Printer Friendly

[beta]-trace protein in serum: a new marker of glomerular filtration rate in the creatinine-blind range.

Recent studies have shown that low-molecular weight proteins in serum seem to be better markers for detecting reduced glomerular filtration rate (GFR) than the conventional measurement of serum creatinine (1, 2). Several proteins, such as ribonuclease, [alpha].sub.1]-microglobulin, [[beta].sub.2]-microglobulin (B2M), and cystatin C have been compared with serum creatinine (2, 3). Whereas serum creatinine is increased only after a reduction of ~50% in GFR, the above proteins, especially cystatin C, are already increased within that so-called creatinine-blind range (1, 4-6). Recently, another low-molecular weight protein, the [beta]-trace protein (BTP), isolated primarily from cerebrospinal fluid (7), was shown to be increased in patients with renal diseases (8, 9). However, there is no information on the relationship of BTP and a standard measure of GFR such as inulin clearance. Therefore, to investigate the potential clinical usefulness of BTP for early detection of reduced GFR, we have performed corresponding measurements of BTP and inulin clearance.

The study included 115 diabetic patients (44 women; mean age, 53.4 years; 71 men, mean age, 52.9 years); 57 had type I diabetes and 58 had type II. GFR was determined by measuring the inulin clearance. A priming dose of 2.5 g of inulin (Inutest; Laevosan) was administered intravenously within 30 s, followed by a constant infusion (15 mL/h) of inulin at a rate dependent on serum creatinine (infusion rate, 1.5 g/h for serum creatinine concentrations <130 [micro]mol/L; 0.75 g/h for serum creatinine concentrations between 130 and 265 [micro]mol/L; and 0.38 g/h for serum creatinine concentrations between 265 and 450 [micro]mol/L).

After 30 min for equilibration and after the patients were instructed to empty their bladders, two spontaneously voided urine samples were collected at 60-min intervals. Blood samples were taken before bolus injection as well as at the beginning and at the end of each urine collection period. After centrifugation (1600g for 15 min), samples of serum and urine were stored at -80[degrees]C until analysis. A fully enzymatic assay for the quantification of inulin was used (10). GFR was calculated by taking the mean of the two clearances and correcting that value to 1.73 [m.sup.2] of body surface area. Serum creatinine concentrations were determined by an enzymatic method, and B2M was determined by a turbidimetric method; both methods were performed on a Hitachi 717 analyzer with reagents supplied by Boehringer Mannheim (Creatinine plus and Tina-quant [[beta].sub.2]-microglobulin). Controls with assigned values showed interassay imprecision (CV) of <5%.

For determination of BTP, a newly developed nephelometric research assay was performed on a BNA II analyzer (Dade Behring Marburg). This assay is based on the principle of latex particle-enhanced immunonephelometry using rabbit polyclonal antibodies against BTP. Calibration of the assay is based on highly purified BTP from cerebrospinal fluid characterized by amino acid sequencing and quantitative amino acid analysis. For the default sample dilution of 1:100, the basic measuring range is ~0.25-15.8 mg/L. The total analytical imprecision (intraassay plus interassay; n = 40) of the assay, calculated from two control materials and three serum samples with concentrations of 1.51-7.89 mg/L, was between 2.33% and 6.5%.

Statistical calculations were performed with SPSS 7.5 for Windows (SPSS Software). The diagnostic validity was evaluated by the ROC curve analysis. GraphROC for Windows, Ver. 2.1, was used for calculations of areas under the curves (11). Regression analysis was performed with the EVAPAK for Windows software, Ver. 3.01 (12). P <0.05 was considered statistically significant. The study was performed in accordance with ethics standards of the Helsinki Declaration of 1975 (revised in 1985).

The GFR was <80 mL/min in 41 patients and >80 mL/min in 74 patients, which was considered as the lower cutoff limit of GFR. BTP showed curvilinear behavior in relation to GFR, as did creatinine and B2M (Fig. 1, A-C). There were significant correlations between GFR and the reciprocal concentrations of creatinine, B2M, and BTP (r = 0.666, 0.514, and 0.672, respectively; P <0.05); the differences between the correlation coefficients, however, were not statistically significant (P >0.05). The median values (and ranges) were 88 [micro]mol/L (49-331 [micro]mol/L) vs 69 [micro]mol/L (33-137 [micro]mol/L) for creatinine, 2.17 mg/L (0.51-12.1 mg/L) vs 1.44 mg/L (0.85-3.59 mg/L) for B2M, and 0.82 mg/L (0.44-6.44 mg/L) vs 0.52 mg/L (0.32-1.09 mg/L) for BTP and differed significantly between the two groups (Mann-Whitney U-test, P <0.0001). For BTP, an upper 97.5% reference limit of 0.79 mg/L was calculated by both parametric and nonparametric approaches (13) considering patients with GFR values >80 mL/min as individuals with normal GFR. Fig. 1D shows ROC curves of the three analytes to discriminate between patients with normal (>80 mL/min) and reduced (<80 mL/min) GFR values. The curve of BTP is above the curves of creatinine and B2M. The area under the BTP curve is significantly higher than the areas under the two other curves, demonstrating a higher power of discrimination (P = 0.042). When the point with the highest diagnostic efficiency (0.79 for creatinine and B2M, 0.81 for BTP) was selected as the optimal decision limit, the threshold was 91 [micro]mol/L for creatinine, 2.34 mg/L for B2M, and 0.64 mg/L for BTP. The corresponding diagnostic sensitivities and specificities were 49% and 96% for both creatinine and B2M and 76% and 84% for BTP.


In summary, our data support the view that BTP may be suitable as an indicator of reduced GFR even in the creatinine-blind range. Additional detailed studies are required, but are worthwhile because the search for improved markers of GFR continues (14).

This work was supported in part by the Fund of the German Chemical Industry (Grant 400770 to K.J.) and includes parts of the doctoral thesis of F.P.


(1.) Norlund L, Fex G, Lanke J, von Schenck H, Nilsson JE, Leksell H, Grubb A. Reference intervals for the glomerular filtration rate and cell-proliferation markers: serum cystatin C and serum [[beta].sub.2]-microglobulin/cystatin C-ratio. Scand J Clin Lab Investig 1997;57:463-70.

(2.) Jung M, Jung K. Niedermolekulare Proteine im Serum als Marker der glomerularen Filtrationsrate: Cystatin C, [alpha]-1-Mikroglobulin and [beta]-2-Mikroglobulin. Lab Med 1994;18:461-5.

(3.) Newman DJ, Thakkar H, Edwards RG, Wilkie M, White T, Grubb A, Price CP. Serum cystatin C measured by automated immunoassay: a more sensitive marker of changes in GFR than serum creatinine. Kidney Int 1995;47: 312-8.

(4.) Finney H, Newman DJ, Gruber W, Merle P, Price CP. Initial evaluation of cystatin C measurement by particle-enhanced immunonephelometry on the Behring nephelometer systems (BNA, BN II). Clin Chem 1997;43:1016-22.

(5.) Kyhse-Andersen J, Schmidt C, Nordin G, Andersson B, Nilsson EP, Lindstrom V, Grubb A. Serum cystatin C, determined by a rapid, automated particle-enhanced turbidimetric method, is a better marker than serum creatinine for glomerularfltration rate. Clin Chem 1994;40:1921-6.

(6.) Pergande M, Jung K. Sandwich enzyme immunoassay of cystatin C in serum with commercially available antibodies. Clin Chem 1993;39:1885-90.

(7.) Clausen J. Proteins in normal cerebrospinal fluid not found in serum. Proc Soc Exp Biol Med 1961;107:170-2.

(8.) Hoffmann A, Nimtz M, Conradt HS. Molecular characterization of 0-trace protein in human serum and urine: a potential diagnostic marker for renal diseases. Glycobiology 1997;7:499-506.

(9.) Melegos DN, Grass L, Pierratos A, Diamandis EP. Serum prostaglandin D synthase concentration is elevated in humans with renal impairment [Abstract]. Clin Chem 1998;44:A20.

(10.) Kuehnle HF, von Dahl K, Schmidt FH. Fully enzymatic inulin determination in small volume samples without deproteinization. Nephron 1992;62:104-7.

(11.) Kairisto V, Poola A. Software for illustrative presentation of basic clinical characteristics of laboratory tests--GraphROC for Windows. Scand J Clin Lab Investig 1995;55(Suppl 222):43-60.

(12.) Passing H, Bablok W. A new biometrical procedure for testing the equality of measurements from two different analytical methods. Application of linear regression procedures for method comparison studies in clinical chemistry. Part I. J Clin Chem Clin Biochem 1983;21:709-20.

(13.) Solberg HE. Approved recommendations (1987) on the theory of reference values. Part 5. Statistical treatment of collected reference values. Determinations of reference limits. J Clin Chem Clin Biochem 1987;25:645-56.

(14.) Swan SK. The search continues--an ideal marker of GFR [Editorial]. Clin Chem 1997;43:913-4.

Friedrich Priem, [1] Harald Althaus, [4] Maria Birnbaum, [2] Pranav Sinha, [1] Harald S. Conradt, [5] and Klaus Jung (3) *

Departments of [1] Laboratory Medicine, [2] Nephrology, and [3] Urology, University Hospital Charit [6], Humboldt University Berlin, 10098 Berlin, Germany; [4] Dade Behring Marburg GmbH, 35001 Marburg, Germany; and [5] Gesellschaft fur Biotechnologische Forschung, Department of Protein Glycosylation, 38124 Braunschweig, Germany; * address correspondence to this author at: Department of Urology, Research Division, University Hospital Charite, Humboldt University Berlin, Schumannstrasse 20/21, 10098 Berlin, Germany; fax 4930-2802-1402, e-mail
COPYRIGHT 1999 American Association for Clinical Chemistry, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1999 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Technical Briefs
Author:Priem, Friedrich; Althaus, Harald; Birnbaum, Maria; Sinha, Pranav; Conradt, Harald S.; Jung, Klaus
Publication:Clinical Chemistry
Date:Apr 1, 1999
Previous Article:Within- and between-subject variation in commonly measured anthropometric and biochemical variables.
Next Article:Chronic lymphocytic leukemia cells may interfere in a glycated hemoglobin assay based on fluorescence quenching.

Related Articles
Membranous nephropathy associated with psoriasis.
A novel equation to estimate glomerular filtration rate using beta-trace protein.
Recent developments in the evaluation of glomerular filtration rate: is there a place for [beta]-trace?
Trimolecular complexes of [lambda] light chain dimers in serum of a patient with multiple myeloma.
Fetal urine cystatin C as a predictor of postnatal renal function in bilateral uropathies.
Reference interval for serum cystatin C in children.
Paradoxical changes in cystatin C and serum creatinine in patients with hypo- and hyperthyroidism.
[beta]-trace protein, cystatin C, [[beta].sub.2]-microglobulin, and creatinine compared for detecting impaired glomerular filtration rates in...
Low-molecular weight proteins as markers for glomerular filtration rate.
[beta]-trace protein is not better than cystatin C as an indicator of reduced glomerular filtration rate.

Terms of use | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters