Why Lavender (EDTA) Tubes Are Unsuitable for CBC: Correct Tube Selection
No. Lavender-top tubes contain EDTA (K2 or K3), which chelates calcium and preserves cellular morphology for hematology — they ARE the standard tube for CBC.
Correction: The original statement is incorrect. Light blue (sodium citrate) tubes are for coagulation studies (PT/INR, aPTT), not CBC. Sodium citrate dilutes blood 1:9, altering cell concentrations and invalidating CBC indices.
Correct Tube Usage
| Tube Color | Additive | Primary Use |
|---|---|---|
| Lavender / Purple | EDTA (K2/K3) | CBC, HbA1c, blood type, lead level |
| Light Blue | Sodium Citrate (3.2% or 3.8%) | Coagulation: PT/INR, aPTT, fibrinogen, D-dimer |
| Red / Gold (SST) | Clot activator ± gel | Chemistry, serology, immunology |
| Green | Heparin (Li/Na/NH4) | Plasma chemistry, stat electrolytes, ammonia |
| Gray | Fluoride/Oxalate | Glucose, lactate, alcohol |
Always follow your laboratory's specific collection guidelines. Order of draw matters to prevent additive carryover.
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