Method, specimen, and drug-specific limits

For serious MRSA bloodstream infection with MIC 1 mg/L by broth microdilution, the stated AUC24/MIC target is 400–600 mg·h/L. This target is indication- and MIC-specific, not a target for every vancomycin use.

For conventional gentamicin, peak and trough timing follows the laboratory’s selected local protocol; about 30 minutes after infusion completion and within 30 minutes before the next dose are protocol-specific illustrations. Extended-interval dosing uses one random level at the time specified by the selected local nomogram; 6–14 hours after the first dose is a protocol-specific illustration. Digoxin is preferably a trough or at least six to eight hours after dose because earlier collection captures distribution.

Immunoassays can cross-react with metabolites or endogenous substances. Tacrolimus immunoassay and LC-MS/MS results are not interchangeable, and serial results should state and preferably retain the method. Digoxin-like immunoreactive substances and digoxin immune Fab can make routine immunoassay interpretation unreliable.

Use a direct free phenytoin concentration when protein binding is abnormal when available. The Sheiner-Tozer correction is an approximation and is less reliable in critical illness, severe renal failure, or marked hypoalbuminemia. Specimen suitability is measurand-specific, so a clotted, hemolyzed, short filled, or wrong-additive specimen requires the local acceptance rule for that test.

Declare the method and collection conditions that limit comparability.