Lab info below is from Dr Kaslow. I would add that I had severe vitamin B12 deficiency with normal MCV - called masked megaloblastic anaemia.
"The number of red blood cells is decreased in:
Iron deficiency (should see a low MCV)
Vitamin B6, B12, and/or Folic Acid deficiency (should see a high MCV )
Chronic Disease (Liver dysfunction (liver function tests might show abnormalities, kidney dysfunction (chemistry tests and the BUN, creatinine may be abnormal).
Free radical pathology.
Platelets are often decreased in:
Marrow depression (aplastic anemia, radiation, chemotherapy, drugs)
Marrow infiltration (acute leukemia, carcinoma, myelofibrosis, multiple myeloma)
Megaloblastic anemia (B12 and/or folic acid deficiency)
Immunologic (ITP, infectious mononucleosis (EBV), SLE, Lymphoma, CLL)
Drugs (chemotherapy, heparin)
Dilution due to overhydration
Coagulation disorders ( DIC, septicemia, hemolytic-uremic syndrome, TTP, large hemangiomas, heart valve, eclampsia)
Platelet aggregation or large platelets
Liver dysfunction (cirrhosis).
Idiopathic Cytopenic Purpura (ITP), a condition possibly related to viral infection, autoimmunity or chemical toxin.
Causes of Decreased WBC
Influenza (early stages)
Vitamin and mineral deficiencies"