32 The majority of studies reviewed use this method to determine vitamin B6 status, with the exception Dabrafenib price of Mydlik and Descombes who use erythrocyte activity. This method has been criticized by some because of the shortened life span of red cells in chronic renal failure and the higher activities of some enzymes in younger erythrocytes.33 Some data, however, suggest that erythrocyte glutamic-oxaloacetic transaminase levels are more reliable than plasma or serum.9 Other information suggests pyridoxal may be a more reliable indicator of vitamin B6 metabolism as inorganic phosphate and alkaline phosphatase may interfere with plasma PLP measurements.34 While there is conflict, plasma

PLP is probably more readily available as a therapeutic guide.3 Differences in reference ranges for the classification of vitamin B6 status can, however, further cloud the picture of deficiency. While this review focuses on measures of vitamin status, dietary intake of vitamins has previously been shown to be low in the haemodialysis population.35 This is especially true of vitamin B6. While nutrient reference DNA Damage inhibitor values (NRV) have been determined from depletion/repletion studies, and are set for the Australian population at 1.5–1.7 mg/day,36 a recent US population-based study showed that vitamin B6 intakes between 3 and 4.9 mg/day would leave at risk

groups with inadequate vitamin status.32 US nutrition intake information in the haemodialysis population has shown that the mean intake is far less than these lower end recommendations, at 1.21 ± 0.39 mg/day.37 Australian data for the same population indicates intake levels are less again; 1.0 ± 0.3 mg/day in men and 0.6 ± 0.3 mg/day in women.38 More recent data show vitamin B6 intakes of 0.9 ± 0.37 mg/day in 67 haemodialysis patients.39 These data show suboptimal intake in this population, which is well below the NRV. In addition, foods high in vitamin B6, such as wheat bran, avocado, banana,

lentils, walnuts, soybean, potatoes, eggs, meat, fish, cheese and milk, are often limited in the haemodialysis population owing to their potassium and phosphate contents. As it is water soluble, Smoothened vitamin B6 is affected by the cooking process, which further diminishes availability.40 More recent nutrient intake data along side accurate dialysate PLP measures would provide further insight into current vitamin B6 status of the haemodialysis population. What does a deficiency in vitamin B6 mean for the haemodialysis population? Vitamin B6 is involved in many vital metabolic functions, and is important for the normal function of multiple organ systems. It is a cofactor for enzymes involved in the synthesis and catabolism of neurotransmitters, homocysteine trans-sulfuration and the metabolism of other amino acids, fats and glycogen. It also modulates the action of hormones and affects immune competence.