title: [One-year variability of HbA1c in children and adolescents with type 1 diabetes - preliminary results].
abstract: BACKGROUND
  The glycated A1c hemoglobin (HbA(1)c) is an accepted marker of glycemic control in patients with type 1 diabetes (T1DM) and a predictor of long-term microvascular diabetic complications. There have been reports of seasonal fluctuations of HbA(1)c levels in type 1 and type 2 diabetic patients of different age.
  
  
  OBJECTIVE
  The aim of the study was to investigate retrospectively investigate seasonal variations of HbA(1)c levels in a pediatric population of T1DM patients over a one-year period.
  
  
  METHODS
  The study group included 473 patients aged 2.4 -18 years (mean 13.3 ± 3.7) with T1DM duration of at least 6 months in whom HbA(1) c levels were tested between November 1, 2008 and October 31, 2009. HbA(1)c was measured by high performance liquid chromatography (HPLC).
  
  
  RESULTS
  The total number of 1417 HbA(1)c tests were performed (mean 3.0 tests/patient/year). Mean HbA(1)c level was (mean ± SD) 7.7 ± 1.5% (range 5.2 -15.7%; median 7.4%; 25-75% range: 6.7 -8.2%). Statistically significant differences in monthly HbA(1)c levels were found (analysis of variance; p < 0.001). The lowest HbA(1)c levels, observed in August and September, were significantly lower than in February, March, April and December. Relative HbA(1)c levels, expressed as percentages of individual patient's mean value for twelve months, showed similar seasonal fluctuations: the lowest values were observed in August and September and the highest were noted in February, March, April, November and December.
  
  
  CONCLUSIONS
  1. HbA(1)c levels in young T1DM patients show seasonal variability. 2. Considering seasonal HbA(1)c fluctuations in patients education and management schedules could improve glycemic control. 3. Seasonal changes of HbA(1)c levels should be considered in short-term(lasting several months) clinical study designs.
authors.affiliation: Klinika Pediatrii, Katedry Pediatrii Uniwersytetu Medycznego w Lodzi. beata.mianowska@umed.lodz.pl
authors.forename: Beata
authors.initials: B
authors.lastname: Mianowska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Fendler
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Szadkowska
authors.forename: Iwona
authors.initials: I
authors.lastname: Pietrzak
authors.forename: Anna
authors.initials: A
authors.lastname: Baranowska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Młynarski
mesh_terms: D000293:Adolescent; D001786:Blood Glucose / Q000032:analysis*; D002648:Child; D002675:Child, Preschool; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism*; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D008297:Male; D010507:Periodicity; D011044:Poland; D012016:Reference Values; D012621:Seasons
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin; C517652:hemoglobin A1c protein, human