An elevated blood phosphate level (hyperphosphataemia) also indicates the presence of CKD, as the chronically damaged kidneys can excrete less phosphate. However, other factors can also influence phosphate levels, for instance the meat content of food and time of last meal. In addition, phosphate levels in young cats are always higher. In isolation, an elevated phosphate level is as inconclusive as an isolated elevated urea level. Only a combination of elevated creatinine, urea and phosphate blood levels indicates the presence of CKD.

Further tests, such as urine analyses, then need to be carried out for verification. In the context of CKD management, phosphate levels provide a good indication of whether phosphate-reduced therapy has been effective.

Phosphate concentrations should be below 1.9 mmol/l, otherwise an appropriate phosphate-reducing therapy should be undertaken. The normal phosphate range is approximately 0.8–1.9 mmol/l.

Blood phosphate should be below 1.9 mmol/l.