Laboratory Test Reference Guide

Ascorbic acid (vitamin C) at very high concentrations can interfere. It is recommended that patients refrain from taking excessive amounts of vitamin C or vitamin C rich foods for at least 48 hours prior to urine collection.

Minimum of 10 ml required. If other tests requested, please send separate aliquot for Oxalate. Please send pottle, if no aliquoting required.

Acidified and Frozen. pH must be <2.

Patients < 16 years old       : 0 - 500 umol/L/24 hr /1.73 m2

Patients 16 years and older: 0 - 450 umol/L/24 hr/1.73 m2

The reference interval unit is umol/24h/1.73m2 but results are reported as umol/24h (number of characters is limited). The 2 units are fairly comparable in adults of average size but results should be adjusted for body size area (BSA) in children and adults at more extreme ends of weight (or size). Calculate the patients BSA using an online calculator( BSA calculator .) Adjusted result =  (reported 24h result x calculated BSA)/1.73

Oxalate

Hyperoxaluria from any cause can lead to renal stone formation and /or tubulointerstitial nephropathy.

CAUSES OF HYPEROXALURIA

Enteric hyperoxaluria: Over absorption of dietary oxalate is a consequence of fat malabsorption, due to chronic disease of the pancreas, biliary tract or small intestine, jejuno-ileal bypass, ileal resection, or bacterial overgrowth syndromes. With fat malabsorption, calcium in the bowel lumen is bound by fatty acids instead of oxalate, which is left free for absorption in the colon.  Treatment may include a low fat diet, pancreatic enzymes if deficient, and calcium supplements with meals.

Dietary excess of oxalate is a common cause of mild elevation of urine oxalate. The following foods have a high oxalate content and should be avoided by patients with hyperoxaluria or renal stones:

High oxalate foods

• beetroot
• bran (bran flakes, bran flour, bran meals, cereal bran, rice bran flour)
• chocolate, cocoa and drinking chocolate
• muesli
• nuts (all nuts, but especially peanuts, pecans and cashews)
• Ovaltine
• parsley
• rhubarb
• runner beans (large amounts)
• spinach
• strong tea (large amounts)

Hereditary (primary) hyperoxaluria is a rare cause of severe hyperoxaluria (>1 mmol/24h ; oxalate/creatinine ratio 250 - 2000). Patients usually present with recurrent calcium oxalate stones and renal failure during childhood.

Ethylene glycol is metabolised to oxalate; very high levels may be found in association with ethylene glycol poisoning

10 mL acidified urine.