Introduction
We investigated the effects of acidification and storage on calcium recovery in spot urine samples.
Methods
In a retrospective study, 43 spot urine samples from patients with metabolic bone disease, which had been previously analysed fresh for calcium and creatinine, were acidified and incubated for 2 h at room temperature and re-analysed. In a prospective study, fresh spot urine samples from 15 volunteers were split into two aliquots - one left unacidified and the other acidified with 6 mol/L HCl to pH< 2. Both aliquots were analysed immediately and after storage at 4°C for 24 h.
Results
In both studies, the calcium creatinine ratios obtained on acidified and non-acidified spot urine samples were not different, both when measured immediately as well as after storage at 4°C for 24 h.
Conclusions
The acidification of spot urine samples would thus appear to be unnecessary for calcium/creatinine measurements in metabolic bone disease if they were undertaken within at least 24 h.
