LAUSR

BACKGROUND In patients with phaeochromocytomas or paragangliomas (PPGLs), 24-hour urine collections for metanephrines (uMNs) are cumbersome. OBJECTIVE To evaluate the diagnostic utility of ratios to creatinine of 'spot' uMNs. METHODS Concentrations of uMNs and plasma metanephrines (pMNs) were measured by HPLC-mass-spectrometry. We retrospectively compared correlations of 24-hour-urine output and ratio to creatinine in historical specimens, and prospectively assessed 24-hour and contemporaneous spot urines and, where possible, pMNs. Using trimmed log-transformed values, we derived reference intervals based on age and sex for spot urines. We used multiples of upper limit of normal (MULNs) to compare areas under curves (AUCs) for receiver-operator characteristic curves of individual, and sum and product of, components. RESULTS In 3143 24-hour-urine specimens on 2416 patients, the correlation coefficients between the ratios and outputs of metanephrine, normetanephrine and 3-methoxytyramine in 24-hour urines were 0.983, 0.905, 0.875, respectively. In 96 patients, the correlations between plasma concentrations, urine output and ratios in spot specimens were similar to those for raw output or ratios in 24-hour specimens. Among 160 patients with PPGLs, the confidence intervals for AUCs for individual metabolites overlapped for all four types of measurement, as did those for the sum of the MULNs although these were slightly higher (AUC for spot urine 0.838 (0.529-1), plasma 0.929 (0.874-0.984), output 0.858 (0.764-0.952)). CONCLUSIONS Ratios of fractionated metanephrines to creatinine in spot urine samples appear to have a similar diagnostic power to other measurements. The ease of spot urine collection may facilitate diagnosis and follow-up of PPGLs through improved patient compliance.