CRITERIA FOR AND INTERPRETATION OF NORMAL GLUCOSE TOLERANCE TESTS

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Abstract
Most of the errors commonly encountered in the glucose tolerance tests may be avoided by the use of true blood sugar detns. on venous blood in ambulant individuals. The criteria for normality are a fasting level of 100 mg.% or less, increase to a maximum of 150 mg. or less, and a return to 100 mg. or less, 2 hrs. after the ingestion of 100 g. of glucose. Diminished tolerance is indicated by elevation of both the maximal and the 2-hr. values. Results with the Folin-Wu method include variable amts. of non-glucose reducing substances, hence are not as dependable as a true blood sugar method. Arterial blood sugar detd. with capillary blood is not as valuable as venous blood sugar because absorption by the peripheral tissues, which represents part of the normal metabolism of sugar, makes the venous value much lower. Marked arteriovenous blood sugar differences reflect the activity of the peripheral tissues (muscle and skin) in disposing of glucose and indicate that its removal from the blood is not carried out solely by the liver. The absorption of glucose from the small intestine is more accurately recorded by the arterial blood sugar. Renal threshold obviously involves arterial blood sugar. Contrary to accepted beliefs, based largely on hospitalized individuals and bed rest, the aged show no impairment of glucose tolerance. The prevalent idea that the renal threshold is lower during the fall of a glucose tolerance curve based on venous blood levels, than during its rise, is probably incorrect, because arterial blood sugar often rises from the half hr. to the hr. mark, during which the venous blood sugar falls.

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