The Intravenous Glucose Tolerance Test

Abstract

Oral glucose tolerance tests have generally been used to differentiate between diabetes mellitus and the various forms of non-diabetic glycosuria (1).On the basis of such oral tests alterations in carbohydrate metabolism have also been reported in numerous disorders other than diabetes mellitus. These include endocrine, intracranial and hepatic diseases (2), arthritis (3), and convulsive disorders of various types (4). Oral METHODSSixty normal adult subjects were studied. All were in the post-absorptive state and remained in a recumbent position throughout the morning. After a fasting venous blood sample had been obtained, 50 ml. of a 50 per cent solution of glucose in distilled water were injected intravenously during a period of two minutes. Samples of venous blood were obtained at intervals during the next two or three hours. In the majority of cases hourly urine samples were collected as well. A modification of Benedict's macro-method (6) was used for blood sugar analyses, protein-free filtrates of whole blood being employed. Protein was removed by the zinc precipitation method of Somogyi (7), which also removes most of the non-fermentable reducing substances. Rothberg and Evans' (8) tubes were used in the final visual colorimetric comparison. Urine samples were analyzed for glucose by the quantitative method of Benedict (9).The same procedure was applied to 271 patients in the New Haven Hospital. Only a few with outright diabetes were included. The majority were selected either because, on clinical grounds, some abnormality of carbohydrate metabolism was suspected or because they had some one of a variety of disorders reputedly attended by derangement of carbohydrate metabolism.RESULTS

Kinetics of Elimination of Glucose from the Blood during and after a Continuous Intravenous Injection

“…Lack of uniformity in both technique and interpretation is prevalent. The criterion of normality most often appears to be the time interval taken for the elevated blood glucose to regain its pre-injection value (3) or some defined relatively low value (19) or, conversely, the value of blood sugar at a certain time after injection (4). It is evident that such criteria are valid under strictly defined experimental conditions only and lack more universal applicability and deeper physiological meaning.…”

“…Such tests, however, suffer from the disadvantage that the rate of intestinal absorption has an effect on the results, and its variations may entirely overshadow any possible changes in carbohydrate metabolism. This difficulty may, of course, be obviated by administering the sugar by vein, and intravenous tolerance tests have actually been used by many workers (1)(2)(3)(4)(5)(6)(7)(8) . 2 In these tests the sugar has generally been given as a single rapid injection.…”

The Intravenous Glucose Tolerance Test in Pregnancy 1

“…The disadvantages of the oral route of administration of the glucose are many and they have been pointed out by several authors (5)(6)(7)(8)(9). These disadvantages have led to the use of the intravenous route of administration (8,9) as a better test of the ability of the subject to metabolize glucose.…”

“…These disadvantages have led to the use of the intravenous route of administration (8,9) as a better test of the ability of the subject to metabolize glucose. In pregnancy all the objections to the oral route of administration apply as they do in the nonpregnant individual.…”

“…The over-all procedure employed is essentially the same as the one described by Lozner, Winkler, Taylor and Peters (9) who have determined the tolerance of nonpregnant individuals to 25 grams of intravenously administered glucose.…”