Chapter 29: Patient Sample Collection and Use of the Laboratory

Patient Sample Collection and Use of the Laboratory underscores the critical necessity of accurate patient identification and the legal and clinical hazards of mislabeling specimens. Detailed attention is given to various extra-laboratory factors that can skew biochemical data, including patient variables such as fasting status, physical posture, and the timing of pharmaceutical administration. The text provides a comprehensive analysis of venepuncture techniques, explaining how prolonged venous stasis can artificially elevate protein and calcium concentrations due to fluid shifts. Furthermore, it highlights common collection errors, such as "drip arm" contamination from intravenous infusions and the incorrect selection of anticoagulants—specifically noting how EDTA can chelate calcium and falsely raise potassium levels. The chapter also addresses the physiological and chemical changes that occur post-collection, such as in vitro haemolysis and delayed plasma separation, which frequently lead to pseudohyperkalaemia as intracellular ions leak from erythrocytes. Finally, it outlines standardized protocols for timed urine and faecal collections, stressing that effective communication between clinicians and laboratory staff is essential for interpreting anomalous results and managing urgent diagnostic requests.