I found the article by Park et al. [1], "Relationship between spontaneous passage rates of ureteral stones less than 8 mm and serum C-reactive protein levels and neutrophil percentages," which was recently published in your very valuable journal, very interesting. The authors concluded that when the serum C-reactive protein (CRP) level and neutrophil percentage of a patient are high, aggressive treatment such as extracorporeal shock wave lithotripsy should be considered.

CRP is an acute phase protein that is raised in inflammatory conditions. Risk of early sepsis or occult sepsis is present if CRP is elevated (>28 mg/L) in patients with ureteric stones [2]. Urinary diversion either by placement of a ureteral stent or by percutaneous nephrostomy followed by ureteroscopy or shock wave lithotripsy will be a safer option than aggressive treatment with shock wave lithotripsy.

There is no defined cutoff level of CRP in the literature that predicts spontaneous passage of a ureteric stone. However, Aldaqadossi [3] used receiver operator characteristic curves to determine a CRP cutoff of 28 mg/L for prediction of spontaneous ureteric stone expulsion with a sensitivity of 75.8% and a specificity of 88.9%. In the study by Park et al. [1], the CRP level division was different from the cutoffs previously described, and the reason for this difference was not very clear.

Lastly, stone size was the most predictive factor for spontaneous passage of ureteric stones in many studies [4,5]. Interestingly, this was not seen in the study by Park et al. [1] (Table 3). It would be interesting to know the reason behind this.