GABA-B-Receptor Antibody by CBA, Serum
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:
-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
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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.
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.
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.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
A negative result does not exclude autoimmune encephalopathy or cancer.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
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