Diagnostic Testing and Laboratory Procedures
Specimens and Quality
Diagnostic testing depends on correct collection, handling, and documentation. Identify the patient, verify the order, prepare supplies, and label the specimen at the bedside in the patient’s presence. Know collection methods: venipuncture, capillary puncture, clean-catch urine, timed urine, and swabs. Fasting status and timing matter for glucose and lipid tests.
Concepts to Master
- Venipuncture order of draw for common tubes: blood cultures, light blue (coagulation), red or gold (serum), green (heparin), lavender (EDTA), gray (glucose/fluoride).
- Capillary puncture: warm the site, use the side of the fingertip, wipe away the first drop.
- Hemolysis prevention: avoid excessive tourniquet time, vigorous shaking, and small-bore needles.
- CLIA-waived tests: follow manufacturer instructions and perform quality controls.
- Reference ranges and critical values: report critical results immediately; do not interpret beyond scope.
Traps
Questions test order of draw, tourniquet time (generally under one minute), and labeling. An unlabeled or mislabeled specimen is rejected - never label it later away from the patient. Do not confuse capillary and venous collection, and do not shake tubes; invert them gently. A critical value is reported, not filed.
Worked Example
A lavender-top tube is drawn before a light blue tube. The coagulation result may be affected, so the specimen may need to be redrawn. Rule of thumb: “label at the bedside, fill tubes in order, and when in doubt, recollect rather than report an unreliable result.”