Oxalic Acid, Adult, Urine with Creatinine (10456X)

Test Code

10456N

CPT Codes
83945, 82570

Includes

Creatinine

Preferred Specimen

10 mL urine with 6N HCl collected in a sterile, leak-proof container

Patient Preparation
Patient should refrain from taking excessive amounts of ascorbic acid or oxalate-rich foods (i.e. spinach, coffee, tea, chocolate, rhubarb) for at least 48 hours prior to the collection period

Minimum Volume

2 mL

Other Acceptable Specimens

Urine no preservative or preservative added after collection

Instructions

Please submit 10 mL of a well-mixed random collection. Adjust pH to <3.0 with 6N HCl prior to aliquoting for testing. Refrigerate after collection. For Pediatric patients order test code 11222-Oxalic Acid, Pediatric, Urine w/Creatinine. Add 2 mL 6N HCL per 100 mL Urine.

Transport Temperature

Room temperature

Specimen Stability

Room temperature: 7 days
Refrigerated: 7 days
Frozen: 24 days

Methodology
Spectrophotometry (SP)

Setup Schedule

Set up: Tues-Sat; Report available: 1-3 days

Clinical Significance

This quantitative oxalic acid test, performed with a random urine specimen, may help screen for hyperoxaluria, determine the cause of kidney stones, and assess kidney function in adults [1]. However, 24-hour urine specimens are generally preferred to random specimens when measuring oxalic acid for diagnostic evaluation and monitoring of hyperoxaluria [1,2].

Oxalic acid is an organic compound that naturally exists in many food sources. Because humans cannot metabolize oxalic acid, it must be excreted in urine as oxalate (the ionic form of oxalic acid). Excessive excretion of oxalates is called hyperoxaluria and can be attributed to primary or secondary causes. Primary hyperoxaluria (PH) is a rare condition resulting from enzymatic defects and can lead to chronic kidney disease, which may progress to kidney failure. Secondary hyperoxaluria can be caused by fat malabsorption, which may be due to inflammatory bowel disease, extensive resection of the small bowel, or excessive ingestion of substances that increase serum oxalates [3].

PH is associated with significant morbidity and mortality, including end-stage kidney disease [1].Early diagnosis is associated with better outcomes, but more than 40% of PH diagnoses are delayed [1]. Screening for PH may be considered for adults with recurrent calcium oxalate stones or family history of stone disease [1].

Urinary oxalic acid measurements may be inaccurate when estimated glomerular filtration rate declines [1]. Therefore, in patients with chronic kidney disease, plasma oxalate may be measured to help support the diagnosis of PH [1].

Results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

References
1. Bhasin B, et al. World J Nephrol. 2015;4(2):235-244.
2. Williams JC Jr, et al. Urolithiasis. 2021;49(1):1-16.
3. Shchelochkov O, et al. Defects in metabolism of amino acids. In: Kliegman R, et al. Nelson Textbook of Pediatrics. 21st ed. Elsevier; 2019:720-722.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.