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Test Code GLP Glucagon, Plasma

Reporting Name

Glucagon, P

Useful For

Diagnosis and follow-up of glucagonomas and other glucagon-producing tumors

 

Assessing diabetic patients with problematic hyper- or hypoglycemic episodes (extremely limited utility)

 

Glucagon is routinely measured along with serum glucose, insulin, and C-peptide levels, during the mixed-meal test employed in the diagnostic workup of suspected postprandial hypoglycemia. However, it plays only a minor role in the interpretation of this test.

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Plasma EDTA


Specimen Required


Collection Container/Tube: Lavender top (EDTA)

Submission Container/Tube: Plastic vial

Specimen Volume: 2 mL

Collection Instructions:

1. Fasting

2. Prechill tube at 4 degrees C before drawing the specimen.

3. Draw the prechilled tube, and process as follows:

a. After drawing specimen, chill tube in wet ice for 10 minutes.

b. Centrifuge in a refrigerated centrifuge or in chilled centrifuge cup.

c. Immediately after centrifugation, remove plasma, place in a plastic transport vial (Supply T465), and freeze.

Forms: If not ordering electronically, complete, print, and send an Oncology Test Request Form (T729) with the specimen

(http://www.mayomedicallaboratories.com/it-mmfiles/oncology-request-form.pdf)


Specimen Minimum Volume

0.45 mL

Specimen Stability Information

Specimen Type Temperature Time
Plasma EDTA Frozen 90 days

Reference Values

≤6 hours: 100-650 pg/mL

1-2 days: 70-450 pg/mL

2-4 days: 100-650 pg/mL

4-14 days: declining gradually to adult levels

>14 days: ≤80 pg/mL (range based on 95% confidence limits)

Glucagon levels are inversely related to blood glucose levels at all ages. This is particularly pronounced at birth and shortly thereafter, until regular feeding patterns are established. This explains the higher levels immediately after birth, which then first fall as the glucagon release mobilizes the infant's glucose stores, then rise again as stores are depleted, finally normalizing towards adult levels as regular feeding patterns are established.

Day(s) and Time(s) Performed

Monday, Thursday; 10 a.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

82943

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GLP Glucagon, P 2338-2

 

Result ID Test Result Name Result LOINC Value
9358 Glucagon, P 2338-2

Clinical Information

Glucagon is a single-chain polypeptide of 29 amino acids that is derived from a larger precursor peptide (big plasma glucagon), which is cleaved upon secretion. The main sites of glucagon production are the hypothalamus and pancreatic alpha-islet cells. The function of hypothalamic glucagon is incompletely understood and currently no clinical disorders of hypothalamic glucagon function have been defined. Pancreatic islet glucagon is secreted in response to hypoglycemia, with resultant increases in blood glucose concentration. Glucagon's hyperglycemic effect is produced by stimulating hepatic glycogenolysis and gluconeogenesis; it has no effect on muscle glycogen. Once blood-glucose levels have normalized, glucagon secretion ceases.

 

Excessive glucagon secretion can lead to hyperglycemia or aggravate preexisting hyperglycemia. Excessive and inappropriate glucagon secretion can sometimes be observed in diabetes, in particular during ketoacidosis, and can complicate management of the disorder. In rare cases, it also can occur in tumors of the pancreatic islets (glucagonoma); carcinoid tumors and other neuroendocrine neoplasms and hepatocellular carcinomas. Patients with glucagon-secreting tumors may present with classic glucagonoma syndrome, consisting of necrolytic migratory erythema, diabetes, and diarrhea, but also can have more subtle symptoms and signs.

 

Decreased or absent glucagon response to hypoglycemia can be seen in type I diabetes (insulin-dependent diabetes) and can contribute to severe and prolonged hypoglycemic responses.

Interpretation

Elevated glucagon levels in the absence of hypoglycemia may indicate the presence of a glucagon-secreting tumor. Successful treatment of a glucagon-secreting tumor is associated with normalization of glucagon levels.

 

Inappropriate elevations in glucagon levels in hyperglycemic type I diabetic patients indicate that paradoxical glucagon release may contribute to disease severity. This can be observed if insulin treatment is inadequate and patients are ketotic. However, glucagon measurement plays little, if any, role in the diagnostic workup of diabetic ketoacidosis, which is based on demonstrating significantly elevated plasma or serum glucose (>250 mg/dL), circulating ketones (beta-hydroxy butyrate), and acidosis (typically with increased anion gap).

 

In diabetic patients, low glucagon levels (undetectable or in the lower quartile of the normal range) in the presence of hypoglycemia indicate impairment of hypoglycemic counter-regulation. These patients may be particularly prone to recurrent hypoglycemia. This can be a permanent problem due to islet alpha-cell destruction or other, less well understood processes (eg, autonomous neuropathy). It can also be functional, most often due to over tight blood-glucose control, and may be reversible after decreasing insulin doses.

Clinical Reference

1. Sherwood NM, Krueckl SL, McRory JE: The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily. Endocrin Rev 2000 Dec;21(6):619-670

2. Tomassetti P, Migliori M, Lalli S, et al: Epidemiology, clinical features and diagnosis of gastroenteropancreatic endocrine tumours. Ann Oncol 2001;12 Suppl 2:S95-99

3. Cryer PE: Hypoglycemia risk reduction in type 1 diabetes. Exp Clin Endocrinol Diabetes 2001;109 Suppl 2:S412-423

4. Jhiang G, Zhang BB: Glucagon and regulation of glucose metabolism. Am J Physiol Metab 2003;284:E671-E678

5. vanBeek AP, de Haas ER, van Vloten WA, et al: The glucagonoma syndrome and necrolytic migratory erythema: a clinical review. Eu J Endocrinol 2004;151:531-537

Analytic Time

2 days

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross OK

Icterus

Mild OK; Gross OK

Other

NA

Method Name

Immunoassay Following Extraction