Is a reduction in all the components of blood. So there are decreased red blood cells, white blood cells, and platelets (anaemia, neutropenia and thrombocytopenia). 

Red blood cells: Hb <12g/dL for women and <13.5g/dL for men
White blood cells (neutrophils): ANA <1500 
Platelets: <150x10^9/L 

There are many causes of pancytopenia, including leukaemia, aplastic anaemia, SLE, familial haemophagocytic syndrome, myelodysplastic syndrome, pernicious anaemia, among several others (consult your local wiki for further information). 

Schematic depiction of the Fanconi anemia DNA repair pathway. DNA damage activates the complex of Fanconi anemia−associated proteins FANCA, FANCB, FANCE, FANCF, FANCG and FANCL. FANCL is a ubiquitin ligase that probably causes the ubiquitination of FANCD2. This protein, together with another Fanconi anemia−associated protein, BRCA2 and RAD51, is involved in the repair of DNA damage. Nature Genetics  36, 1142 - 1143 (2004)

Fanconi Anemia, in three unforgettable words:

  1. Defective DNA repair that lead to various congenital anomalies: café-au-lait spots, short stature, radial and/or thumb malformations, genitourinary abnormalities, cardiopulmonary and gastrointestinal abnormalities.
  2. Pancytopenia. Signs and symptoms of pancytopenia include petechiae and easy bruising due to thrombocytopenia, pallor and fatigue due to anemia, and recurrent infections due to leukopenia.
  3. Cancer. A greatly increased risk (up to 4000 times) for developing hematologic and solid malignancies.

Pancytopenia and Fever – Basics, Clinical Manifestations, Diagnosis, Treatment

Basics DEFINITION Pancytopenia is deficiency of all cell elements of the blood. Leukopenia is usually defined as <5,000 leukocytes per milliliter. Anemia and thrombocytopenia are less well defined. Thrombocytopenia with 50,000 to 100,000 platelets per milliliter is usually considered…
Pancytopenia and Fever – Basics, Clinical Manifestations, Diagnosis, Treatment

Causes of Pancytopenia
  1. Aplastic anaemia
  2. Pernicious anaemia
  3. Systemic lupus erythematosus
  4. Myelodysplastic syndrome
  5. Severe folate / B12 deficiency
  6. Viral infections (HIV most common cause)
  7. Hypersplenism
  8. Gaucher’s disease
  9. Leukemia
  10. Medication
  11. Osteopetrosis
  12. Chronic radiation sickness
  13. Paroxysmal nocturnal haemoglobinuria