Starvation (depletion of liver glycogen)
Limitations
In premenopausal women, the test can be performed at any phase of the menstrual cycle, because there are no cycle effects on the hypothalamic–pituitary–adrenal axis response to insulin-induced hypoglycemia.
Almost all patients have some degree of perspiration. If the patient does not perspire, the adequacy of the stress stimulus must remain suspect irrespective of the serum glucose concentration.
Most patients also have a hyperactive precordium (but not tachycardia or hypotension, because they are supine) and feelings of hunger, drowsiness, detachment, or anxiety. The last is common and sometimes severe, and many patients find this an unpleasant experience.
Patients with primary or secondary adrenal insufficiency or long-standing DM have an impaired compensatory response to hypoglycemia.
The criteria for a normal serum cortisol response ranged from 18 to about 22 μg/dL in multiple studies. Ideally, reference ranges would be determined locally, but this is rarely done in practice. If serum cortisol reaches this level, it is unimportant whether hypoglycemia was adequate. On the other hand, failure to reach this level is indicative of an inadequate response only if the serum glucose fell to 35 mg/dL or less. If this was not achieved, the stimulus was inadequate and the test must be repeated. It is the serum cortisol concentration that is achieved rather than the increment that is important.
INSULIN-LIKE GROWTH FACTOR–BINDING PROTEIN-3 (IGFBP-3)
Definition
This 264-amino-acid peptide (molecular weight, 29 kDa) is produced by the liver. It is the most abundant of a group of IGFBPs that transport and control bioavailability and half-life of insulin-like growth factors (IGFs), in particular IGF-I. In addition to its IGF-binding function, IGFBP-3 also exhibits intrinsic growth-regulating effects that are not yet fully understood but have evoked interest with regard to a possible role of IGFBP-3 as a prognostic tumor marker. Other name: somatomedin C–binding protein.
Normal range:
see Table 16.49.
TABLE 16–49. Normal Ranges for IGFBP-3
Use
