Validation Testing for Plasma Oxalate Levels in the Biochemical Laboratory at the Galilee Medical Center, in Collaboration With the Biochemistry Laboratory at CHARITE Hospital in Berlin, and Testing the Relationship Between Oxalate Levels and Vitamin C Levels in Plasma

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Background: Elevated plasma oxalate levels in various conditions, including: primary hyperoxaluria due to increased production in the liver, renal failure due to decreased renal excretion, intestinal diseases with fatty diarrhea due to increased intestinal absorption, and increased intake of substances containing oxalate or sources of oxalate. Primary hyperoxaluria type 1 is a rare hereditary disease in which there is an increase in oxalate production in the liver due to a defect in the AGT enzyme in the oxalate metabolism pathway. The disease causes end-stage renal failure, and until recently, the only treatment was liver and kidney transplantation. The disease is more common in our region, and the Pediatric Nephrology Unit is a center of expertise for this disease. In 2022, a new treatment for hyperoxaluria type 1, which is an alternative to liver transplantation (Lomecirane), was added to the health basket. With the introduction of this treatment in Israel, there was a need to test the level of oxalate in plasma in order to monitor the response to treatment and as part of the preparation for kidney transplantation in cases of type 1 hyperoxaluria with end-stage renal failure. There is no laboratory in Israel that performs plasma oxalate testing. The biochemistry laboratory at the Galilee Medical Center performs oxalate testing in urine using an enzymatic method. Testing for oxalate in plasma using this method requires external validation because the manufacturer intends this test for urine only. There are laboratories around the world that use this method to measure oxalate in plasma. Vitamin C is a precursor (source) for oxalate in the body. High vitamin C levels in dialysis may lead to increased oxalate, which is associated with worsening kidney damage and damage to other organs, including an increase in the incidence of cardiovascular disease. Dialysis patients are therefore advised to avoid vitamin C supplements. On the other hand, cases of symptomatic vitamin C deficiency in dialysis patients have been described due to their tendency to have an inadequate diet. One case was described in the literature by the Nephrology Department at our institution. Objectives: 1. To validate the plasma oxalate test by comparing it to an external laboratory that performs the test. 2. To examine the relationship between vitamin C levels and plasma oxalate levels in patients with varying degrees of renal failure. Importance: 1. Establishment of a laboratory service that does not currently exist in Israel and is clinically important for treatment decisions. 2. Assessing the relationship between vitamin C levels and oxalate levels in renal failure will help in the tailored treatment of these patients and prevent complications of vitamin C deficiency on the one hand or hyperoxaluria secondary to vitamin C excess on the other.

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