Therapeutic: <2.1 ng/mL at 6 hours after dose in adults. Critical value: >2.1 ng/mL (adults)

Digibind (fab fragment) interferes with digoxin assay. Call lab for details.

The assay is unaffected by icterus (bilirubin is less than 65 mg/dL), hemolysis (Hb is less than 100 mg/dL), lipemia (Intralipid is less than 1500 mg/dL), and biotin is less than 100 ng/mL (criterion: recovery within plus or minus 0.15 ng/mL at digoxin is less than 1.5 ng/mL, or within plus or minus 10% at digoxin levels is greater than 1.5 ng/mL). No interference was observed from rheumatoid factor (RF is less than 1630 IU/mL). In patients receiving therapy with high biotin doses (i.e. is greater than 5 mg/day) no sample should be taken until at least 8 hours after the last biotin administration. In vitro tests were performed on 69 commonly used pharmaceuticals. No interference with the assay was found. Digoxin-like immunoreactive substances (DLIS) have been identified in blood from patients in renal failure, liver failure, and pregnant women in their third trimester. Studies have shown that the presence of DLIS in a sample can result in a false elevation of digoxin when assayed by commercially available immunoassay.(1-3) The manufacturer of Digoxin Immune FAb (antibody fragment therapy) has stated that no immunoassay technique is suitable for quantitating digoxin in serum from patients undergoing this treatment.(4) Uzara and Nabumetone may cause falsely elevated digoxin results. As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposes. Digoxin contains additives which minimize these effects. In rare cases, interference due to extremely high titers of antibodies of streptavidin can occur. (1) Keys PW, Stafford RW. In: Taylor WJ, Finn AL, eds. Individualizing Drug Therapy: Practical Applications of Drug Monitoring. New York, Gross, Townsend, Frank, Inc; 1981;vol 3:1-21. (2) Valdes R Jr.: Clin Chem. 1985;31:1525-1532 (3) Valdiva R, Hornig Y, Gross S, Khayam-Bashi H: Digoxin-like Immunoreactive Factor Cross-reactivity in the CEDIA Digoxin R Assay on the RA-1000. Clin. Chem. 1990;36(6):1111 (4) Digibind Product Information. Burroughs Wellcome Co. Research Triangle Park. NC 1990