Specimen loading and aspiration

In most situations, the specimen presented to an automated analyzer is serum or plasma. Many state-of-the-art analyzers (e.g., CX/LX series, ADVIA 1650 and 2400, Architect c-8000 series, MODULAR, DIMENSION) directly sample serum from primary collection tubes of various sizes. With such analyzers, the collecting tubes most frequently used contain a separator material that forms a barrier between supernatant and cells (see Chapter 2), Some analyzers also sample from a cup or tube that is filled with serum transferred from the original specimen tube. 

Evaporation of specimen from cups or tubes in the loading zone has caused analytical errors as great as 50% over 4 hours.Operationally, all cups or tubes containing solution for analysis should be covered until the time the specimen is to be analyzed. Many manufacturers of automated analyzers provide covers for individual cups or for part or the whole of the loading zone to reduce losses caused by evaporation. Cups may be covered by Parafilm or by caps that are placed over the cups and that have crosscuts to permit ready entry of a specimen probe. A type of antievap-orative cover that reduces evaporative losses to less than 0.1%/hr has been described.  

---