Urinary Retinol Binding Protein: Stability and Pre-Analytical Handling of Specimens for its Measurement

Abstract

SUMMARY. The stability of retinol binding protein (RBP) in urine has been reassessed and was found to be pH-dependent, diminishing as urinary pH decreased. When urines were incubated at 4°C for 1 week, statistically significant losses of RBP were observed at pH values less than seven, varying in degree in different urines. At 37°C some urine specimens showed minor losses when incubated for periods up to 4 h. This was more marked at pH 5 than pH 7 with maximum losses of 260/0 and 12%, respectively. When adjusted to pH 7, urines showed no significant loss of RBP when stored at 4°C for up to 2 weeks; at -20°C no significant change in RBP concentration was found for at least 14 weeks. To minimize losses of RBP it is recommended that urine pH is adjusted to above seven immediately after voiding. Additional key phrases: low molecular weight proteins; tubular proteinuria; pH stability; ELISARenal tubular function has been assessed by the measurement of proteins of low molecular weight (less than 40 kD) in urine. In health, these are readily filtered by the glomerulus and then reabsorbed by proximal tubular cells where they undergo catabolism.

Robust measurement of vitamin A status in plasma and blood dried on paper

“…We hypothesise that reasons could involve the dissociation of retinol from its binding protein in acidic conditions which increases retinol abundance during extraction. This is supported by the findings of Guy et al [17] who reported that urinary retinol binding protein is pH dependent, and is most unstable at pH 5-7.…”

Effect of nicorandil on proteinuria in well controlled hypertensive patients

“…To assess the roles of glomerular and tubular function in reduction of urinary protein excretion, we measured the changes of urinary immunoglobulin G (IgG) as a glomerular marker and retinol-binding protein as a tubular marker. Because 24-h urine samples would entail samples remaining at 378C for several hours, which leads to the potential for significant losses of retinolbinding protein in the bladder [22], a random sample during daytime was collected instead. Polyclonal antibodies raised in rabbits against retinol-binding protein were obtained from Assaypro Ulc Company (Winfield, Missouri, USA).…”

Urinary Excretion of Albumin and Retinol Binding Protein in Systemic Lupus Erythematosus

“…We are now able to measure specific proteins as markers of glomerular and Correspondence: Mr J M Guy. 668 tubular disease to facilitate the earlier detection of renal disease. For this reason, several workers have advocated the measurement of specific urinary proteins, notably albumin 16 which has been particularly exemplified in the assessment of diabetic nephropathy." 9 The few reports describing the use of specific urine protein measurement in SLE are conflicting.…”