Chan Su is a Chinese medicine prepared from the skin gland of a Chinese toad and is used in treating
arrhythmia and other
heart diseases. Danshen is prepared from the Chinese medicinal plant and is used for various
cardiovascular diseases including
angina pectoris. The authors studied the potential interference of such medicines with the widely used EMIT 2000 (Dade Behring; Deerpark, IL)
digoxin assay and the recently marketed
Randox digoxin assay (
Randox Laboratories Ltd, Antrim, United Kingdom) (both run on the Bayer ADVIA 1650 analyzer) (Bayer Diagnostics, Tarrytown, NY) and compared their results with an FPIA (Abbott Laboratories) and a chemiluminescent immunoassay (CLIA; Bayer Diagnostics) for
digoxin. Aliquots of
drug-free serum were supplemented with 1 microL
ethyl acetate extract of Danshen or aqueous extract of
Chan Su, and apparent
digoxin concentrations were measured by all four
digoxin immunoassays (FPIA, EMIT,
Randox, CLIA). The authors also supplemented aliquots of several different serum pools prepared from patients taking
digoxin with very small amounts of
Chan Su or
Danshen extract and compared
digoxin values with the control
digoxin values (serum pool containing no Chinese medicine). The authors observed no interference of Danshen in either EMIT,
Randox, or CLIA assay but observed an interference with the FPIA assay. On the other hand, the authors observed high interference of
Chan Su in the FPIA assay but moderate interference with the EMIT 2000 and
Randox digoxin assays. CLIA assay was again free from any interference. The authors also observed a wide variation in
digoxin-like immunoreactivity and magnitude of interference in
digoxin immunoassay in different brands of
Chan Su and Danshen, indicating poor quality control in manufacturing of these Chinese medicines. Taking advantage of the high protein binding of
digoxin-like immunoreactive components of
Chan Su, the authors further demonstrated that interference of
Chan Su in EMIT 2000 and
Randox assays can be mostly eliminated by monitoring free
digoxin.