Fasting for WBC Count: Not Required — Clarifying Pre-Test Instructions

A white blood cell (WBC) count as part of a complete blood count (CBC) does not require fasting. You may eat and drink normally unless your clinician orders additional tests that do require fasting (e.g., glucose, lipids).

Tests Requiring Fasting (8–12 hours, water only)

• Fasting glucose
• Lipid panel (traditional; non-fasting increasingly accepted for screening)
• Iron studies (prefer morning fasting)
• Insulin, C-peptide, homocysteine
• Certain hormone panels

Tests NOT Requiring Fasting

• CBC (WBC, RBC, Hb, Hct, platelets)
• Basic/Comprehensive metabolic panel (BMP/CMP)
• TSH, free T4
• HbA1c
• Coagulation studies (PT/INR, aPTT)
• Most infectious serologies

Best Practices

• Confirm requirements with ordering office — lab policies vary.
• Hydrate well (eases venipuncture).
• Avoid strenuous exercise before CBC (transient leukocytosis).
• Inform phlebotomist of medications (e.g., heparin, chemo).

If only CBC/WBC is ordered: no fasting needed. Schedule conveniently.