الفهرس 
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Abstract
Hemodialysis is the most prevalent modality of renal replacement therapy for patients with kidney failure, it is a technique that is used to achieve the extracorporeal removal of waste products such as urea and creatinine and excess water from the blood when the kidneys are in a state of renal failure. (Pends, et al., Pends, et al., Pends, et al., Pends, et al., Pends, et al., Pends, et al., Pends, et al., Pends, et al., 2007200720072007)
The major circulating form of vitamin D is 25(OH) D and it is the best measure of vitamin D status because it has a long half-life 2-3 weeks vs 4 hours for (1, 25 [OH] 2D), reproducible assay, high concentrations (100 times compared to 1, 25 [OH] 2D), and lack of fluctuations induced by PTH in response to subtle changes in serum calcium levels.( Hollis, Hollis, Hollis, Hollis, Hollis, Hollis, Hollis, et al., et al., et al., et al., et al., 2010201020102010)
The main function of vitamin D in its active form (calcitriol or 1, 25-dihydroxyvitamin D) is to maintain serum calcium and phosphorus levels, which are required for bone mineralization. Calcitriol functioning as part of the endocrine system for maintaining serum calcium levels, elevates plasma ionized calcium levels to the normal range .It has also additional roles in the regulation of the cardiovascular system, immune response, and nervous system, as well as proliferation and differentiation of cells.( Ross, et al., 2011)
Several epidemiologic studies have reported patients with CKD and ESRD treated by dialysis to have lower 25(OH) D concentrations.
A wide range of criteria are used to define vitamin D deficiency, and unfortunately, there is no consensus on this issue. Many clinicians define serum 25 (OH)D levels <20 ng/mL as deficient, 20-29.9 ng/mL as insufficient, and >30 ng/ml as sufficient there also is controversy regarding the upper limit of normal, with different cutoffs of 50-150 ng/mL proposed by different experts.( (Feldman , 2011)
Many factors may account for low levels of 25(OH) D in kidney disease, including the loss of vitamin D binding protein in the urine, ineffective synthesis in the skin upon exposure to ultraviolet B radiation, and likely reduced nutritional intake and sun exposure.( . (Laclair, et al., 2005).
Disturbances in mineral and bone metabolism are prevalent in chronic kidney disease (CKD) and are an important cause of morbidity, decreased quality of life, and extra skeletal calcification that have been associated with increased cardiovascular mortality. These disturbances have traditionally been termed renal osteodystrophy now this disturbance in mineral and bone metabolism accompanied by soft tissue and vascular calcification is referred to as CKD–mineral and bone disorder (CKD–MBD). (Moe, et al., 2006).
In this study, we tried to assess the level of 25(OH) vitamin D and its relation with calcium, phosphorus and parathyroid hormone.
This cross sectional study included seventy patients on maintenance HD were selected from dialysis unit of Elshohda hospital in Menoufia government, and twenty healthy subject with no chronic illness enrolled as control group, 25(OH) vitamin D estimated and individual who had 25(OH) vitamin D level ≤30 ng/ml were considered 25(OH) vitamin D deficient and individual who had 25(OH) vitamin D level >30 ng/ml are 25(OH)vitamin D sufficient.
All The patients were subjected to the following:
1. Clinical examination:
Through history taking and full clinical examinations
2. laboratory investigation:
A. Routine investigations:
- Complete blood count
- Serum calcium
- Serum phosphorus
- Serum albumin
- Parathyroid hormone level
B. Special investigation:
- Serum 25-hydroxyvitamin D was measured using an enzyme linked immune sorbent assay.