Serum

Preferred Minimum: 1.5 mL serum
Absolute Minimum: 1.0 mL serum

Severely lipemic, or hemolyzed specimens.

6 days upon receipt at reference laboratory

< or = 0.02 nmol/L

Useful for confirming the diagnosis of myasthenia gravis (MG), distinguishing acquired disease (90% positive) from congenital disease (negative), detecting subclinical MG in patients with thymoma or graft- versus-host disease, monitoring disease progression in MG or response too immunotherapy, an adjunct to the test for P/Q-type calcium channel binding antibodies as a diagnostic aid for Lambert-Eaton myasthenic syndrome (LES) or primary lung carcinoma.

Positive results for muscle acetylcholine receptor (AChR) binding or striational antibodies are found in 13% of patients with Lambert-Eaton myasthenic syndrome (LES). This does not mean that myasthenia gravis (MG) and LES co-exist. Antibodies to P/Q type calcium channels are found in 95% of LES patients, but not in MG, except in very rare paraneoplastic cases related to small-cell lung carcinoma. Positive results are frequently found with autoimmune liver disease. Magnitude of the result is not useful for predicting severity of MG. This test should not be requested in patients who have recently received radioisotopes, therapeutically or diagnostically, because of potential assay interference. The specific waiting period before specimen collection will depend on the isotope administered, the dose given and the clearance rate in the individual patient. Specimens will be screened for radioactivity prior to analysis. Radioactive specimens received in the laboratory will be held 1 week and assayed if sufficiently decayed, or canceled if radioactivity remains.

Radioimmunoassay (RIA)

83519