Authors' objectives

To determine whether a glycosylated haemoglobin (HbA1c) level can be used instead of an oral glucose tolerance test (OGTT) to diagnose diabetes mellitus.

Searching

MEDLINE was searched from 1966 to 1994 for articles in any language with English abstracts. No search strategy was reported. The references of retrieved articles and the files of one reviewer were checked for further studies.

Study selection

Assessment of study quality

The principal investigators of the included studies were contacted for data for the analysis. All available data, published and unpublished, were provided on studies included in the analysis. No process of data checking was described. Three studies for which there was no response from the principal investigator, and 13 for which data could not be obtained, were excluded from the analysis.

Data extraction

Data from the original studies were transferred to a new database by one reviewer and checked against the original data by a second. Patient characteristics, sample size, prevalence of diabetes, details and results of the OGTT, and HbA1c levels were recorded.

Methods of synthesis

Results of the review

Of the 34 studies eligible for inclusion, 31 authors responded when contacted and 18 of these provided relevant information. Therefore, 18 studies (11,276 patients) were initially included. However, because HbA1c showed the least variance in normal individuals, only data from the 8,984 participants (in 10 studies) who had HbA1c levels measured were included.

In those patients whose OGTT result met the criteria for diabetes, the sensitivity, specificity and positive predictive values (assuming a diabetes prevalence of 6%) were: for an HbA1c level of mean HbA1c plus 2 standard deviations (SDs), 66, 98 and 63%, respectively;

for an HbA1c level of mean HbA1c plus 3 SDs, 48, 100 and 90%, respectively; and

for an HbA1c level of mean HbA1c plus 4 SDs, 36, 100 and 97%, respectively.

The diagnoses of diabetes by HbA1c level and the results of the OGTT were not equivalent.

A proposed HbA1c cutpoint of 7% was derived from the trimodal model. Of those patients with an HbA1c level of at least 7%, 89.1% had diabetes, 7.1% had IGT and 3.8% were normal.

Authors' conclusions

An HbA1c level of 7.0% or higher often requires pharmaceutical intervention and is most often associated with the diagnosis of diabetes by WHO standards. An HbA1c level below 7.0% would usually be treated with diet and exercise, regardless of the diagnosis of IGT or diabetes by OGTT. Therefore, the measurement of HbA1c levels may represent a reasonable approach to identifying treatment-requiring diabetes.

CRD commentary

The review addressed a clear and relevant question and limited inclusion criteria were defined. The search strategy was limited and it is therefore possible that relevant studies may have been overlooked. In addition, no attempt to identify data from unpublished studies was reported. The principal investigators of all 34 potentially relevant studies were contacted. However, the process of selecting relevant studies and obtaining and checking the data was unclear. From a total of 13,628 participants in the original 34 studies, only 8,984 participants from 10 studies were included in the analysis. This means that approximately one third of the potentially relevant data were not included in the analysis; such a loss of data could potentially have a substantial effect on the findings of the review. The authors' conclusions, whilst probably valid, make substantial reference to the clinical application of HbA1c levels in practice, an area not addressed by the review.

Implications of the review for practice and research

Practice: The authors stated that to confirm the diagnosis of diabetes, a positive test should be repeated.

Research: The authors did state any implications for further research.

Funding

American Diabetes Association.

Bibliographic details

Peters A L, Davidson M B, Schriger D L, Hasselblad V. A clinical approach for the diagnosis of diabetes mellitus: an analysis using glycosylated hemoglobin levels. JAMA 1996; 276(15): 1246-1252. [PubMed: 8849753]

Indexing Status

Subject indexing assigned by NLM

MeSH

Diabetes Mellitus /blood /diagnosis; Glucose Tolerance Test; Hemoglobin A, Glycosylated /analysis; Humans; Models, Biological; Reproducibility of Results; Sensitivity and Specificity

AccessionNumber

11996008476

Database entry date

31/01/2005

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.