Urinary β-Trace Protein as a New Renal Tubular Marker

Abstract

Recently, lipocalin-type prostaglandin D synthase, or β-trace protein (BTP),1 has been introduced as a marker to predict the glomerular filtration rate. BTP catalyzes the isomerization of prostaglandin H2 to prostaglandin D2 and is a lipocalin lipid-transporter protein that binds retinoids, thyroid hormones, and bile pigments. It has been detected in cerebrospinal fluid, serum, urine, amniotic fluid, and seminal plasma (1). Like other proteins of low molecular mass, BTP is almost completely filtered through the glomerulus and then completely reabsorbed through the tubules. Because of its molecular mass (23–29 kDa), its constant production rate, and its stability, BTP shares many properties of an ideal marker protein of tubular function. We therefore explored the diagnostic use of BTP as a novel urinary marker in comparison with that of α1-microglobulin (A1M), a conventional indicator of tubular function (2)(3)(4). We used a Behring Nephelometer II analyzer (Dade Behring) with a latex particle–enhanced fixed-time immunonephelometric method to assay BTP in urine (measurement range, 0.21–13.6 mg/L) and obtained an interassay imprecision of 4.5% at 1.88 mg/L. A Behring Nephelometer II analyzer was also used to measure urinary albumin by immunonephelometry. Urinary A1M, creatinine, and total protein …