Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

GABCC
61515
GABA
80826
Interpretation: GABA-B-receptor IgG is a valuable serological marker of autoimmune
encephalopathy and of a patient's immune response to cancer (usually small-cell carcinoma). This
autoantibody is usually accompanied by subacute neurological symptoms and signs, and is not found in
healthy subjects.
Reference Values:
Negative
Clinical References: 1. Lancaster E, Lai M, Peng X, et al: Antibodies to the GABA(B) receptor in
limbic encephalitis with seizures: case series and characterisation of the antigen. Lancet Neurol
2010;9(1):67-76 2. Boronat A, Sabater L, Saiz A, et al: GABA(B) receptor antibodies in limbic
encephalitis and anti-GAD-associated neurologic disorders. Neurology 2011;76(9):795-800
GABA-B-Receptor Antibody by CBA, Spinal Fluid
Clinical Information: Antibody targeting extracellular domains of the B1 subunit of the
GABA-B-receptor has been reported in patients with small-cell carcinoma-related autoimmune limbic
encephalitis, usually with prominent seizures. Seven of the initially reported 15 patients had 1 or more
coexisting antibodies documented in serum: N type calcium channel antibody, 3; GAD65 antibody, 3;
thyroid antibodies, 3; AGNA/SOX 1 antibody, 1. A subsequent study reported detecting
GABA-B-receptor antibody in the serum of 10 of 70 patients with limbic encephalitis (14%). Testing of
cerebrospinal fluid may be helpful when serum testing is negative.
Useful For: Evaluating new onset encephalopathy encompassing 1 or more of the following:
confusional states, psychosis, delirium, memory loss, hallucinations, seizures, dyssomnias, coma,
dysautonomias, or hypoventilation The following accompaniments should prompt suspicion for
autoimmune encephalopathy: -Headache -Autoimmune stigmata (personal or family history, or signs of
diabetes mellitus, thyroid disorder, vitiligo, poliosis [premature graying], myasthenia gravis, rheumatoid
arthritis, systemic lupus erythematosus) -History of cancer -Smoking history (20+ pack years) or other
cancer risk factors -Inflammatory cerebrospinal fluid or isolated protein elevation -Neuroimaging signs
suggesting inflammation Evaluating limbic encephalitis Directing a focused search for cancer
Investigating encephalopathy appearing in the course or wake of cancer therapy, and not explainable by
metastasis or drug effect
Interpretation: GABA-B-receptor IgG is a valuable serological marker of autoimmune
encephalopathy and of a patient's immune response to cancer (usually small-cell carcinoma). This
autoantibody is usually accompanied by subacute neurological symptoms and signs, and is not found in
healthy subjects.
Reference Values:
Negative
Clinical References: 1. Lancaster E, Lai M, Peng X, et al: Antibodies to the GABA(B) receptor in
limbic encephalitis with seizures: case series and characterisation of the antigen. Lancet Neurol
2010;9(1):67-76 2. Boronat A, Sabater L, Saiz A, et al: GABA(B) receptor antibodies in limbic
encephalitis and anti-GAD-associated neurologic disorders. Neurology 2011;76(9):795-800
Gabapentin, Serum
Clinical Information: 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
Current as of January 3, 2013 2:22 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 786