None of the published formulae greatly improved the test characteristics beyond simply using the total calcium. A correction formula in widespread use (Payne), quoted in reference texts, agreed less well with ionized calcium than did the unadjusted measured calcium. Correction formulae should be abandoned in favour of the use of uncorrected calcium. In cases of doubt, ionized calcium should be directly measured.
An inception cohort of 107 patients was reviewed to establish the natural history of asymptomatic urolithiasis. With an over-all mean followup of 31.6 months, 73 patients (68.2%) remained asymptomatic and were censored at the time of the last clinical visit. A symptomatic event developed in 34 patients (31.8%). Spontaneous passage occurred in 16 patients (15.0%), endoureteral removal was done in 6 (5.6%), percutaneous nephrostolithotomy was done in 3 (2.8%) and 9 (8.4%) were referred for therapeutic lithotripsy. Cumulative 5-year probability of a symptomatic event developing was 48.5%. A linear association was identified between the development of a symptomatic event and the number of previous stones as well as the number of asymptomatic stones at identification. A significant burden of illness is associated with an expectant strategy as an approach to asymptomatic urolithiasis. Of the patients who had a symptomatic event 47% had spontaneous stone passage, while 26.5% required urological intervention and 26.5% were referred for therapeutic lithotripsy. Prophylactic extracorporeal shock wave lithotripsy, although often advocated, has associated risks and is not always a benign procedure. A randomized controlled trial is required to evaluate properly the role of prophylactic lithotripsy versus an expectant strategy.
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