American Association for Clinical Chemistry
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NACB - Scientific Shorts
NACB - Scientific Shorts (formerly NACB Blog)
By Douglas Stickle, PhD

Current standards of medical practice from the American Diabetes Association (ADA) (1) and the parallel guidelines from NACB (2) include relatively straightforward criteria for diagnosis of diabetes. Guidelines also include instructions and interpretations for the oral glucose tolerance test (OGTT), where needed for diagnosis of diabetes, and for a combined screening and diagnosis OGTT for gestational diabetes, which is recommended for all not-known-to-be-diabetic pregnancies at 24-28 weeks gestation (Table 1).

Despite the existence of these very up-to-date (2011) guidelines for gestational diabetes OGTTs, requests for gestational OGTTs at our institution come primarily from physicians who expect testing to occur according to 2001 guidelines of the American College of Obstetricians and Gynecologists (ACOG) (3). These comprise two separate tests for screening and diagnosis (Table 2).

In providing both ADA and ACOG OGTTs -- which are conducted primarily by outpatient phlebotomy services at our institution -- we thus require four separate procedures (ADA OGTT, ADA gestational OGTT, ACOG gestational OGTT screen, ACOG diagnostic gestational OGTT) and availability of three separate glucola drinks (50 g, 75 g, and 100 g). One disadvantage of the multiplicity of available tests is that it leads to a certain regular rate of misorders, with result of physicians not always obtaining results according to their desires and expectations.

The ACOG and ADA criteria for diagnosis of gestational diabetes are obviously not aligned. The need for two OGTTs to diagnose gestational diabetes according to ACOG criteria would appear to be a disadvantage for patients relative to the single test recommended via the ADA guidelines. Additionally, note that patient fasting is not required for the ACOG screening OGTT. That seems counterproductive to purpose -- a built-in, results-muddling preanalytical variable (4, 5). Considering the time and effort that a patient must spend for any appointment, my opinion is that this lack of control of the initial conditions of the test represents a less-than-optimum service to the patient.

I have posted on-line commentary at our institution concerning the differences between the ADA and ACOG tests and advocating use of the more modern and simpler guidelines from ADA. From the perspective of physicians ordering the ACOG test, however, they are already "with the program" within their own formally sanctioned standard of care. Yet the availability of different tests and criteria for diagnosis of gestational diabetes raises the general issue of non-uniformity of standard of care within our institution. However, this is not an area where the laboratory can dictate practice. It will be interesting to see whether revised ACOG guidelines will ultimately appear, and whether they will align with ADA.

Although a fasting glucose value may be sufficient to diagnose diabetes according to ADA, we have suspended the practice of evaluating fasting glucose prior to administration of the glucose load, for two reasons: 1. physicians usually want the test to proceed anyway (explanation: they are choosing to interpret results as if measurements within one OGTT are independent measurements), and 2. evaluation of fasting glucose prior to glucose load is not part of either the ACOG guidelines or the WHO procedure (6) to which ADA guidelines refer. It would seem unwise to pour glucose into someone who is patently diabetic upon fasting (e.g., fasting glucose > 200 mg/dL), but there are no formal guidelines that I am aware of concerning suspension of testing based on fasting measurement -- hyperglycemia is simply listed as a known risk factor for OGTT according to WHO. Should a glucose load have a fasting glucose measurement evaluated beforehand?

Last, having just left the AACC meeting in Atlanta, home of Coca-Cola: where does the ADA OGTT 75 g glucose stand relative to a Coke? A 0.5 L Coke contains 55 g of sugar (usually, mixed fructose and glucose; sometimes, sucrose). So, sugar content of an ADA OGTT is approximately equal to that of 0.7 L of Coke.

Tables 1 and 2



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Posted by
On 11/2/2011

It is my understanding that using ADA GDM screening guidelines would NOT result in a significant increase in GDM numbers. When screening & testing is performed during the first trimester, at the first prenatal visit as recommended, the diagnosis would be occult DMII not GDM. This diagnosis in the first trimester of pregnancy and its treatment is significantly different from screening/diagnosis/treatment of GDM at 24-28wks. Uncontrolled hyperglycemia during the first trimester poses increased risk of many complications including birth defects. This is NOT the case with GDM. I realize that your article addresses the differences in 24-28 wk OGTT testing, but early screening is so important for the patient population our clinic sees. I wish ACOG would recommend the ADA early screening recommendations! Anne Willingham, RN, BSN Seattle, WA

Posted by
On 9/13/2011

Michael: The ordering physicians here include but are not limited to obstetric physicians. They prefer use of ACOG diagnostic criteria for gestational diabetes. Actually, it is not a preference, it's a requirement from their perspective, so as not to be doing anything different from other obstetric physicians. -Doug Stickle

Posted by
On 9/8/2011

Dear Dr. Stickle, In your institution, do you have obstetric physicians, internists who tend to the medical disorders of pregnant women? Do they have a preference for diagnostic criteria for gestational diabetes? Michael Metz, North Adelaide, South Australia

Posted by
On 8/30/2011

I wish to call readers' attention to Dr. Grenache's recent blog entry on this same topic. See: -Doug Stickle

Posted by
On 8/30/2011

Dear Dr. Grenache: Thank you very much for bringing to our attention to this recent ACOG update on the topic (September 2011). I had not yet seen it. We have little utilization of ADA GDM OGTT at our facility. You're right; its use would likely engender an increase in incidence of GDM. A discussion of this aspect of the ADA's recommendations is given in the ADA guidelines. Doug Stickle

About the Author
Douglas Stickle, PhD
Douglas Stickle, PhD 


1. American Diabetes Association. Standards of Medical Care in Diabetes—2011.
Diabetes Care 2011; 34, Supplement 1: S11-S61.

2. Sacks DB et al. Position Statement Executive Summary: Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus. Diabetes Care 2011;34:1419-1423.

3. American College of Obstetricians and Gynecologists. Gestational Diabetes. ACOG Practice Bulletin Clinical Guidelines for Obstetrician-Gynecologists. Number 30, September 2001.

4. Coustan DR et al. Should the fifty-gram, one-hour plasma glucose screening test for gestational diabetes be administered in the fasting or fed state? Am J Obstet Gynecol 1986 May;154(5):1031-5.

5. Lewis GF et al. Prior feeding alters the response to the 50-g glucose challenge test in pregnancy. The Staub-Traugott effect revisited. Diabetes Care. 1993 Dec;16(12):1551-6.

6. World Health Organization. Definition, Diagnosis and Classification of Diabetes Mellitus and its Complications. World Health Organization, Dept Noncommunicable Disease Surveillance, Geneva, 1999.