Can SIBO affect blood cell counts? RBC and/or WBC?

Be careful. "Small intestinal bacterial overgrowth" is usually a "pop", non-evidence-based diagnosis made by "independent medical thinkers." It's blamed for everything from rosacea to fibromyalgia, and you'll be offered a host of remedies but will never be "cured". If you haven't had a jejunal aspirate with a large number of bacteria to establish it, consider it unproven and seek evidence-based diagnosis/Rx.