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.
Treatment of the lymphocytic group of cicatricial alopecias (including lichen planopilaris, frontal fibrosing alopecia, central centrifugal alopecia, and pseudopelade (Brocq) involves use of anti-inflammatory medications. The goal of treatment is to decrease or eliminate the lymphocytic inflammatory cells that are attacking and destroying the hair follicle. Oral medications may include hydroxychloroquine, doxycycline, mycophenolate mofetil, cyclosporine, or corticosteroids. Topical medications may include corticosteroids, tacrolimus,  pimecrolimus, or Derma-Smoothe/FS scalp oil. Triamcinolone acetonide, a corticosteroid, may be injected into inflamed, symptomatic areas of the scalp. Treatment of the neutrophilic group of cicatricial alopecias (folliculitis decalvans, tufted folliculitis) is directed at eliminating the predominant pathogenic microbes that are invariably involved in the inflammatory process. Oral antibiotics are the mainstay of therapy, and topical antibiotics may be used to supplement the oral antibiotics. In dissecting cellulitis, pathogenic microbes are not usually present. Isotretinoin in small doses may be helpful in treating dissecting cellulitis.Treatment of the mixed group of cicatricial alopecias (folliculitis keloidalis) may include antimicrobials, isotretinoin, and anti-inflammatory medications. Patients are recommended to discuss any treatment with a dermatologist, who also explains potential side effects, as well as laboratory tests that are needed before starting treatment and sometimes are monitored during treatment. The course of cicatricial alopecia is usually prolonged. Treatment is continued until the symptoms and signs of scalp inflammation are controlled, and progression of the condition has been slowed.