HbA1c as a screening tool for cystic fibrosis related diabetes

J Cyst Fibros. 2016 Mar;15(2):251-7. doi: 10.1016/j.jcf.2015.03.013. Epub 2015 Apr 11.


Aims: Early diagnosis of cystic fibrosis (CF) related diabetes (CFRD) is important to improve outcomes. International guidelines recommend an oral glucose tolerance test (OGTT) for all CF patients aged ≥10 years - this approach is controversial. The aim of this study was to develop an effective screening tool and reduce the need for a universal OGTT.

Methods: Adult CF patients (without CFRD) attending an annual review assessment were recruited prospectively (March 2009-July 2012) into two sequential studies - a primary investigative study followed by validation study. All patients underwent an OGTT and were simultaneously screened by predetermined biochemical/clinical criteria to identify their risk of CFRD. A sensitivity/specificity analysis was performed using the World Health Organisation diabetes criteria as gold standard; modifications were made to improve the screening tool's accuracy and determine the optimal screening thresholds. This was tested in the validation study.

Results: 429 patients (primary, n=94; validation, n=335: mean age=31.7 ± 10.4(SD), 43% female, 77% on pancreatic supplements). Primary study: in predicting a positive OGTT, the test sensitivity was 66.7% and specificity 60%. HbA1c was carried over to the validation study as it was the most discriminative (optimal threshold ≥5.8% (40 mmol/mol); receiver operating curve, ROC, score 0.60). Validation study: the number of patients with a normal, impaired and diabetic OGTT was 268(80%), 51(15.2%) and 16(4.8%), respectively. HbA1c provided a test sensitivity, specificity and ROC score of 93.8%, 53.0% and 0.73, respectively.

Conclusions: The use of HbA1c ≥ 5.8%(40 mmol/mol) is an effective tool for CFRD screening and reduced the need for an OGTT by 50.7%.

Keywords: Cystic fibrosis; Cystic fibrosis related diabetes; HbA1c; Oral glucose tolerance test.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adolescent
  • Adult
  • Blood Glucose / metabolism*
  • Cystic Fibrosis / blood
  • Cystic Fibrosis / complications
  • Cystic Fibrosis / diagnosis*
  • Diabetes Mellitus / blood
  • Diabetes Mellitus / diagnosis*
  • Diabetes Mellitus / etiology
  • Early Diagnosis*
  • Female
  • Follow-Up Studies
  • Glucose Tolerance Test
  • Glycated Hemoglobin / metabolism*
  • Humans
  • Male
  • Mass Screening*
  • Middle Aged
  • Prospective Studies
  • Reproducibility of Results
  • Young Adult


  • Blood Glucose
  • Glycated Hemoglobin A
  • hemoglobin A1c protein, human