: 1441 Rai staging system (most commonly used in the United States) 
Stage 0: characterized by absolute lymphocytosis (>15,000/mm3) without lymphadenopathy, hepatosplenomegaly, anemia, or thrombocytopenia
Stage I: characterized by absolute lymphocytosis with lymphadenopathy without hepatosplenomegaly, anemia, or thrombocytopenia
Stage II: characterized by absolute lymphocytosis with either hepatomegaly or splenomegaly with or without lymphadenopathy
Stage III: characterized by absolute lymphocytosis and anemia (hemoglobin <11 g/dL) with or without lymphadenopathy, hepatomegaly, or splenomegaly
Stage IV: characterized by absolute lymphocytosis and thrombocytopenia (<100,000/mm3) with or without lymphadenopathy, hepatomegaly, splenomegaly, or anemiaBinet classification (most commonly used in Europe) 
Clinical stage A: characterized by no anemia or thrombocytopenia and fewer than three areas of lymphoid involvement (Rai stages 0, I, and II)
Clinical stage B: characterized by no anemia or thrombocytopenia with three or more areas of lymphoid involvement (Rai stages I and II)
Clinical stage C: characterized by anemia and/or thrombocytopenia regardless of the number of areas of lymphoid enlargement (Rai stages III and IV)

Array-based karyotyping
Array-based karyotyping is a cost-effective alternative to FISH for detecting chromosomal abnormalities in CLL. Several clinical validation studies have shown >95% concordance with the standard CLL FISH panel. Related diseases
In the past, cases with similar microscopic appearance in the blood but with a T cell phenotype were referred to as T-cell CLL. However, these are now recognized as a separate disease group and are currently classified as T-cell prolymphocytic leukemias (T-PLL).
Complications
Complications include a low level of antibodies in the bloodstream (hypogammaglobulinemia) leading to recurrent infection, warm autoimmune hemolytic anemia in 10–15% of patients, and bone marrow failure. Chronic lymphocytic leukemia may also transform into Richters syndrome, the development of fast-growing diffuse large B cell lymphoma, prolymphocytic leukemia, Hodgkins lymphoma, or acute leukemia in some patients. Its incidence is estimated to be around 5% in people with CLL.Gastrointestinal (GI) involvement can rarely occur with chronic lymphocytic leukemia. Some of the reported manifestations include intussusception, small intestinal bacterial contamination, colitis, and others. Usually, GI complications with CLL occur after Richter transformation. Two cases to date have been reported of GI involvement in chronic lymphocytic leukemia without Richters transformation. Cause
CLL can also be caused by a number of epigenetic changes, which are adaptations that add a tag to specific DNA sequences, rather than altering the sequence itself. In CLL, these changes can be classified into the addition of 3 different methyl subgroups (naïve B-cell-like, memory B-cell-like, and intermediate), which impact how much that DNA sequence is transcribed. Some relevant genetic mutations may be inherited. Since there is no one single mutation that is associated with CLL in all cases, an individual’s susceptibility may be impacted when multiple mutations that are associated with an increase in the risk of CLL are co-inherited. Up until 2020, 45 susceptibility loci have been identified. 93% of these loci are linked to the alteration of 30 gene expressions involved in immune response, cell survival, or Wnt signaling.