Pathophysiology
Clinical meaning
Accurate specimen collection is fundamental to reliable diagnostic testing and appropriate clinical decision-making. Pre-analytical errors (specimen collection, handling, and transport) account for 60-70% of all laboratory errors. Key principles: (1) Patient identification โ verify two patient identifiers before every collection (full name + date of birth or medical record number). (2) Timing โ some specimens require specific timing: fasting glucose (8-12 hours NPO), trough drug levels (just before next dose), peak drug levels (30-60 minutes after IV, 1-2 hours after PO), cortisol (AM specimen, diurnal variation). (3) Technique โ proper collection prevents contamination: clean-catch midstream urine reduces bacterial contamination; blood cultures require aseptic technique (skin antisepsis with chlorhexidine, two sets from separate sites before antibiotics). (4) Order of draw for blood tubes (to prevent additive cross-contamination): blood culture bottles โ light blue (citrate/coagulation) โ red (serum/chemistry) โ green (heparin) โ lavender (EDTA/CBC) โ gray (fluoride-oxalate/glucose). (5) Labeling โ label at the bedside immediately after collection with patient identifiers, date, time, collector initials, and specimen type.