The BTA Trak Test is a quantitative immunoassay that measures bladder tumor antigen, human Complement Factor H related protein (hCFHrp), in the urine of bladder cancer patients. It is indicated for use as an aid in the management of bladder cancer patients in conjunction with cystoscopy. Currently it is marketed in a microtiter plate format, but Abbott Laboratories, Inc. is in the process of adapting the assay to the Abbott AxSYM immunoassay auto analyzer system.
Designed with the clinical laboratory in mind, the BTA Trak Assay requires no specimen stabilizers or sample preparation. The urine samples may be assayed fresh, held up to seven days refrigerated or frozen for longer storage, and batched to accommodate a wide variety of specimen transit times, laboratory work flow and volume throughputs. Sample collection, a random urine specimen collected in an ordinary urine sample collection cup, is convenient for the patient. The product has an extended shelf-life of 18 months from manufacture date.
The BTA Trak test kit, which includes all the reagents to perform the assay, uses common laboratory equipment. The microplate immunoassay employs the well established EIA technology. The kit calibrators, which are ready-to-use with known concentrations of bladder tumor antigen, are assayed along with the kit controls and patient urine samples. Samples may be assayed singularly or in duplicate following standard laboratory practice.
A point-to-point calibration curve is constructed and the concentration of bladder tumor antigen is quantified from the curve. Data analysis may be streamlined by using a variety of data reduction software capable of constructing a point-to-point curve.
The distribution of bladder tumor antigen was studied in urine samples using the BTA Trak Assay. Samples were collected from diverse geographic locations and stored frozen until tested. The overall sensitivity of the BTA Trak Assay was found to be 72 percent (n=216) in patients with transitional cell carcinoma (TCC) of the bladder as confirmed by histology. There is a strong correlation of bladder tumor antigen to the stage and grade of the tumor. A subset of confirmed bladder cancer patients studied (n=144) had voided urine cytology performed on the same urine sample evaluated in the BTA Trak Assay.
|Thickening of bladder epithelium by tumor cell proliferation (left). Nodule of tumor cells in the bladder (right).
The BTA Trak Assay results were shown to be more sensitive than voided urine cytology in all categories of stage Ta, T1, T2 and TIS and grade I, II, and III tumors. The specificity of the assay in healthy subjects was found to be 97 percent (n=212).
The reproducibility of the BTA Trak Assay was assessed according to National Committee for Clinical Laboratory Standards guideline EP5-T2, 1992. The results were determined by testing two controls and five samples in duplicate in each of 20 independent runs using two lots of reagent. The average within-run, between-run, and between-lot coefficient of variation was 5.2, 5.3 and 1.1 percent, respectively.
Dilution linearity was performed on 12 urine samples from TCC-positive patients. The samples were serially diluted with the zero calibrator and assayed using the BTA Trak Assay. Linear curve fit and regression analysis yielded correlation coefficients within the range of 0.989-1.000. Antigen recovery studies were performed with four TCC positive urines diluted into normal urine. The recovery ranged from 91.4 to 100 percent. The lower limit of detection was estimated to be 0.65 Units/ml of bladder tumor antigen and a clinical cut off was established at 14.0 Units/ml by receiver operator curve (ROC plot) analysis. No high-dose hook effect was observed in clinical urine samples with concentrations of bladder tumor antigen as high as 12,400 Units/ml.
The test is contraindicated for patients with renal disease (such as stones and nephritis), urinary tract infections, cystitis or renal cancer (including upper tract TCC), because positive results may occur. Hematuria and bladder tumor antigen levels in urine seems to be independent as reported by Enfield et al (Journal of Urology 159, No. 5, Suppl. 1998). The leakage of blood into the urine and the presence of hCFHrp appear to be independent events.
The biological role of hCFHrp is likely to be the same as that of Factor H (FH), the negative regulation of the alternative complement pathway, which protects the bladder from infections. Bladder, cervical and other tumor cells in culture produce and secrete hCFHrp (Clin. Res. 4:2511, 1998) that has the biological activity of FH. The resistance of the cancer cell lines to complement lysis is correlated to their production of hCFHrp, and can be overcome by antibodies to FH (J. Biol. Chem., May, 2000; In Press). Finally, bladder tumors have been shown to make CFHrp message by in situ hybridization and semi-quantitative RT-PCR (Cancer Res. 39:263, 1998). These data suggest that cancer cells produce CFHrp, and possibly other complement regulatory proteins, to prevent lysis by the immune system. The quantitative BTA Trak Assay and the companion qualitative BTA Stat Test measure the secreted hCFHrp produced by the tumor cells. Both tests were cleared for marketing by the Food and Drug Administration. The BTA Stat Test was the first tumor marker cleared for prescription home use.
Studies continue on the clinical quantitative significance of the antigen measurement. A retrospective serial monitoring study on 187 patients with a history of bladder cancer was published by Blumenstein et al (Journal of Urology Vol. 161, 57-61, 1999). It concluded that there was a statistically significant relationship between the serially assessed BTA Trak test levels and the hazard for diagnosis for bladder cancer recurrence (potential for recurrence). Recently a multi-center prospective serial monitoring study was completed, and publication of the results is expected in 2000.
Abbott Laboratories has signed an agreement to adapt the BTA Trak Assay to its automated immunoassay AxSYM system. The automated assay is expected to launch first in Europe and then in the United States. The BTA Trak assay is manufactured by Bion Diagnostic Sciences in its ISO 9001-registered facility in Redmond, Wash. and distributed by Polymedco Inc. of Cortlandt Manor, N.Y.
For additional information, Select No. 260 on the reader reply card, or contact Polymedco customer service at 800-431-2123 or 914-739-5400, visit its Web site at www.btastat.com or send e-mail to [email protected].