Pseudo-hypoalbuminemia in peritoneal dialysis patients

Introduction: Oxidative stress in peritoneal dialysis (PD) patients produces molecular modifications of serum albumin that disturb its biological functions and interfere with its detection by the commonly used bromocresol green (BCG) assay. This study aimed to evaluate the role of oxidized serum albumin (OSA) in hypoalbuminemic PD patients. Methods: Twenty four PD stable patients with serum albumin levels measured by BCG assay (SA_CBCG) ≤ 3.0 g/dl enrolled in the study. Serum albumin, OSA, oncotic pressure, hydration status, lean tissue index (LTI), normalized protein equivalent of total nitrogen appearance (nPNA) and high sensitivity C-reactive protein (hsCRP) were determined. OSA was assessed by a specific albumin detection index (ADI). ADI was defined as the ratio between the readout of the non-oxidized serum albumin measured by the BCG assay (SA_CBCG) to the total (non-oxidized and oxidized) serum albumin concentration in the fraction that determined by absorbance at 280 nm (OD280) (TSAC_OD280): ADI = SA_CBCG/TSAC_OD280. When the SA_CBCG decreased, as a result of the oxidation of serum albumin, the ADI will be < 1. When low serum albumin levels was determined by the BCG assay (SA_CBCG) in hypoalbuminemic PD patients with ADI < 1, it was usually refers to “pseudo” hypoalbuminemia because it is not includes the OSA fraction. To establish a diagnosis of true hypoalbuminemia, the total serum albumin including the non-oxidized and oxidized fractions (TSAC_OD280) should be determined. Participants were assigned to two groups according to their ADI (< 0.5 or ≥ 0.5). Results: Both study groups were comparable in age, BMI, gender, presence of diabetes, PD modality, peritoneal membrane characteristics, Kt/v, residual renal function (RRF), PD vintage and serum albumin levels. All participants had ADI < 1.0 and, therefore, had “pseudo” hypoalbuminemia. Mean ADI was 0.53±0.12 in all patients, 0.43±0.01 in patients with ADI < 0.50 and 0.62±0.03 in patients with ADI ≥ 0.50 (P < 0.001). Extracellular/Intracellular water ratio (E/I ratio) was lower in patients with ADI < 0.5 than in patients with ADI ≥ 0.5 (P = 0.002). Oncotic pressure and hsCRP were higher in patients with ADI < 0.5 than in patients with ADI ≥ 0.5 (P = 0.024, P = 0.032, respectively). nPNA, RRF and LTI were similar in both groups. Conclusions: “Pseudo” hypoalbuminemia, results from the presence of undetectable OSA fraction by the BCG assay, seems to be a very common finding and may mislead medical staff decisions in PD patients. Although OSA may contribute to better oncotic pressure and hydration status of these patients, its pathogenic ability to accelerate atherosclerosis should be kept in mind.