10	P. Imbach

•The serum potassium level may be low in patients with malnutrition or renal tubular loss

•Serum hypocalcemia may occur in patients with renal insufficiency or due to calcium binding to phosphate released by leukemic cells. Symptoms: hyperventilation, nausea, confusion, carpopedal spasms, convulsions, nausea, vomiting

•Serum hypercalcemia in patients with marked leukemic bone infiltration

•Abnormal liver function may be due to liver infiltration by leukemic cells or as a side effect of treatment. Increased level of transaminases with/without hyperbilirubinemia in patients with hepatomegaly. Differential diagnosis: viral hepatitis

•Serum immunoglobulin levels: In 20% of children with ALL, low serum IgG and IgM levels can be present

2.3.4Bone Marrow Analysis

•Bone marrow analysis serves to characterize the blast cells and to determine the degree of reduction of normal erythro-, myelo-, and thrombopoiesis, as well as about hyperor hypocellularity

•Morphological, immunological, biochemical, and cytogenetic analyses are required

•Differential diagnosis: aplastic anemia and myelodysplastic syndrome

•Usually the marrow is hypercellular with uniform morphology; megakaryocytes are usually absent

2.4Leukemic Cell Characterization and Classification

2.4.1Morphology

•Leukemic cells are characterized by a lack of differentiation, by a nucleus with diffuse chromatin structure, with one or more nucleoli, and by basophilic cytoplasm

•Differentiation between myeloid and lymphoid cells may be difficult. Criteria include:

–Cell size: larger in myeloblasts

–Chromatin structure of nucleus: heterogeneous in myeloblasts, homogeneous/ and/or fine in lymphoblasts

–Nucleoli: at least two in myeloblasts

–Ratio between nucleus and cytoplasm: markedly higher in lymphoblasts

–Cytoplasm: in lymphoblasts, blue and usually homogeneous (sometimes with vacuoles); in myeloblasts, granular, and sometimes with Auer rods, particularly in acute promyelocytic leukemia

–The French-American-British classification was in use for many years and is now substituted by the WHO classification: see WHO publication center, lymphoid tissue. For microscopy reason the FAB classification is presented here

2 Acute Lymphoblastic Leukemia	11

French-American-British (FAB) classification of lymphoblasts

L1: 85% of children with ALL

•Cell size: small cells predominate

•Nuclear chromatin: usually homogeneous

•Nuclear shape: oval, almost fills cell

•Nucleoli: Normal; occasionally clefted or indented

•Cytoplasm: Scanty

•Basophilia of cytoplasm: very few

•Cytoplasmic vacuolation: variable

L2: 14% of children with ALL

•Cell size: Variable in size

•Nuclear chromatin: variable, heterogeneous

•Nuclear shape: irregular clefting, indentation common

•Nucleoli: one or more present; often large

•Cytoplasm: variable, often moderately abundant

•Basophilia of cytoplasm: variable, sometimes deep

•Cytoplasmic vacuolation: variable

L3: 1% of children with ALL

•Cell size: Large homogeneous cells

•Nuclear chromatin: finely stippled and homogeneous

•Nuclear shape: normal, i.e., oval to round

•Nucleoli: prominent, one or more

•Cytoplasm: moderately abundant

•Basophilia of cytoplasm: very deep

•Cytoplasmic vacuolation: often prominent

2.4.2Cytochemistry

•Peroxidase: positive results in myeloblasts with cytoplasmic granules

•Esterase (a-naphthyl acetate esterase, ANAE): used in identification of monoor histiocytic elements

•Leukocyte alkaline phosphatase: low or no activity in granulocytes of CML

•Periodic acid Schiff (PAS): most circulating leukocytes are PAS-positive. PAS is strongly positive in lymphoblasts, especially in T-cell lymphoblasts

•Sudan black is usually positive in myeloid cells/especially immature cells

Cytochemical reactions
	Lymphoblasts	Myeloblasts
Peroxidase	−	+
Sudan black	−	+
Periodic acid-Schiff	++	±
Esterase	−	±b
Terminal deoxynucleotidyl	+a	−
transferase: TdT
aOften negative in L3 morphology

bAlso may be positive in acute monocytic leukemia