The added value of oral glucose tolerance testing in pre-diabetes

With the increased acceptance of glycated hemoglobin measurement as the test of choice for the diagnosis and detection of diabetes, doubts which surround the use of the oral glucose tolerance test (OGTT) in detecting disturbances in glucose levels have become even more apparent. Metabolically, there are still arguments to use the OGTT. Epidemiological studies though, have not always supported the efficacy of the OGTT when used for screening in obese patients. In our opinion, current evidence suggests an additive value of the OGTT, its main advantage being the ability to detect stages of pre-diabetes more accurately than HbA1c and the ability to investigate postprandial glucose levels in a physiological way.     

The oral glucose tolerance test (OGTT) revisited

The oral glucose tolerance test (OGTT) has been the mainstay for diagnosing diabetes for decades. Recently, the American Diabetes Association (ADA) suggested abandoning the OGTT, while resorting to a simpler screening test, exclusively based on baseline fasting blood glucose concentration.This review article rewinds the history of OGTT and its recent advancements, and compares its power in detecting early diabetes with that of fasting blood glucose alone.The key point is that there are more diabetics originating from a population with normal fasting blood glucose than from subjects with impaired fasting glucose, those who can be detected by the new ADA recommendations. Conversely, the OGTT detects more efficiently early diabetes as well as subjects with IGT, as the glycemia at the second hour seems crucial as a diagnostic tool. We discuss the different significance of fasting versus second hour glycemia during OGTT, according to different mechanisms of glucose homeostasis.Finally, we provide recent evidence on very simple additional information that can be obtained from the OGTT, which renders this test even more useful, discussing pathophysiologic significance.     

去氨加压素兴奋试验在库欣综合征中的诊断价值

研究表明,血管加压素是促肾上腺皮质激素的一种有效促泌剂,去氨加压素作为血管加压素的一种长效类似物,可用于促肾上腺皮质激素依赖性库欣综合征的诊断与鉴别诊断,排除假性库欣综合征与非促肾上腺皮质激素依赖性库欣综合征。此外,去氨加压素兴奋试验还可作为库欣病患者（术前去氨加压素兴奋试验为阳性反应者）术后随访的一个生化指标。     

Diagnostic value of fasting capillary glucose,fructosamine and glycosylated haemoglobin in detecting diabetes and other glucose tolerance abnormalities compared to oral glucose tolerance test

New diagnostic criteria for diabetes mellitus recommend lowering of the fasting plasma glucose to 7.0 mmol/l. In contrast to recommendations of the American Diabetes Association (AA). WHO recommends using the oral glucose tolerance test (OGTT) in clinical practice. In this study, based on OGTT results and WHO 1998 criteria, we determined if measuring fasting capillary glycaemia (FCG) along with fructosamine and/or glycosylated haemoglobin allows the detection of glucose tolerance abnormalities better than FCG alone. OGTT was performed in 538 patients. Serum fructosamine was determined in 480 of the patients, and glycosylated haemoglobin in 234 of the patients. According to WHO 1998 criteria, the patients were divided into groups due to glucose tolerance abnormalities. Fructosamine correlated stronger with 2-h post-load glucose concentrations than with FCG. HbA1c correlated stronger with FCG than with 2-h post-load glucose. Combined use of fructosamine and FCG predicted 2-h post-load glucose better than combined use of FCG and HbA1c. Receiver operating characteristic curve analyses showed that FCG was the best criterion in discriminating diabetes. Combined use of FCG and fructosamine slightly improved the ability to discriminate glucose tolerance abnormalities from normal glucose tolerance. FCG is the most effective predictor of 2-h post-load glucose and the best criterion for discriminating diabetes and other glucose tolerance abnormalities from normal glucose tolerance. Fructosamine is a potentially useful post-load glycaemia index. OGTT is irreplaceable in identification of patients with high post-load glycaemia. Received: 14 March 2001 / Accepted in revised form: 19 December 2001     

The value of glycosylated haemoglobin as a substitute for the oral glucose tolerance test in the detection of impaired glucose tolerance (IGT).

In a prospective study of South African Indian subjects with IGT, glycosylated hemoglobin [specifically HbA1 (HbA1(a+b+c)] and its relationship to the oral glucose tolerance test (OGTT) was studied in 128 study subjects who were classified IGT a year previously (Year 0 of study) and in 64 control subjects. At Year 1 of the study, the standard 75-g OGTT was performed on all subjects; study subjects were further divided into three groups based on World Health Organisation criteria [Normal (N), impaired glucose tolerance (IGT), diabetes mellitus (D)]. HbA1, a glycosylated hemoglobin (GHb), was measured by a cation-exchange microchromatographic method. Based on OGTT results, 47 of the 128 study subjects were classified IGT, 41 diabetes (newly-diagnosed diabetes) and 40 subjects had normal glucose tolerance. Mean GHb was significantly higher in the D group (7.61 +/- 1.76%) compared to the control group (6.99 +/- 1.22%) and the N group (6.9 +/- 1.12%), respectively (P less than 0.05); there was no significant difference between the IGT group (7.48 +/- 1.44%) and each of the other three groups. Compared to the OGTT, GHb was relatively insensitive in the diagnosis of IGT or diabetes mellitus: only 17% of the IGT group and 26.8% of the D group has elevated GHb values; the specificity of GHb as a measure of normal glucose tolerance was 85.9%. The majority of subjects, irrespective of the category of glucose tolerance, had GHb levels within the normal range and there was marked overlap between the four groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

口服葡萄糖耐量试验重复性调查及其临床应用价值

目的调查75g口服葡萄糖耐量试验（OGTT）诊断糖代谢异常的重复性。方法259例既往未诊断糖尿病的受试人群（男152例,女107例）间隔2～3周重复进行两次OGTT。结果OGTT总体重复率为56．4％。根据第一次OGTT结果把人群分为糖耐量正常、糖调节受损（IGR）和糖尿病3组,其重复率分别为91．2％、37．5％和63．8％,组间比较差异有统计学意义（P〈0．05）。根据人群所含的代谢异常组分个数的不同分组,发现具有2个代谢异常组分的人群OGTT重复率明显低于代谢异常组分小于或大于2个的人群（P值均〈0．05）。两次OGTT结果为正常．异常组的年龄、血压、心率和腰臀围比明显高于正常-正常组（P值均〈0．05）,异常-异常组的腰围和TG高于、HDL-C低于正常-异常组,其他临床特征差异无统计学意义。结论OGTT总体重复率较低,在IGR人群和中度代谢异常人群中尤为显著。与正常人群相比,只要一次OGTT显示为异常的人群就具有较多的心血管病危险因子,因此虽然OGTT重复性较低,但是对糖代谢异常的筛查仍具有重要的实践意义。     

Evaluation of oral glucose tolerance test results in pregnancy

Oral glucose tolerance and insulin response to glucose were analysed in 124 pregnant women during the fourth quartile of pregnancy. Employing different criteria for the detection of glucose intolerance, 9% to 21% of women were abnormal, and using the H index 43% would have been declared "diabetic". There was no evidence of a progressive change in the glucose curve detectable by the H index within the fourth quartile of pregnancy. There was no association between actual or potential fetal morbidity and any of the interpretative criteria employed. It is concluded that the oral glucose tolerance test should be interpreted with caution if non-pregnant criteria of abnormality are employed.     

Minor physiological relevance of oral glucose tolerance test

The physiological relevance of the oral glucose tolerance test was evaluated in ten healthy nonobese subjects and nine subjects with slightly impaired glucose tolerance. In random order, all subjects received a 50 g oral glucose tolerance test or a standardized breakfast meal of equivalent carbohydrate content. Changes in plasma glucose, insulin, and pancreatic glucagon concentrations were measured. In both groups, plasma glucose increased significantly during the oral glucose tolerance test and the meal test but the incremental glucose area (0-60 min) of the oral glucose tolerance test was about 350% and 120% greater than that of the mean test (p less than 0.001) in the normals and the patients with impaired glucose tolerance, respectively. In both groups, insulin responded almost similarly to the oral glucose tolerance test and the meal test whereas plasma glucagon declined significantly during the oral glucose tolerance test only (p less than 0.001). Glucagon remained unchanged during the meal test in the normals and increased slightly (p less than 0.05) in the group with impaired glucose tolerance. These data show that the response of glucose, insulin and glucagon to an oral glucose tolerance test in various respects is different to that obtained by the more physiological stimulation with a breakfast meal.     

The diagnostic value of the oral pancreatic function test.

An oral pancreatic function test (PFT) using the synthetic peptide N-benzoyl-L-tyrosyl-p-aminobenzoic acid can assess pancreatic exocrine function, since urinary recovery of the ingested dose is an indirect index of chymotryptic activity. We have studied 34 subjects using this oral PFT, which correctly distinguished the control group (8 subjects) from the pancreatitis group (10 patients), results correlating well with Lundh test findings. However, the test was falsely abnormal on 9 out of 16 occasions in patients with bowel or liver disease. We therefore conclude that the present test cannot distinguish small-bowel disease from pancreatic disease, which is often the diagnostic problem, and is also frequently falsely abnormal in the presence of chronic liver disease.     

The oral glucose tolerance test: An objective method of interpretation

Summary Oral glucose tolerance test results from a positively-skewed, unimodal distribution were analyzed in such a way as to uncover a natural division within the set of results for each time point. The division in results was obtained from a break in the curve formed when plasma glucose concentration was plottedvs the percentile of the population described by those concentrations. The percentile at which the break occurs separated normal from abnormal glucose concentrations objectively. Previously natural divisions between normal and abnormal glucose concentrations had been found only in bimodal distributions from atypical populations such as the Pima Indians and Nauruans of Micronesia. The glucose concentrations at which separations in our unimodal distribution occur compare well with the available data from the atypical populations. According to one measure of reliability, the 3-h time point was more effective than the more commonly utilized 2-h point in distinguishing normal from abnormal plasma glucose concentration.     

口服葡萄糖耐量试验临床应用的争议与共识

随着人们生活方式的改变,2型糖尿病和糖耐量受损(IGT)的发病率日益增加。流行病学资料显示有相当一部分新发的2型糖尿病患者因没有得到及时诊治而导致其并发症的发生[1],同时IGT被认为是糖尿病的独立危险因子,与心血管疾病的发生密切相关[2],早期发现并进行干预可以明显减少糖尿病的发生,因此糖尿病和IGT的早期筛查极为重要。口服葡萄糖耐量试验(OGTT)被WHO推荐为目前筛查糖尿病和IGT的标准方法,但就其在临床实践和流行病学中的地位还存在争议:美国糖尿病学会(ADA)由于其操作不便、重复性差、耗资较大,所以不推荐常规使用;国际糖尿…     

Paradoxical release of growth hormone during oral glucose tolerance test in patients with abnormal glucose tolerance

Oral glucose tolerance tests were performed on 24 patients characterized as having abnormal glucose tolerance (AGT) and on 27 control subjects. Serums for glucose, growth hormone and insulin determinations were serially obtained for 4 hr after glucose administration. As serum glucose declined 2 hr or more after glucose ingestion a rise in growth hormone, as has been previously described, was observed in 40% of control subjects and 12% of AGT patients. However, of interest was a paradoxical early increase in growth hormone levels noted in 44% of lean AGT subjects occurring during the first 2 hr of the test with glucose levels rising. This response was seen in only one of 8 obese patients with AGT and in none of the control subjects. An abnormality in the hypothalamic glucose receptors in the ventromedial nucleus is a possible explanation for the changes observed. It is possible that this early inappropriate increase in growth hormone release may in some nonobese subjects with AGT contribute to the abnormal oral glucose tolerance tests observed.     

血糖正常的高血压患者做葡萄糖耐量试验的临床意义

目的：探讨对空腹血糖正常的高血压患者进行葡萄糖耐量试验（OGTT）的意义。方法：选择既往无糖代谢异常病史，空腹血糖〈5．6mmol／L，确诊原发性高血压的成人患者；行OGTT2h血糖测定，如果OGTT2h血糖≥11．1mmol／L，再次行OGTT以排除糖尿病。同时观察年龄，入院时血压、体重指数、血肌酐、血尿酸、甘油三酯、高密度脂蛋白等参数的改变。结果：本组266例患者中检出糖耐量减低者（OGTT2h血糖≥7．8mmol／L）共98例（36．8％），其中确诊2型糖尿病29例（OGTT2h血糖≥11．1mmol／L），占10．9％。结论：所有空腹血糖正常的高血压患者均应进行OGTT，以发现可能的糖代谢异常，使患者能得到早期干预，更显著地降低心血管事件发生的风险。