Validation Test for Plasma Oxalate Level in a Biochemical Laboratory at the Galilee Medical Center

Given the need to perform an oxalate plasma test in Israel, and being a leading center in the field of hyperoxaluria in Israel, the investigators are interested in placing the test in the biochemical laboratory at our institution but require validation levels in comparison with leading laboratory in Europe.

The source of oxalate in the body is endogenous production in the liver and nutrition. The oxalate is excreted in the urine by the kidneys. In situations where there is excess oxalate in the urine, it may crystallize together with calcium and settle as calcium-oxalate crystals in the kidney and cause kidney damage. If there is advanced kidney damage, the secretion of oxalate in the urine is impaired, and the oxalate accumulates in the blood and deposit in all the tissues of the body, including eyes, bones, bone marrow, blood vessels and more. Conditions in which there is a high level of oxalate in the body are caused by poisoning (ethylene glycol) or conditions of secondary hyperoxaluria such as in cystic fibrosis or inflammatory bowel diseases (there is increased absorption of oxalate in the intestine in cases of fatty diarrhea) or in primary hyperoxaluria.

Primary Hyperoxaluria is a group of diseases caused by increased excretion of oxalate by the liver, due to a genetic defect in the oxalate metabolism pathway in the liver. Hyperoxaluria type 1 (PH1) is the most severe of the whole group, and causes kidney failure in most patients by the second decade of life. The treatment of PH1 was until recently based on a liver transplant in order to restore a normal enzyme and in most cases a kidney transplant was also required. In November 2021, the FDA approved a breakthrough drug for hyperoxaluria, LUMASIRAN.

The Pediatric Nephrology Unit at the Galilee Medical Center is a specialist center for hyperoxaluria. The incidence of the disease in the population in the Galilee is one of the highest in the world and as a result a lot of experience has been accumulated in treating the disease in our center.

Also, the pediatric nephrology unit was used as a center in the ALNYLAM company's clinical research to test the efficacy and safety of the drug LUMASIRAN. There are now eight PH1 patients receiving the new drug (through research or through the health basket) who are being monitored in the pediatric nephrology unit at our institution.

Testing the oxalate level in the plasma is required mainly in cases of hyperoxaluria patients, mainly for the purpose of monitoring the response to treatment or in preparation for a decision on a kidney transplant. There are other situations in which it is important to perform the test as mentioned above, but these are rarer situations. In Israel there is no laboratory that tests the level of oxalate in plasma.

There are several laboratories, among them the biochemistry laboratory at the Galilee Medical Center, that perform an oxalate level test in the urine. The urine test is performed as an initial survey in situations where hyperoxaluria is suspected and as part of the investigation of kidney stone disease.

In the period before the appearance of the drug treatment for PH1, when the definitive treatment was based on a liver transplant, it was customary to monitor only oxalate in the urine in Israel. In the USA and Europe, it was customary to monitor plasma oxalate levels after a liver transplant, and when the level dropped to a value close to normal, it was recommended to proceed with a kidney transplant. In situations where a liver and kidney were donated from the deceased, it was not acceptable to delay the kidney transplant, and there were centers that used to perform dialysis for a certain period after Liver-kidney transplantation while monitoring plasma oxalate levels In Israel, as mentioned, it was not customary to perform dialysis after liver/liver-kidney transplantation and it was not customary to monitor plasma oxalate levels after transplantation.

The situation changed after the approval of the new drug treatment. Lumisiren entered the health basket in Israel in 2022 for all PH1 patients. The treatment replaces the liver transplant and as a result there is a need to monitor oxalate levels in the plasma in the following situations:

1. To monitor the response to lumsiren treatment in a dialysis patient who does not urinate (therefore it is not possible to monitor the decrease in oxalate in the urine)
2. In preparation for a kidney transplant in a PH1 patient with advanced kidney failure who is being treated with lumsiran. According to the latest recommendations, it is necessary to wait for the decrease of oxalate in the plasma to a value lower than 70 micromol/liter before a kidney transplant
3. After a kidney transplant in a patient treated with lumesiren, for the purpose of risk assessment and the need for dialysis after the transplant in order to protect the kidney if there are high levels of oxalate in the plasma.

Testing oxalate in plasma is not simple compared to testing the level in urine because the values in urine are an order of magnitude higher than in plasma (in urine values of mmol/liter and in plasma micromol/liter) and the tests available on the market are more sensitive at the higher concentrations. In addition, oxalate is unstable: there is a transition of ascorbic acid to oxalate in a relatively basic environment (4pH\>) and therefore acidification of the plasma is required during the test preparation phase.

The kit used to test oxalate in urine in our biochemical laboratory is based on the enzyme oxalate oxidase and color reaction (coulometric) and was purchased from Biotech Trinity. According to the manufacturer's instructions, the kit is intended for testing the oxalate level in urine. This test is performed in our laboratory and has undergone internal validation according to the manufacturer's instructions.

There are two types of tests for oxalate level in plasma in laboratories in the world - There are laboratories that use the enzymatic test based on the TRINITY BIOTECH kit and spectrophotometry, and there are laboratories that use the mass spectrometry method (gas or ions).

The second method (mass spectrometry) is considered accurate for oxalate in plasma but is quite expensive and not available to our laboratory. The use of oxalate oxidase enzyme is accepted in research and for clinical needs in leading laboratories in the world.

In the biochemical laboratory at CHARITE University hospital in Berlin, there is extensive use of oxalate tests in plasma for clinical and research purposes. The Nephrology Laboratory and Department at CHARITE Hospital are considered world leaders in the field of hyperoxaluria, and published studies where plasma oxalate was measured with the enzymatic method in the TRINITY kit.

Given the need to perform an oxalate plasma test in Israel, and being a leading center in the field of hyperoxaluria in Israel, the investigators are interested in placing the test in the biochemical laboratory at our institution. In accordance with the means available to the laboratory here and after testing the efficiency and reliability of the enzymatic test based on oxalate oxidase, the investigators decided to validate the oxalate plasma test in our laboratory. Since the manufacturer designates the kit for urine testing only, it is not possible to perform validation based on the manufacturer's test kits and the investigators needed external validation. In the pilot tests run so far, the investigators have received acceptable values according to the patient's clinical condition.

Prof. Knopf from CHARITE Hospital in Berlin generously agreed to perform an external validation for us for the plasma oxalate test performed in our biochemical laboratory.

Methods:

Number of samples: a total of 30 blood samples will be taken, from 30 different patients. The samples will be taken from a variety of patients in order to obtain a wide range of plasma oxalate levels. About 10 samples will be taken from healthy volunteers, about 10 samples from dialysis patients without a background of hyperoxaluria, about 5 samples from hyperoxaluria patients receiving drug treatment or after a liver transplant, and about 5 samples from advanced kidney failure patients not on dialysis.

The test protocol - attached in the appendix. The protocol is compatible with the laboratory where the external validation will be performed.

Each sample will be sterilized immediately and the plasma will be divided into two test tubes and kept frozen (-80). One test tube will be sent for testing in the laboratory in Berlin and one test tube will stay here and be tested in our laboratory.

The step of treating the sample until freezing is the same as it will be performed here.

The sample handling process in the laboratory here will be performed by one laboratory employee.

The samples will be sent frozen to the laboratory in Berlin. The second step - treatment of the sample after thawing - will be carried out according to an agreed protocol between the two laboratories, in order to avoid differences in the treatment of the sample. Also, the investigators will coordinate the days of the tests between the two laboratories in order to avoid a difference arising from the preservation time of the samples in the freezer.

The protocol was written jointly by us with the laboratory in Berlin. The shipment of the samples will be financed by the Medison Pharmaceuticals as part of its support for the project to raise awareness and improve service for hyperoxaluria patients in the Galilee.

Statistics - after receiving the test answers from Berlin, the investigators will compare the results obtained there and here using the following tests:

Quantitative data will be described using means and standard deviations, median, interquartile range (IQR), and range.

Comparison tests for paired samples - to examine the differences between two paired samples using the paired sample T test (if the differences are normally distributed) or the Wilcoxon signed rank test if the distribution of the differences is not normal. A 95% confidence interval will be calculated for the difference between the paired samples.

Correlation tests - to test the relationship between the paired samples. Pearson's correlation coefficient test or alternatively Spearman's correlation coefficient test (will be chosen according to the size of the sample and the shape of the distribution) Bland-Altman plot and Scatter plot curves were used to demonstrate the difference between the results.

A P value lower than 5% will be considered statistically significant.

Maintaining anonymity: the samples will be marked with a code given here, without identifying details on the forms or the test tubes. The coding table will be kept separately on the principal researcher's computer and in a separate binder in the research coordinator's closet.

Informed consent: The volunteers will sign an informed consent form after an explanation of the meaning of the test.

Eligibility Criteria:
Inclusion Criteria:

* Signing the informed consent

Exclusion Criteria:

* Not willing to participate