24-h urine metabolic profile: is it necessary in all kidney stone formers?

A 24-h urine metabolic profile (24-UMP) is an integral part of nephrolithiasis work-up. We aimed to explore whether it can be waived under certain circumstances.

We reviewed our prospective registry database of patients seen at our outpatient clinic for nephrolithiasis between the years 2010 and 2017. Data included: gender, age at first stone, body mass index (BMI), self-reported comorbidities and family history of nephrolithiasis. A 24-UMP was obtained from each patient under random diet. The following were recorded: urine volume, urinary levels of sodium, calcium, uric acid, oxalate and citrate. Presence of at least one comorbidity (i.e., hypertension/diabetes/hyperlipidemia) was defined as "associated comorbidities" (AC). Their absence was defined as "no comorbidities" (NC). Subjects were divided into two subgroups: first-time and recurrent stone formers, which were further divided into two subgroups: 1st + AC; 1st + NC; recurrent + AC; recurrent + NC. 24-UMPs have been compared between the four groups.

Four hundred and fifty-seven patients were included in the study. In the AC groups, patients demonstrated higher BMI levels (p = 0.001), and were statistically significantly obese (BMI > 30, p = 0.001) and older at first stone event (p = 0.001). First formers, either with AC or NC were more likely to have low urine volume (LUV) compared with recurrent formers (72.5 vs. 59.5%, p = 0.005). In the remaining metabolic abnormalities, no such differences were observed.

First-time stone formers, either with or without AC are likely to demonstrate LUV as their primary metabolic abnormality in 24-UMP. Therefore, 24-UMP may be postponed until recurrent stone event.