Unless the underlying cause is already apparent (and being appropriately managed), the presence of pancytopenia always warrants investigation by a hematologist, and the presence of severe pancytopenia (symptomatic anemia, WBC <500/mcL, and platelets <20x10^3/mcL) calls for urgent investigation (within 24-48 hours).
Flow diagram for evaluation of pancytopenia. Abbreviations: PNH, paroxysmal nocturnal hemoglobinuria; IBMFS, inherited bone marrow failure syndromes
From the collection of Jeff K. Davies
The causes of pancytopenia are diverse, and likely causes of pancytopenia differ in children and adults. Particular attention must be paid to patient and family history. Of significance is any history of previous pancytopenia, aplastic anemia, inherited bone marrow failure syndromes, early fetal loss, history of cancer, metabolic disorders, liver disease, or connective tissue disorders.
The most common cause of transient pancytopenia in all age groups is cytotoxic chemotherapy and radiotherapy. The symptoms and signs of pancytopenia relate to the blood cell lineages affected (RBCs, WBCs, and platelets). Mild pancytopenia is often symptomless and detected incidentally when a full blood count/CBC is performed for another reason. Spontaneous mucosal bleeding (gums, GI tract), petechiae, and purpura with easy bruising secondary to thrombocytopenia are usually the first symptoms to develop directly related to more severe pancytopenia. This is often followed by symptomatic anemia (fatigue, shortness of breath, dependent edema, chest pain in patients with ischemic disease) and bacterial infection secondary to neutropenia (fever, mucositis, abscesses, rigors).
A thorough physical exam is required, preferably by a hematologist. Weight loss and/or anorexia are harbingers of underlying infection (either precedent to the pancytopenia or as a result of it) and malignancy. Spontaneous mucosal bleeding (gums, GI tract), petechiae, and purpura with easy bruising secondary to thrombocytopenia are usually the first signs to develop directly related to more severe pancytopenia. These signs are often accompanied by lymphadenopathy (underlying infection, mononucleosis, lymphoproliferative disorder, and malignancy). Abdominal discomfort is a common presentation of splenomegaly and associated conditions. Widespread bone pain and loss of height suggest myeloma, joint pain systemic lupus erythematosus (SLE), and sore throat mononucleosis.
The following reference points to specific organ systems and associated conditions and is helpful to guide the examination.
Retinal hemorrhage (thrombocytopenia)
Leukemic infiltrates (acute leukemia)
Jaundiced sclera (paroxysmal nocturnal hemoglobinuria, hepatitis, cirrhosis)
Epiphora (dyskeratosis congenita)
Oral petechiae or hemorrhage (thrombocytopenia)
Stomatitis or cheilitis (neutropenia, vitamin B12 deficiency)
Gingival hyperplasia (leukemia)
Oral candidiasis or pharyngeal exudate (neutropenia, herpes family virus infections)
Tachycardia, edema, congestive cardiac failure (all signs of symptomatic anemia)
Evidence of prior cardiac surgery (cardiac disease associated with congenital syndromes)
Clubbing (lung cancer)
Tachypnea (sign of symptomatic anemia)
Right upper quadrant tenderness (hepatitis)
Lymphadenopathy (infection, lymphoproliferative disorder, HIV disease)
Signs of chronic liver disease
Splenomegaly (infection, myeloproliferative and lymphoproliferative disorders)
Malar rash (SLE)
Reticular pigmentation, dysplastic nails (dyskeratosis congenita)
Hyperpigmentation, café au lait (Fanconi anemia)
Short stature (Fanconi anemia, other congenital syndromes)
Abnormal thumbs (e.g., Fanconi anemia)
Signs associated with HIV disease
Morbilliform rash early
Kaposi sarcoma, ulcerating nodules later
Inherited bone marrow failure syndromes may have characteristic bony, renal, or pulmonary abnormalities. A search for these should not be part of an initial workup but, if found on images obtained for other reasons, should prompt further consideration of IBMFS as the etiology of pancytopenia.
A CBC and examination of peripheral blood film by a hematologist are essential. A standard battery of evaluative tests may include:
Serum reticulocyte count
Serum LFTs and hepatic serology
Serum coagulation profile, bleeding time, fibrinogen, and D-dimer
Serum direct antiglobulin test
Serum B12 and folate
Serum HIV and nucleic acid testing.
Specific testing pinpoints diagnosis in the following conditions:
Fanconi anemia: diepoxybutane (DEB) test for chromosomal breakage in peripheral blood lymphocytes
Lymphoproliferative disorders: immunophenotyping, cytogenetics, lymph node biopsy
Multiple myeloma: immunoelectrophoresis
Paroxysmal nocturnal hemoglobinuria (PNH): peripheral blood immunophenotyping for deficiency of phosphatidylinositol-glycan-linked molecules on peripheral blood cells (e.g., CD16, CD55, CD59)
CMV infection: serum IgM and IgG
Epstein-Barr: serum monospot, viral capsid antigen (VCA), and Epstein-Barr nuclear antibody (EBNA)
Leishmaniasis and other rare infections: blood and bone marrow culture, serum ELISA
Rare genetic and metabolic disease: leukocyte glucocerebrosides
Serum PSA in suspect cases of prostatic malignancy.
Examination of bone marrow is almost always indicated in cases of pancytopenia unless the cause is otherwise apparent (e.g., established liver disease with portal hypertension). The bone marrow exam consists of both an aspirate and a trephine biopsy, which yield complementary information in this setting. The differential diagnosis of pancytopenia may be broadly classified based on the bone marrow cellularity (reduced cellularity indicates decreased production of blood cells, whereas normal/increased cellularity indicates ineffective production or increased destruction or sequestration of blood cells).
Specifically, bone marrow aspirate permits examination of:
Cytology (megaloblastic change, dysplastic changes, abnormal cell infiltrates, hemophagocytosis, and infection [e.g., Leishman-Donovan bodies])
Immunophenotyping (acute and chronic leukemias, lymphoproliferative disorders)
Cytogenetics (myelodysplasia, acute and chronic leukemias, lymphoproliferative disorders).
Bone marrow trephine biopsy permits specific examination of cellularity:
Normal or increased in myelodysplasia, acute and chronic leukemia, myeloma with plasma cells, carcinomatus marrow infiltration, peripheral destruction/sequestration conditions, early HIV disease, and megaloblastic anemia
Decreased after chemotherapy, acute infection/sepsis, advanced HIV disease, hypoplastic myelodysplastic syndrome, congenital/inherited bone marrow failure syndromes, idiopathic aplastic anemia, systemic lupus erythematosus, and paroxysmal nocturnal hemoglobinuria.
Trephine biopsy also permits examination of histology and evaluation for:
Features of myelodysplasia (e.g., abnormal localization of immature precursors)
Reticulin stain (fibrosis).
In the developed world, it has been proposed that the most likely etiology of new onset pancytopenia, when investigated with bone marrow evaluation, is acute lymphoblastic leukemia in children and acute myeloid leukemia/myelodysplastic syndrome in adults.  In some other parts of the world, hypersplenism and infection are the most frequent etiologies of pancytopenia. 
Abdominal ultrasound scan or CT scan of the abdomen is indicated to evaluate for splenomegaly. CXR may reveal tumor masses responsible for pancytopenia (e.g., carcinoma, thymoma). In cases where metastatic infiltration of the bone marrow is suspected, thyroid ultrasound or breast imaging may also be appropriate. Inherited bone marrow failure syndromes may have characteristic bony, renal, or pulmonary abnormalities. A search for these should not be part of an initial workup but, if found on images obtained for other reasons, should prompt further consideration of IBMFS as the etiology of pancytopenia.