Stability of urinary fractionated metanephrines and catecholamines during collection, shipment, and storage of samples

Background: Measurements of 24-h fractionated urinary metanephrines and catecholamines are used for the diagnosis of pheochromocytoma, but adequate information is needed regarding collection, storage, and shipment conditions. Methods: Spot urine samples were collected from 8 healthy volunteers. Aliquots were immediately frozen at -20 degrees C, or acidified to pH 4 and then frozen either directly or after 24 h at room temperature. The remaining urine was left at room temperature for 24 h and then split into one portion that was acidified and one portion that was not. Aliquots were either frozen or allowed to stand at room temperature for an additional 24, 48, 72, 96, and 168 h before freezing. We also tested the efficacy of adding Na(2)EDTA and Na2S2O5, as an alternative to acidification for preservation of the catecholamines. Results: No clinically relevant degradation (< 5%) was observed for the fractionated metanephrines under any of the storage conditions. In contrast, in similar to 50% of the untreated samples catecholamines were partially degraded during the first 24 h at room temperature. Immediate acidification, however, prevented degradation, whereas acidification after 24 h prevented further decay. Addition of Na(2)EDTA and Na2S2O5 fully prevented degradation of catecholamines during the first 24 h in 4 of 5 cases. In the remaining case, degradation did not exceed 10%. Conclusion: Preservation of samples for measurements of urinary fractionated metanephrines is not necessary if samples are assayed or frozen within 1 week, which is an important advantage if transport of samples is necessary. In contrast, urinary catecholamines require preservation measures during collection. (c) 2007 American Association for Clinical Chemistry