Equimolar ammonia interference in potassium measurement on the Osmetech OPTI CCA: a reply.

gate collection tubes from various manufacturers, available evidence, including our data, indicates that these problems may be common. The more rapid coagulation process in clot-activator tubes may be associated with more extensive proteolysis in the specimen, potentially leading to greater protein fragmentation that is subsequently detected by mass spectrometry. Nonbiological changes, observed repeatedly in the low-molecular-weight serum proteome profiles, raise the question of whether serum is the specimen of choice for major proteinand/or peptide-type clinical analytes such as hormones and tumor markers (8 ). In summary, clot activator-containing collection tubes may lead to preanalytical artifacts in proteomic studies. In our experience, these tubes can be effectively substituted with Li-heparin plasma tubes for chemistry analytes or plain serum tubes used for immunoassay and specimen banking.