Measuring 24 h-urine calcium concentration is essential to evaluate calcium metabolism and excretion. Manufacturers recommend acidifying the urine before a measurement to ensure calcium solubility, but the literature offers controversial information on this pre-analytical treatment. The objectives of the study were (1) to compare pre-acidification (during urine collection) versus post-acidification (in the laboratory), and (2) to evaluate the impact of acidification on urinary calcium measurements in a large cohort.
We evaluated the effects of pre- and post-acidification on 24-h urine samples collected from 10 healthy volunteers. We further studied the impact of acidification on the calcium results for 567 urine samples from routine laboratory practice, including 46 hypercalciuria (≥7.5 mmol/24 h) samples.
Calciuria values in healthy volunteers ranged from 0.6 to 12.5 mmol/24 h, and no statistical significance was found between non-acidified, pre-acidified and post-acidified conditions. A comparison of the values (ranging from 0.21 to 29.32 mmol/L) for 567 urine samples before and after acidification indicated 25 samples (4.4%) with analytical differences outside limits of acceptance. The bias observed for these deviant values ranged from −3.07 to 1.32 mmol/L; no patient was re-classified as hypercalciuric after acidification, and three patients with hypercalciuria were classified as normocalciuric after acidification. These three deviant patients represent 6.5% of hypercalciuric patients.
Our results indicate that pre- and post-acidification of urine is not necessary prior to routine calcium analysis.
Darn SM, Sodi R, Ranganath LR, Roberts NB, Duffield JR. Experimental and computer modelling speciation studies of the effect of pH and phosphate on the precipitation of calcium and magnesium salts in urine. Clin Chem Lab Med 2006;44:185–91.
Darn SM, Sodi R, Ranganath LR, Roberts NB, Duffield JR. Experimental and computer modelling speciation studies of the effect of pH and phosphate on the precipitation of calcium and magnesium salts in urine. Clin Chem Lab Med 2006;44:185–91.16475905)| false
Sodi R, Bailey LB, Glaysher J, Allars L, Roberts NB, Marks EM, et al. Acidification and urine calcium: is it a preanalytical necessity? Ann Clin Biochem 2009;46:484–7.10.1258/acb.2009.00902719729500)| false
Vassault A, Hulin A, Chapuzet E, Arnaud J, Giroud C. Membres du sous-groupe 2 analytique de la SFBC [Verification/validation of the performances of analytical method]. Ann Biol Clin (Paris) 2010;68:247–94.
Larcher L, Lefevre G, Bailleul S, Daudon M, Frochot V. Importance of pre-analytical acidification for urinalysis with urinary crystals. Ann Biol Clin (Paris) 2017;75:525–30.
Pratumvinit B, Reesukumal K, Wongkrajang P, Khejonnit V, Klinbua C, Dangneawnoi W. Should acidification of urine be performed before the analysis of calcium, phosphate and magnesium in the presence of crystals? Clin Chim Acta 2013;426:46–50.
Pratumvinit B, Reesukumal K, Wongkrajang P, Khejonnit V, Klinbua C, Dangneawnoi W. Should acidification of urine be performed before the analysis of calcium, phosphate and magnesium in the presence of crystals? Clin Chim Acta 2013;426:46–50.2401282710.1016/j.cca.2013.08.025)| false
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