Chronic kidney disease (CKD) describes abnormal kidney function and/or structure. It is common and often exists together with other conditions, such as cardiovascular disease and diabetes.

The 'National service framework for renal services' adopted the US 'National Kidney Foundation kidney disease outcomes quality initiative' (NKF-KDOQI) classification of CKD. This classification divides CKD into 5 stages according to the extent of a person's loss of renal function. Stage 4 CKD is defined by a glomerular filtration rate (GFR) of 15–29 ml/min/1.73 m2, and stage 5 by a GFR of less than 15 ml/min/1.73 m2.

CKD progresses to these more advanced stages in a small, but significant percentage of people. In 2010, the Health Survey for England reported a prevalence of moderate to severe CKD (stages 3 to 5) of 6% in men and 7% in women, as a percentage of the total population in England. CKD stages 4 and 5 were reported at a prevalence of 1% or less. Although this figure might seem small, it translates to a prevalence of up to 520,000 people in England alone.

When CKD stage 5 advances to end-stage renal disease (ESRD), some people progress to renal replacement therapy (RRT). The UK Renal Registry reported that 49,080 adult patients were receiving RRT in the UK at the end of 2009. Of these, 25,796 were receiving RRT in the form of dialysis (a population sometimes classified CKD stage 5D).

As kidney dysfunction advances, there is a higher risk of mortality and some comorbidities become more severe. Hyperphosphataemia is one example of this, and occurs because of insufficient filtering of phosphate from the blood by poorly functioning kidneys. This means that a certain amount of the phosphate does not leave the body in the urine, instead remaining in the blood at abnormally elevated levels.

High serum phosphate levels can directly and indirectly increase parathyroid hormone secretion, leading to the development of secondary hyperparathyroidism. Left untreated, secondary hyperparathyroidism increases morbidity and mortality and may lead to renal bone disease, with people experiencing bone and muscular pain, increased incidence of fracture, abnormalities of bone and joint morphology, and vascular and soft tissue calcification.