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HbA 1
c could be used to diagnose diabetes in patients with impaired fasting
glucose (110-125 mg/dl), as if there was a positive result due to a high specificity
or a negative result due to high sensitivity, the carrying out of the OGTT could be
avoided. This way, the interventions of this group of patients could be individualized
better.
In the five localized studies (55-59) on this issue, the OGTT was used or the
medical diagnosis after six years can be used as diagnostic gold standard. Only
two of the studies provided data on the population associated with this matter (58;
59).
The study carried out among the Chinese population (58) only considers 39
patients with altered basal glycaemia, thus it has not been taken into consideration.
A French study (59) was performed on a cohort of 3,627 white race patients
among the general population with low diabetes prevalence and 272 patients with
altered basal glycaemia. The aim of the study was to assess the predictive capacity
of HbA 1
c in the development of diabetes among the general population. This
study has two limitations: loss of patients and assessment of gold standard. From
the initial cohort, 2,820 patients are assessed six years after (77%). The study does
not specify if the physicians carrying out the trial knew the initial classification
of patients.
The glycosylated haemoglobin values from 5.9% patients with Impaired
Fastng Glucose have a 64% sensitivity and 77% specificity, a 2.78 positive likelihood
ratio (+LH) and a 0.46 negative likelihood ratio (-LR). For the diabetes
prevalence of the study (22%) a positive predictive value (PPV) of 44% and a
negative predictive value (NPV) of 88% is achieved.
To summarise, the scarce evidence available cannot give an accurate answer
to our question and thus has some methodological limitations.
An additional limitation of this technique is that, until very recently, no consensus
has been reached (60) on the standardisation of the method and the values
differ according to the technique used by each laboratory.
Diagnostic
test study
II
Evidence summary
II
In a study with methodological flaws, the glycosylated haemoglobin values in 5.9% of
patients with impaired fasting glucose (IFG had a 64% of sensitivity and 77% of specificity,
2.78 +LR and 0.46 -LR- in the prediction of diabetes (59).
Recommendations
B
The use of HbA 1
c is not recommended as a diagnostic test for patients with impaired fasting
glucose.
The performance of studies within our field to assess the diagnostic performance of HbA 1
c
in these situations is recommended.
CLINICAL PRACTICE GUIDELINE ON TYPE 2 DIABETES 43