Biological variation of methylmalonic acid in urine in spanish population.

Background-aim: Methylmalonic acid (MMA) is currently the best biomarker of functional vitamin B12 deficiency. However, for a correct interpretation of the patient's results it is necessary to know its biological variation (BV). No BV data are available for urine MMA values, as measured by mass spectrometry.

Stability of serum, plasma and urine osmolality in different storage conditions: Relevance of temperature and centrifugation.

Background: Osmolality reflects the concentration of all dissolved particles in a body fluid, and its measurement is routinely performed in clinical laboratories for the differential diagnosis of disorders related with the hydrolytic balance regulation, the renal function and in small-molecule poisonings. The aim of the study was to assess the stability of serum, plasma and urine osmolality through time and under different common storage conditions, including delayed centrifugation.

Methods: Blood and urine samples were collected, and classified into different groups according to several preanalytical variables: serum or plasma lithium-heparin tubes; spun or unspun; stored at room temperature (RT), at 4°C or frozen at -21°C.