Q J Med 2003; 96: 363-367
© 2003 Association of Physicians
Urinary retinol binding protein in Indo-Asian patients with idiopathic interstitial nephritis
From the Renal Unit, St Mary's Hospital, London, 1 Department of Chemical Pathology, St Helier Hospital, Carshalton, and 2 Department of Clinical Biochemistry, Addenbrookes Hospital, Cambridge, UK
Received 24 June 2002 and in revised form 29 January 2003
Background: Idiopathic interstitial nephritis (IIN) is common in the UK Indo-Asian population. Lack of systemic involvement and unremarkable urinalysis on stick testing suggest that it may underlie some cases of end-stage renal failure of undetermined cause. If IIN is diagnosed early, prompt initiation of treatment can improve long-term outcome.
Aims: To investigate whether urinary retinol binding protein (RBP) is elevated more commonly than urinary albumin in IIN, and might be useful in the early detection of renal disease in Indo-Asian patients.
Design: Preliminary observational study
Methods: We measured urinary RBP and urinary albumin in 19 Indo-Asian patients in whom a renal biopsy had shown IIN, 10 of whom had already been treated with corticosteroids at the time of specimen collection. A further 28 Indo-Asian patients with glomerular disease, and six with normal light-microscopic renal biopsy, were assessed in parallel.
Results: Urinary RBP/creatinine ratio (RCR) was elevated in all 19 cases of IIN, compared to 12/19 in whom the albumin/creatinine ratio (ACR) was elevated. Elevated urinary RBP was thus significantly more common than albuminuria in this group (p<0.01). Twelve of the 19 cases also satisfied the criteria for tubular proteinuria. RCR was elevated to >30 times the upper limit of normal in 7/9 who had not previously received corticosteroids, of whom four had normal ACR; none had ACR >5 times the upper limit of normal.
Discussion: These data suggest that measurement of urinary RBP should be explored as an adjunct to albuminuria, if screening for renal disease in the Indo-Asian population is contemplated.
Address correspondence to Dr S.T. Ball, Renal Unit, University Hospitals Birmingham, Edgbaston, Birmingham B15 2TH. e-mail: Simon.Ball{at}uhb.nhs.uk