Circulating Oxalate Levels in Short Bowel Syndrome as a Severity Marker of CKD

Patients with short bowel syndrome (SBS) may exhibit enteric hyperoxaluria (EH), and the prevalence of oxalate nephropathy in SBS is likely underestimated. Plasma oxalate (POx) is a surrogate of systemic oxalate deposition and, consequently, may increase the risk of developing chronic kidney disease (CKD). The main objective of this study was to explore the distribution of POx levels in patients with SBS.

Patients followed for SBS were recruited prospectively in the OXAGO study (NCT04119765) to assess POx during their annual renal follow-up including iohexol clearance. The inclusion criteria were age ≥18 years, and SBS type 2 and type 3 for more than 6 months.

A total of 47 patients were included but only 45 patients has a measured POx (55% males, 80% SBS type 2, 66% parenteral nutrition, 61% kidney stone history). POx levels were 6.8 ± 4.4 μmol/l, 29% of patients had POx ≥5 μmol/l. In the whole cohort, mean urinary oxalate (UOx) was 648±415 and 54% were >500 μmol/24h. In the group of patients with high POx levels (HPO), 24-hour urine oxalate was significantly higher than in the group with normal POx levels (NPO) (919 ± 566 vs. 526 ± 257 μmol/l; P = 0.003). Glomerular filtration rate (GFR) was 66 ± 22 ml/min per 1.73 m², and 91% had CKD. GFR was significantly lower in the HPO than in the NPO group (49 ± 23 vs. 73 ± 18 ml/min per 1.73 m²; P = 0.0005.

Patients with SBS can display increased POx levels even with GFR >30 ml/min per 1.73 m². POx may be an interesting biomarker to assess the severity of EH.