Test ID: APGH
Alpha-Subunit Pituitary Tumor Marker, Serum
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Adjunct in the diagnosis of pituitary tumors
As part of the follow-up of treated pituitary tumor patients
Differential diagnosis of thyrotropin-secreting pituitary tumor versus thyroid hormone resistance
Differential diagnosis of constitutional delay of puberty versus hypogonadotrophic hypogonadism
Method Name A short description of the method used to perform the test
Immunochemiluminescent Assay
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Alpha Subunit, HCG
Alpha-HCG (Human Chorionic Gonadotropin)
Alpha-PGH (Pituitary Glycoprotein Hormone)
Alpha-Subunit of Pituitary Glycoprotein Hormones (Alpha-PGH), Serum
Chorionic Gonadotropins, Alpha-Subunit
Glycoprotein Subunit
HCG, Alpha Subunit
Hormone, Alpha-Subunit
PGH (Pituitary Glycoprotein Hormone)
Pituitary Glycoprotein Alpha Subunit
Pituitary Gonadotropins, Alpha-Subunit
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Collection Container/Tube: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross reject |
| Lipemia | Mild OK; Gross OK |
| Icterus | Mild OK; Gross OK |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum Red | Frozen (preferred) | 90 days |
| Refrigerated | 7 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
The 3 human pituitary glycoprotein hormones: luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH), and the placenta-derived chorionic gonadotropin (hCG), are closely related tropic hormones. They signal through G-protein-coupled receptors, regulating the hormonal activity of their respective endocrine target tissues. Each is composed of an alpha- and a beta-subunit, coupled by strong noncovalent bonds.The alpha-subunits of all 4 hormones are essentially identical (92 amino acids; molecular weight [MW] of the "naked" protein:10,205 Da), being transcribed from the same gene and showing only variability in glycosylation (MW of the glycosylated proteins:13,000-18,000 Da). The alpha-subunits are essential for receptor transactivation. By contrast, all the different beta-subunits are transcribed from separate genes, show less homology, and convey the receptor specificity of the dimeric hormones.
Under physiological conditions, alpha- and beta-chain synthesis and secretions are tightly coupled, and only small amounts of monomeric subunits are secreted. However, under certain conditions, coordinated production of intact glycoprotein hormones may be disturbed and disproportionate quantities of free alpha-subunits are secreted. In particular, some pituitary adenomas may overproduce alpha-subunits. Although most commonly associated with gonadotroph- or thyrotroph-derived tumors, alpha-subunit secretion has also been observed in corticotroph, lactotroph, and somatotroph pituitary adenomas. Overall, depending on cell type and tumor size, between 5% to 30% of pituitary adenomas will produce sufficient free alpha-subunits to result in elevated serum levels, which usually fall with successful treatment. Stimulation testing with hypothalamic releasing factors (eg, gonadotropin releasing hormone [GnRH] or thyrotropin-releasing hormone [TRH]) may result in further elevations, disproportionate to those seen in individuals without tumors.
Measurement of free alpha-subunit after GnRH-stimulation testing can also be useful in the differential diagnosis of constitutional delay of puberty (CDP) versus hypogonadotrophic hypogonadism (HH). CDP is a benign, often familial, condition in which puberty onset is significantly delayed, but eventually occurs, and then proceeds normally. By contrast, HH represents a disease state characterized by lack of gonadotropin production. Its causes are varied, including hypothalamic and pituitary inflammatory or neoplastic disorders, a range of specific genetic abnormalities, as well as unknown causes. In children, HH results in complete failure to enter puberty without medical intervention. In children with CDP, in normal pubertal children, in normal adults and, to a lesser degree, in normal prepubertal children, GnRH administration results in increased serum LH, FSH, and alpha-subunit levels. This response is greatly attenuated in patients with HH, particularly with regard to the post-GnRH rise in alpha-subunit concentrations.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
PEDIATRIC
< or =5 days: < or =50 ng/mL
6 days-12 weeks: < or =10 ng/mL
3 months-17 years: < or =1.2 ng/mL
Tanner II-IV*: < or =1.2 ng/mL
ADULTS
Males: < or =0.5 ng/mL
Premenopausal females: < or =1.2 ng/mL
Postmenopausal females: < or =1.8 ng/mL
Pediatric and adult reference values based on Mayo studies.
*Puberty onset (transition from Tanner stage I to Tanner stage II) occurs for boys at a median age of 11.5 (+/-2) years and for girls at a median age of 10.5 (+/-2) years. There is evidence that it may occur up to 1 year earlier in obese girls and in African American girls. For boys, there is no proven relationship between puberty onset and body weight or ethnic origin. Progression through Tanner stages is variable. Tanner stage V (adult) should be reached by age 18.
Interpretation Provides information to assist in interpretation of the test results
In the case of pituitary adenomas that do not produce significant amounts of intact tropic hormones, diagnostic differentiation between sellar- and tumors of nonpituitary origin (eg, meningiomas or craniopharyngiomas) can be difficult. In addition, if such nonsecreting adenomas are very small, then they can be difficult to distinguish from physiological pituitary enlargements.
In a proportion of these cases, free alpha-subunit may be elevated, aiding in diagnosis. Overall, 5% to 30% of pituitary adenomas produce measurable elevation in serum free alpha-subunit concentrations. There is also evidence that an exuberant free alpha-subunit response to thyrotropin-releasing hormone (TRH) administration may occur in some pituitary adenoma patients that do not have elevated baseline free alpha-subunit levels. A more than 2-fold increase in free alpha-subunit serum concentrations at 30 to 60 minutes following intravenous administration of 500 mcg of TRH is generally considered abnormal, but some investigators consider any increase of serum free alpha-subunit that exceeds the reference range as abnormal. TRH testing is not performed in the laboratory, but in specialized clinical testing units under the supervision of a physician.
In pituitary tumors patients with pre-treatment elevations of serum free alpha-subunit, successful treatment is associated with a reduction of serum free alpha-subunit levels. Failure to lower levels into the normal reference range may indicate incomplete cure, and secondary rises in serum free alpha-subunit levels can indicate tumor recurrence.
Small thyrotropin (TSH)-secreting pituitary tumors are difficult to distinguish from thyroid hormone resistance. Both types of patients may appear clinically euthyroid or mildly hyperthyroid and may have mild-to-modest elevations in peripheral thyroid hormone levels along with inappropriately (for the thyroid hormone level) detectable TSH, or mildly-to-modestly elevated TSH. Elevated serum free alpha-subunit levels in such patients suggest a TSH secreting tumor, but mutation screening of the thyroid hormone receptor gene may be necessary for a definitive diagnosis.
Constitutional delay of puberty (CDP), is a benign, often familial condition, in which puberty onset is significantly delayed, but eventually occurs and then proceeds normally. By contrast, hypogonadotrophic hypogonadism (HH) represents a disease state characterized by lack of gonadotropin production. Its causes are varied, ranging from idiopathic over specific genetic abnormalities to hypothalamic and pituitary inflammatory or neoplastic disorders. In children, it results in complete failure to enter puberty without medical intervention. CDP and HH can be extremely difficult to distinguish from each other. Intravenous administration of 100 mcg gonadotropin releasing hormone (GnRH) results in much more substantial rise in free alpha-subunit levels in CDP patients, compared with HH patients. A >6-fold rise at 30 or 60 minutes post-injection is seen in >75% of CDP patients, while a less than 2-fold rise appears diagnostic of HH. Increments between 2-fold and 6-fold are non diagnostic.
GnRH testing is not performed in the laboratory, but in specialized clinical testing units under the supervision of a physician.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
False-positive elevations in serum free alpha-subunit levels may be seen in some women if blood specimens are drawn within 24 hours of ovulation.
Patients with end-stage renal failure may have serum free alpha-subunit concentrations of up to 6-times the upper limit of reference range.
Elevated alpha-subunit results on patients with elevated thyrotropin (TSH) should be interpreted with caution due to TSH cross-reactivity with the assay.
Assisted reproduction involving ovarian hyperstimulation or in vitro fertilization may be associated with the elevation in serum free alpha-subunit levels.
Pregnancy is associated with very substantial, physiological elevations in serum free alpha-subunit levels, paralleling chorionic gonadotropin (hCG) secretion. This test should not be ordered on pregnant patients.
Thyrotropin-releasing hormone (TRH) and gonadotropin releasing hormone (GnRH) testing are not performed in the laboratory, but in specialized clinical testing units under the supervision of a physician.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Preissner CM, Klee GG, Scheithauer BW, Abboud CF: Free alpha subunit of the pituitary glycoprotein hormones. Am J Clin Pathol 1990;94:417-421
2. Mainieri AS, Viera JGH, Elnecave RH: Response of the free alpha-subunit to GnRH distinguishes individuals with "functional" from those with permanent hypogonadotropic hypogonadism. Horm Res 1998;50:212-216
3. Samejima N, Yamada S, Takada K, et al: Serum alpha-subunit levels in patients with pituitary adenomas. Clin Endocrinol 2001:54:479-484
4. Mainieri AS, Elnecave RH: Usefulness of the free alpha-subunit to diagnose hypogonadotropic hypogonadism. Clin Endocrionol 2003;59:307-313
5. Socin HV, Chanson P, Delemer B, et al: The changing spectrum of TSH-secreting pituitary adenomas: diagnosis and management in 43 patients. Eur J Endocrinol 2003;148:433-442
Method Description Describes how the test is performed and provides a method-specific reference
Alpha-subunit pituitary glycoprotein hormone is measured using an immunochemiluminescent assay (ICMA) sandwich procedure. Standards, controls, and specimens are first incubated with monoclonal antibody-coated beads for 2 hours. After washing, a different monoclonal antibody labeled with acridinium ester is added and incubated for 1 hour. After washing, the beads (with attached labeled antibody) are counted in a luminometer. The resulting chemiluminescent light units are directly proportional to the amount of alpha-subunit pituitary glycoprotein hormone present in the sample. (Unpublished Mayo method)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Tuesday; 11 a.m.
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
83520
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 9003 | AlphaSubunit Pituitary Tumor Marker | 14170-5 |
External
link
PDF
document
Excel
document
Word
document