1-Blood glucose:
In asymptomatic patients, physicians diagnose diabetes mellitus (DM) using the American Diabetes Association (ADA) recommendation of 2 different fasting plasma glucose levels of greater than 125 mg/dL (ie, >6.99 mmol/L). In symptomatic patients, a random glucose of 200 mg/dL suggests diabetes. All finger stick capillary glucose levels must be confirmed in serum or plasma to make the diagnosis.
2- Serum electrolytes
3- Urinalysis for glucose, ketones, and protein:
Urine ketones are not reliable for diagnosing or monitoring DKA. Rather, the plasma acetone, and, specifically, the beta-hydroxybutyrate level, is a reliable indicator of DKA.
4- White blood cell count and blood and urine cultures to rule out infection
5- Glycosylated hemoglobin (Hb) or Hb A1c
* Hb A1c is the stable product of nonenzymatic irreversible glycosylation of the beta chain of Hb by plasma glucose and is formed at rates that increase with increasing plasma glucose levels.
* Most physicians periodically determine Hb A1c to estimate plasma glucose control during the preceding 1-3 months.
* Glycated hemoglobin predicts the progression of diabetic microvascular complications. The reference range for nondiabetic people is 6% in most laboratories.
* Although elevated Hb A1c often indicates existing diabetes, the determination of Hb A1c levels has not been considered a specific diagnostic test for diabetes. In a 2009 report, however, an international expert committee appointed by the ADA, the European Association for the Study of
Diabetes, and the International Diabetes Association recommended Hb A1c assay for the diagnosis of type 1 and type 2 DM.1
In the case of type 1 DM, however, the committee recommended using the test only when the condition is suspected but the classical symptoms of type 1 DM—polyuria, polydipsia, polyphagia, a random glucose level of 200 mg/dL, and unexplained weight loss—are absent.
The committee cited the following advantages of Hb A1c testing over glucose measurement:
1- Captures long-term glucose exposure
2- Has less biologic variability
3- Does not require fasting or timed samples
4-Is currently used to guide management decisions
The committee’s recommendation for a diagnosis of DM is an Hb A1c level of 6.5% or higher, with confirmation from repeat testing (unless clinical symptoms are present and the glucose level is >200 mg/dL).
Glucose measurement should remain the choice for diagnosing pregnant women or if Hb A1c assay is unavailable.
Fructosamine levels also test for glucose levels. Fructosamine is formed by a chemical reaction of glucose with plasma protein and reflects glucose control in the previous 1-3 weeks. This assay, therefore, may show a change in control before Hb A1c and often is helpful when applying intensive treatment and in short-term clinical trials.
Oral glucose tolerance test with insulin levels:
Although this test is usually considered unnecessary to make the diagnosis in type 1 DM, with the dramatic increase of type 2 diabetes in the young population, assessment of insulin secretion may become more important.
To determine whether the individual has type 1 rather than type 2 DM, an insulin and/or C-peptide level below 5 µU/mL, or 0.6 ng/mL, suggests type 1. C-peptide is formed during conversion of proinsulin to insulin.
A high positive titre of glutamic acid decarboxylase antibodies also suggests type 1 DM. An exception is the individual with type 2 DM who presents with a very high glucose, eg, above 300 mg/dL, who temporarily has a low insulin and/or C-peptide level but who will recover insulin production once normal glucose is restored.
1- Islet cell antibodies
2- Thyroxine (T4) and thyroid antibodies
Other Tests
* Intravenous glucose test for possible early detection of subclinical diabetes
* HLA typing may be considered.
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