Measurement of urine relative density using refractometer and reagent strips

The relative density of urine is the ratio of its density to that of water and depends on both the number and weight of solute particles in the sample , while osmolality depends only on the number of solute particles. Water me tabolism is regulated by the interaction of the renal medullary countercurr ent system with the circulating levels of antidiuretic hormone and thirst. The concentration of solids in urine can be measured by weighing, hydrometr y, oscillations of a capillary tube, refractometry and reagent strip. These techniques, interrelated but not identical, are commonly used in hospital laboratories and in clinical wards. We compared the results obtained in 172 5 urine samples of inpatients and outpatients using an automated refractome ter to those obtained using two visually read dip stick tests. The correlat ion coefficients (Super Aution analyser vs. Aution Sticks 10 EA, Aution Sti cks 10 EA vs. N-Multistix, Super Aution analyser vs. N-Multisticks were 0.6 63, 0.645 and 0.514, respectively) and the great dispersion of mountain plo ts demonstrates that different techniques are not interchangeable in the me asurement of relative density. Since the results obtained after discarding the samples with pH higher than 7 and those containing glucose or protein w ere very similar to the ones reported above, the role of these interferents appears negligible in inducing the discrepancy.