title: Urine oxalate biological variation in patients with primary hyperoxaluria.
abstract: Hyperoxaluria is a well-recognised risk factor for urolithiasis and patients with primary hyperoxaluria (PH) gradually build up calcium oxalate deposits leading to chronic kidney disease. Efforts to improve treatment for PH have focused on reducing urine oxalate excretion and thus decreasing lithogenesis. To determine the efficacy of treatments designed to alter a biochemical parameter it is necessary to know the biological and analytical variation of that parameter. In this study, we estimated the intra-individual biological variation of urine oxalate excretion in patients with PH, and from this determined what would constitute a significant change in the form of a reference change value (RCV). Each patient collected four 24-h urines on consecutive weeks. The intra-individual biological variation of oxalate excretion calculated from these samples ranged from 0 to 36 % with a mean of 14 %. The corresponding RCVs were 4-84 % with a mean of 32 %. This result implies that, on average, a reduction of almost one-third in urine oxalate excretion is required to prove an effect from treatment. The wide range of biological variation between individuals may reflect other, as yet unknown, determinants of oxaluria in PH, as well as inaccuracies in urine collection. The data suggest that it is more appropriate to use individual RCVs established prior to treatment to determine its efficacy: a relatively small fall in urine oxalate excretion may be outside the biological variation of some patients but not of others.
authors: Clinical Biochemistry, University College London Hospitals, 60 Whitfield Street, London, W1T 4EU, UK. Oliver.clifford-mobley@nhs.net.
authors: Oliver
authors: O
authors: Clifford-Mobley
authors: OxThera AB, Sturegatan 56, 114 36, Stockholm, Sweden.
authors: Anna
authors: A
authors: Sjögren
authors: OxThera AB, Sturegatan 56, 114 36, Stockholm, Sweden.
authors: Elisabeth
authors: E
authors: Lindner
authors: Clinical Biochemistry, University College London Hospitals, 60 Whitfield Street, London, W1T 4EU, UK.
authors: Gill
authors: G
authors: Rumsby
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D006801:Humans; D006960:Hyperoxaluria, Primary / Q000652:urine*; D010070:Oxalates / Q000652:urine*; D055815:Young Adult
chemical_list: D010070:Oxalates
keywords: Biological variation; Primary hyperoxaluria; Reference change value; Urine oxalate