Test ID: GABA
Gabapentin, Serum
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
Monitoring serum concentration of gabapentin, particularly in patients with renal disease
Assessing compliance
Assessing potential toxicity
Method Name A short description of the method used to perform the test
Enzyme-Multiplied Immunoassay Technique (EMIT)
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
Neurontin (Gabapentin)
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.
Container/Tube: Red top
Specimen Volume: 1 mL
Collection Instructions:
1. Draw specimen immediately before next scheduled dose.
2. Spin down within 2 hours of draw.
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 reject |
| Icterus | Mild OK; Gross reject |
| Other | Serum gel tube or whole blood |
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 | Refrigerated (preferred) | 14 days |
| Ambient | 14 days | |
| Frozen | 14 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Gabapentin is an antiepileptic drug that is effective in treating seizures, neuropathies, and a variety of neurological and psychological maladies. Although designed as a gamma amino butyric acid (GABA) analogue, gabapentin does not bind to GABA receptors, nor does it affect the neuronal uptake or content of GABA; its precise mechanism of action is not known.
Gabapentin circulates essentially unbound to serum proteins. Unlike most antiepileptic drugs, gabapentin does not undergo hepatic metabolism; it is eliminated almost entirely by renal excretion with a clearance that approximates the glomerular filtration rate. The elimination half-life is 5 to 7 hours in patients with normal renal function.
Because gabapentin does not bind to serum proteins and is not metabolized by the liver, it does not exhibit pharmacokinetic interactions with other antiepileptic drugs; its serum concentration is not changed following the addition or discontinuation of other common anticonvulsants (eg, phenobarbital, phenytoin, carbamazepine, valproic acid), nor is their serum concentration altered upon adding or discontinuing gabapentin.
Adverse effects are infrequent and usually resolve with continued treatment. The most common side effects include somnolence, dizziness, ataxia, and fatigue. Experience to date indicated that gabapentin is safe and relatively nontoxic.
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.
2.0-20.0 mcg/mL
Interpretation Provides information to assist in interpretation of the test results
Therapeutic ranges are based on specimens drawn at trough (ie, immediately before the next dose).
Most individuals display optimal response to gabapentin with serum levels of 2 to 20 mcg/mL. Some individuals may respond well outside of this range, or may display toxicity within the therapeutic range; thus, interpretation should include clinical evaluation. Some patients require high doses to achieve response, resulting in concentrations as high as 80 mcg/mL. Dosage reduction should be based on signs of toxicity, not the serum concentration.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test cannot be performed on whole blood. Serum must be separated from cells within 2 hours of draw. Specimens that are obtained from gel tubes are not acceptable.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Patsalos PN, Berry DJ, Bourgeois BF, et al: Antiepileptic drugs-best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia 2008;49(7):1239-1276
2. Johannessen SI, Tomson T: Pharmacokinetic variability of newer antiepileptic drugs: when is monitoring needed? Clin Pharmacokinetics 2006;45(11):1061-1075
Method Description Describes how the test is performed and provides a method-specific reference
Enzyme-multiplied immunoassay technique (EMIT) performed using Olympus analyzer. EMIT offers an alternative to the traditional spectroscopic and chromatographic method for quantitating blood concentrations of drugs. The technique for drugs is based upon an enzymatic assay for glucose-6-phosphate dehydrogenase, using spectral properties at 340 nm, in which the reduction of nicotinamide adenine dinucleotide (NAD) substrate is monitored. The basis of the drug detection technique is an immunological reaction between the drug and a specific antibody. The reagent contains the enzyme (glucose-6-phosphate dehydrogenase) to which the drug is covalently bound and antibody-specific to the drug. The antibody binds most of the drug-bound enzyme, rendering the enzyme inactive. This results in a baseline enzymatic activity. In the presence of free drug, antibody equilibrates between free drug and enzyme-bound drug leaving some of the drug-bound enzyme uncomplexed and able to catalyze the reaction. If more free drug is introduced, either as standard or sample, then competition for the antibody takes place between the drug in the sample and the drug attached to the enzyme. This results in more drug-bound enzyme being left uncomplexed and able to catalyze the enzyme reaction at a greater rate as compared to the baseline activity. The observed enzyme activity increases with the amount of total free drug in the sample.(Moyer TP: Therapeutic drug monitoring. In Tietz Textbook of Clinical Chemistry. Fourth edition. Edited by CA Burtis, ER Ashwood. WB Saunders Company, Philadelphia, 2005, pp 1237-1285)
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.
Monday through Sunday; Varies
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.
80299
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 |
|---|---|---|
| 80826 | Gabapentin, S | 9738-6 |
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