Which factor best explains the discrepancy between a high digoxin level and a normal clinical status?

Choosing the presence of an interfering substance that cross-reacted in the fluorescent immunoassay is the most logical explanation for the discrepancy between a high digoxin level and a normal clinical status. In clinical chemistry, immunoassays are used to measure drug levels, and they can sometimes produce false-positive results due to the influence of substances that are present in the sample.

These interfering substances might mimic the structure of the digoxin molecule or bind to the antibodies used in the assay, leading to an artificially elevated readout that does not accurately reflect the true physiological level of digoxin in the patient's system. Consequently, the patient may exhibit normal clinical signs despite the high levels indicated by the assay.

This scenario underlines the importance of interpreting laboratory results in the context of clinical symptoms and the possibility of assay interference. It highlights why confirmatory testing or different methodologies may be necessary to verify results, particularly in cases where clinical presentation does not align with laboratory findings.