determination of renal length and volume through ultrasound scanning in newborn infants considered normal according to who criteria. a descriptive, observational, cross-sectional study and literature review

Introduction: Renal mass and glomerular number correlate significantly in infants under the age of 3 months and in normal adults, but both of them can only be measured ex vivo. On the other hand, renal volume (RV), also proportional to renal mass, can be calculated through ultrasound scanning, an alternative to estimate glomerular number in vivo. Renal volume is determined by means of a formula which includes three diameter measurements: longitudinal (LD), anteroposterior (APD) and transverse (TD). Objetives: To determine TD, LD, APD and renal volume, and to establish the relation between these diameters and anthropometric measurements in neonates (within the first 48 hours after birth), considered to be normal according to WHO criteria. The study was performed in the city of Resistencia, province of Chaco, Argentina. Methods: A descriptive, observational, cross-sectional, non-probability sampling study was conducted on 27 male and female neonates, who were healthy during the perinatal and neonatal periods. Ultrasound scanning was performed by an imaging expert while both the mother and the newborn infant (NI) were still hospitalized. Results: The LD was 48.3 mm in the right kidney (RK) and 48.1 mm in the left kidney (LK). The total renal volume (TRV) was 23.3 ± 4.8 mL. The mean kidney measurements were 4.2 cm x 2.3 cm x 2.2 cm. A correlation with weight, height and body surface area (BSA) was found only in the TD of both kidneys (p < 0.01). Conclusions: The diameters and the RV values measured during the study are within the ranges described in the reviewed literature. The TD was correlated with weight, height and BSA. The shape of neonates’ kidneys is different than that of older children and adults, suggesting that another formula, such as the elliptic cylinder equation instead of the ellipsoid or Dinkel’s formula, should be used for this age group.