in adult outpatients in Singapore, reflecting the celebration of holidays in the preceding 3 months. Clinicians seeking to improve glycemic control should remember the effect of festive occasions.
Department of Laboratory Medicine, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, 308433, Singapore. Robert_Hawkins@ttsh.com.sg
Robert C
RC
Hawkins
D002940:Circadian Rhythm; D015986:Confounding Factors, Epidemiologic; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D015999:Multivariate Analysis; D012621:Seasons; D012846:Singapore; D014329:Tropical Climate
D006442:Glycated Hemoglobin