HCL-V differs from classic HCL principally in these respects:

Higher white blood cell counts, sometimes exceeding 100,000 cells per microliter
A more aggressive course of disease requiring more frequent treatment
Hairy cells with an unusually large nucleolus for their size
Production of little excess fibronectin produced by classic hairy cells to interfere with bone marrow biopsies
Low or no cell-surface expression of CD25 (interleukin-2 [IL-2] receptor alpha chain, or p55).Low levels of CD25, a part of the receptor for a key immunoregulating hormone, may explain why HCL-V cases are generally much more resistant to treatment by immune-system hormones.HCL-V, which usually features a high proportion of hairy cells without a functional p53 tumor suppressor gene, is somewhat more likely to transform into a higher-grade malignancy. A typical transformation rate of 5-6% has been postulated in the UK, similar to the Richters transformation rate for splenic lymphoma with villous lymphocytes (SLVL) and CLL. Among HCL-V patients, the most aggressive cases normally have the least amount of p53 gene activity. Hairy cells without the p53 gene tend, over time, to displace the less aggressive p53(+) hairy cells. Some evidence suggests that a rearrangement of the immunoglobulin gene VH4-34, which is found in about 40% of HCL-V patients and 10% of classic HCL patients, may be a more important poor prognostic factor than variant status, with HCL-V patients without the VH4-34 rearrangement responding about as well as classic HCL patients. Hairy cell leukemia-Japanese variant
The variant called hairy cell leukemia-Japanese variant, or HCL-J, is more easily treated. Treatment with cladribine has been reported.
Hairy cells are visible in this test in about 85% of cases.Most patients require a bone-marrow biopsy for final diagnosis. The bone marrow biopsy is used both to confirm the presence of HCL and also the absence of any additional diseases, such as Splenic marginal zone lymphoma or B-cell prolymphocytic leukemia. The diagnosis can be confirmed by viewing the cells with a special stain known as TRAP (tartrate resistant acid phosphatase). More recently, DB44 testing assures more accurate results. Definitively diagnosing HCL is also possible through flow cytometry on blood or bone marrow. The hairy cells are larger than normal and positive for CD19, CD20, CD22, CD11c, CD25, CD103, and FMC7 antigens. (CD103, CD22, and CD11c are strongly expressed. )Hairy cell leukemia-variant (HCL-V), which shares some characteristics with B cell prolymphocytic leukemia (B-PLL), does not show CD25 (also called the interleukin-2 receptor, alpha). The differential diagnoses include several kinds of anemia, including myelophthisis and aplastic anemia, and most kinds of blood neoplasms, including hypoplastic myelodysplastic syndrome, atypical chronic lymphocytic leukemia, B-cell prolymphocytic leukemia, or idiopathic myelofibrosis. Classification
When not further specified, the "classic" form is often implied, but two variants have been described:  Hairy cell leukemia-variant and a Japanese variant. The non-Japanese variant is more difficult to treat than either classic HCL or the Japanese HCL. HCL-V
Hairy cell leukemia-variant (HCL-V) is usually described as a prolymphocytic variant of HCL. It was first formally described in 1980 by a paper from the University of Cambridges Hayhoe laboratory.