Ultrasound is an effective and noninvasive method of evaluating renal swelling in infants with their first urinary tract infection

Low agreement between kidney volume and kidney length z-scores

BACKGROUND

Pediatric nephrologists use kidney length and kidney volume z-scores to longitudinally assess normal nephron endowment. However, most radiologists only report kidney length. Agreement between kidney length and kidney volume z-scores in children has been understudied. This study aims to assess agreement between kidney length and kidney volume z-scores in children.

METHODS

This novel cross-sectional cohort study prospectively followed prematurely born babies from a large specialized prematurity follow-up center. A healthy control group matched the cases by age and sex and was recruited from schools. Children were assessed for kidney length and kidney volumes at age 5 by three independent ultrasonographers. All measurements were performed in triplicate. Detailed anthropometry, blood pressure, and kidney function were also obtained. Age-independent z-scores were calculated for all parameters according to Scholbach and Weitzel and compared using descriptive statistics.

RESULTS

We studied 89 premature patients (median 32 weeks gestational age) and 33 healthy controls (median 38 weeks gestational age). There were 732 determinations of kidney length, width, and thickness. The mean z-score of the right kidney length was 0.65 ± 0.08 (SEM) compared with 0.88 ± 0.08 of the left kidney length (p = 0.0003, two-sided paired t test). The squared correlation coefficient for kidney volume to kidney length was 0.32 (p < 0.0001). Bland and Altman analysis revealed considerable bias with - 1.36 ± 0.76 standard deviations and 95% limits of agreement from - 2.83 to - 0.16.

CONCLUSION

Reporting only kidney length results in significant overestimation of age-independent z-scores. Based on our findings, consideration to measuring all kidney dimensions may be more appropriate.

Renal swelling indicates renal damage in infants with their first urinary tract infection

AIM

We used ultrasound to evaluate renal swelling as a predictor of acute and permanent renal damage in infants with their first urinary tract infection (UTI).

METHODS

The cohort at the Queen Silvia Children's Hospital, Gothenburg, Sweden, comprised 101 infants with their first UTI at a mean age of 3.9 ± 3.0 months. Acute and follow-up ultrasounds were carried out a few days and one month after treatment started, and a ^99m technetium dimercaptosuccinic acid (DMSA) scan was carried out after one month and after a year if the first scan was abnormal.

RESULTS

The acute ultrasounds showed that renal length and volume, calculated as standard deviation scores (SDS), were 1.39 ± 1.43 SDS and 1.30 ± 1.08 SDS. We found that 52% of the one-month DMSA scans and 25% of the one-year DMSA scans were abnormal. Renal length (p = 0.0026) and initial volume (p = 0.0005) on the ultrasound predicted acute renal damage at the one-month DMSA scan and initial renal length (p = 0.030) predicted permanent renal damage at the one-year DMSA scan.

CONCLUSION

Renal swelling was associated with renal damage. Although the diagnostic performance compared with the DMSA scan was weak, renal swelling may help clinicians to make decisions about further investigations and follow-ups of infants with UTIs.