Plasma oxalate and glycolate levels in patients with chronic kidney disease (CKD stage 4 and 5).

Oxalate is a metabolic end product of glyoxylate metabolism. It is produced by
the liver and excreted in the urine. Once renal failure develops, patients are
unable to excrete oxalate in the urine, which leads to a rise in plasma oxalate
levels. Until now, normal values of plasma oxalate levels in patients with
end-stage renal disease (ESRD) have not been established. The lack of reference
values complicates the interpretation of the increased values found in ESRD
patients. This is particularly relevant in patients with renal failure due to
hyperoxularia, in whom elevated plasma oxalate levels can be ascribed both to
the primary disease and the loss of kidney function. Primary Hyperoxaluria (PH)
is a rare autosomal disease in which hepatic overproduction of oxalate (and
glycolate) occurs. Secondary causes of hyperoxaluria include intestinal oxalate
hyperabsorption and excessive dietary intake of oxalate. In both, the level of
plasma oxalate influences therapeutic decision-making.

The aim of this study is to establish reference values for plasma oxalate and
plasma glycolate levels in patients with chronic kidney insufficiency. Values
in patients with PH and secondary hyperoxaluria will be compared to values
measured in patients on renal replacement therapy (RRT) in our centre and
patients with pre-terminal renal insufficiency.

This is a cross-sectional, observational study. Plasma samples will be obtained
from patients with pre-terminal renal insufficiency during regular outpatient
visits and from patients on renal replacement therapy (RRT) both prior to and
after regular hemodialysis or peritoneal dialysis treatments.

There is no additional risk or burden associated with participation. Patients
with pre-terminal renal insufficiency will undergo blood sampling for plasma
oxalate and glycolate levels during regular outpatient clinic visits. Blood
will be drawn prior to dialysis for patients on RRT.