Urine TGF- beta1 assay validation: spinning down urine samples could diminish TGF-beta1 signal.

TGF-beta1 is a mediator of immune and anti-inflammatory responses. The present research was dedicated to the validation of the urine Quantikine Human TGF-beta1 ELISA assay.A reference interval was developed utilizing 100 urine samples from healthy donors. Samples containing precipitate were centrifuged and supernatants or un-spun specimens were run with TGF-beta1 assay.Supernatant TGF-beta1 concentrations are only a fraction of the un-spun sample values (77% to 29%, even less for the low concentration samples). Validation involving un-centrifuged urine samples demonstrated the following TGF-beta1 assay characteristics: linearity from 23 to 1286 pg/mL, recovery from 95 to 116%; precision: < 17%; analytical specificity 3 pg/mL; reference interval from 0 to 39 pg/mg creatinine; freeze-thaw stability: after first thawing, urine samples could loose from 5 to 40% of TGF-beta1 activity on each following freeze-thaw circle.For TGF-beta1 assay, urine sample preparation should not include a centrifugation step; repeating freeze-thawing should be avoided.