What are the pre-analytical, pre-collection, collection, and post-collection variables affecting laboratory results, and what is the proper drawing order for collection tubes?

Here are the answers to questions 5, 6, and 7:

5. Preanalytical, Pre-collection, Collection, and Post-collection Variables Affecting Laboratory Results

• Pre-analytical variables (before collection): Patient preparation (e.g., fasting status, medication, exercise, posture), time of day for collection.
• Pre-collection variables (during collection setup): Incorrect selection of collection tubes, use of expired tubes, improper labeling materials.
• Collection variables (during collection): Incorrect venipuncture technique (e.g., prolonged tourniquet application, vigorous mixing, hemolysis), incorrect order of draw, insufficient sample volume (QNS).
• Post-collection variables (after collection, before analysis): Improper mixing of tubes, delayed transport to the lab, incorrect storage temperature, exposure to light, errors during centrifugation, delayed separation of serum/plasma from cells.

6. Proper Drawing Order for Collection Tubes

The standard order of draw is crucial to prevent cross-contamination of additives:

1. Blood Culture (Sterile tube, typically yellow top)
2. Coagulation Tube (Sodium Citrate, light blue top)
3. Serum Tube (with or without clot activator, with or without gel separator; red, gold, or tiger top)
4. Heparin Tube (Lithium, Sodium, or Ammonium Heparin; green top)
5. EDTA Tube (K2EDTA or K3EDTA; lavender/purple top)
6. Glycolytic Inhibitor Tube (Sodium Fluoride/Potassium Oxalate; gray top)

7. General Steps for Processing Samples

1. Reception and Accessioning: Samples are received, patient and sample information is verified, and a unique laboratory identification number is assigned.
2. Centrifugation: If serum or plasma is required, blood samples are spun to separate cellular components from the fluid portion.
3. Aliquotting: The separated serum, plasma, or other fluid is transferred into smaller, labeled tubes for specific tests or storage.
4. Storage: Samples are stored under appropriate conditions (e.g., refrigerated, frozen, room temperature, protected from light) until testing or archiving.
5. Distribution: Aliquoted samples are distributed to the relevant laboratory sections for analysis.
6. Disposal: Remaining sample material and used collection tubes are properly disposed of after testing and retention periods.