A simple estimate of glomerular filtration rate in full-term infants during the first year of life

Effect of age and serum creatinine on endogenous digoxin-like substances in infants and children

An apparent digoxin-like immunoreactive substance(s) (DLIS) was evaluated in 374 pediatric patients, 0 to 72 months of age, not receiving digoxin. The relationship between DLIS presence or concentration and age, weight, gender, race, and serum creatinine was investigated. Twenty-seven percent of patients had a positive apparent DLIS concentration (greater than or equal to 0.2 ng/ml). The mean +/- SD concentration of DLIS in the positive group was 0.39 +/- 0.18 ng/ml (range 0.2 to 1.37 ng/ml). Patients in the DLIS-positive group were younger than those in the negative group (P less than 0.01). Although a greater percentage of infants younger than 6 months of age had measurable DLIS, the mean DLIS concentrations, when present, were not significantly different for all age groups (P greater than 0.05). No significant relationship was found between race or gender and DLIS. A weakly positive correlation between serum creatinine concentration and DLIS was noted (r = 0.22, P less than 0.03), but elevated serum creatinine measurements (greater than 0.6 mg/dL) did not correlate with DLIS concentration. These results support the hypothesis that the presence of DLIS is age related, but DLIS appears to be present in a much larger and older population of pediatric patients than previously reported.

Reliability of plasma creatinine measurement in infants and children

Plasma creatinine (Pcr, mg/dl) is often used to estimate glomerular filtration rate (GFR) in children. To establish whether the clinician can rely on the commonly used methods for measuring Pcr, the authors analyzed data from their own modified Technicon Autoanalyzer reference method and compared them to those obtained simultaneously from a Beckman Astra 8 kinetic Jaffe technique or a Technicon continuous flow Jaffe endpoint SMAC method. The SMAC method consistently overestimated Pcr by 0.1 mg/dl, whereas the kinetic method resulted in a large spread around the reference values. Neither laboratory gave consistent results for Pcr below 0.55, the normal range for infants and young children. The SMAC technique tended to underestimate GFR by 20 to 30 percent, whereas the kinetic method resulted in a great deal of scatter (only 37% of the measurements fell within +/- 25% of the values for GFR obtained by the reference method). The results suggest that the subtraction of 0.1 mg/dl from the Pcr measured on the SMAC system would give a value similar to that obtained with the reference method. This correction would permit the use of an estimate of GFR from kL/Pcr, where L is body length in cm and k is a constant (equalling 0.45 in term infants, 0.55 in children, and 0.7 in adolescent boys). The kinetic method requires repetitive determinations of Pcr before any firm conclusions can be drawn about GFR because of the scatter. The reliability of the clinician's laboratory can be tested by sending half the plasma to the laboratory on one day and the other half the next.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple estimate of glomerular filtration rate in low birth weight infants during the first year of life: noninvasive assessment of body composition and growth

The management of the preterm infant often requires rapid assessment of glomerular filtration rate (GFR). We sought to develop a screening test using GFR = kL/Pcr, where GFR is expressed as ml/min/1.73 m2, L is body length in centimeters, Pcr is plasma creatinine concentration, and k is a constant that depends on muscle mass. The value for k in 118 appropriate for gestational age preterm infants (0.34 +/- 0.01 SE) was significantly less than that of full-term infants (0.43 +/- 0.02, P less than 0.001). There was no difference between 12- to 24-hour single-injection inulin clearance and either 0.33 L/Pcr or creatinine clearance in preterm infants. We compared the body habitus of preterm and full-term infants using the assessment of muscle mass from urinary creatinine excretion (UcrV) and from upper arm muscle area (AMA) and volume (AMV), and that of fatness from the sum of five skinfold thickness measurements. During the first year of life, premature infants were found to have a lower percentage of muscle mass than term infants did. On the other hand, they took on a relatively greater amount of subcutaneous fat. There was a very good correlation between AMA or AMV and urinary creatinine excretion (r = 0.91 and 0.94, respectively) in 68 infants with heterogeneous body composition during the first year, indicating the validity of the urinary creatinine measurement. Absolute GFR (ml/min) was also well estimated from AMA or AMV factored by Pcr. We conclude that GFR can be well estimated from 0.33 L/Pcr in preterm infants. The lower value for k reflects the smaller percentage of muscle mass in preterm versus term infants. As a screening test, 1.5 X k or 0.05 L/Pcr predicted low values of GFR with an efficiency of 73%, specificity of 67%, and sensitivity of 88%.

Aztreonam in the treatment of severe urinary tract infections in pediatric patients

Aztreonam was administered to 30 patients, ages 0.03 to 15.4 years, with severe and in 21 cases complicated urinary tract infections caused by members of the family Enterobacteriaceae and Pseudomonas aeruginosa which were resistant to ampicillin and susceptible to the study drug in vitro. A mean dose of 47.7 mg/kg was given intramuscularly every 12 h to 26 patients. In four patients with renal insufficiency, the dose was reduced according to pharmacokinetic data. Permanent urine sterilization and clinical cure were achieved in 22 patients, 13 of whom had urological malformations. In two patients with P. aeruginosa and Proteus mirabilis infections, the treatment failed. Another patient had an Escherichia coli reinfection 21 days after the end of therapy. Four patients with various urological abnormalities had gram-positive superinfections, and two patients had gram-negative superinfections during and at the end of therapy: all six had indwelling ureteric splints or pyelostomy as predisposing conditions. No adverse clinical effects were observed. Some transient and slight or moderate alterations were observed at the end of treatment: eosinophilia (nine cases), elevation of hepatic enzymes (eight cases), prolongation of prothrombin time (three cases), and neutropenia (one case). A pharmacokinetic study was performed in six patients with normal renal function and in seven patients with various degrees of renal insufficiency. The elimination half-life of the drug was inversely correlated with the glomerular filtration rate. At the dosage used, aztreonam proved effective for severe urinary tract infections caused by members of the family Enterobacteriaceae in pediatric patients.

Determination of 51Cr-EDTA clearance in infants by a single capillary blood sample

A method by which 51Cr-EDTA plasma clearance is determined from a single capillary blood sample (Clsc) was studied in 52 children less than 1 year old. The Clsc is calculated as the ratio between the injected dose and the total area under a transformed monoexponential function. The monoexponential curve is determined from the plasma activity 120 min after i.v. single injection of 51Cr-EDTA and a hypothetical initial activity calculated as the injected dose divided by the distribution space of 51Cr-EDTA. The distribution space was estimated from the body surface area. The rate constant of the monoexponential function is transformed by an empirically determined factor to make the area under the curve identical to the area under the true plasma disappearance curve. The Clsc was compared with 51Cr-EDTA plasma clearance (range 18-146 ml/min/1.73 m2) determined by a standard method from five capillary blood samples (Cl). The regression of Cl on Clsc did not differ from the line of identity, the SD being 5.9 ml/min/1.73 m2. In advanced renal failure the one-sample method is very sensitive to inaccuracies in the distribution space estimate and, accordingly, this method should be used only when the clearance value is predicted higher than 30 ml/min/1.73 m2.

Estimation of digoxin dosage in VLBW infants using serum creatinine concentrations

Digoxin steady state plasma concentrations (Css) and the corresponding serum creatinine concentrations were studied in 17 VLBW infants. Birth weight was in the range of 760-1 500 g (mean 1 068 g), gestational age ranged from 26 to 32 weeks (mean 28.7 weeks). Digoxin steady state plasma concentrations were found in the range of 0.5-6.5 ng/ml (mean 1.88 ng/ml) during maintenance therapy with 1.6-8.4 micrograms/kg BW/24 h (mean 4.4 micrograms/kg BW/24 h) given in two divided doses intravenously. No digoxin-like immunoreactive substance could be detected in the plasma of 18 infants (10 patients with a birth weight less than or equal to 1 500 g, 8 patients with a birth weight of 2 100-4 730 g) that were not treated with digoxin. The calculated digoxin clearance ranged from 0.38-4.03 ml/min/kg BW. Serum creatinine concentrations were found in the range of 35-274 mumol/l (0.4-3.1 mg/100 ml). A hyperbolic correlation may be derived from the digoxin clearance and the corresponding serum creatinine concentration. A linear relationship was observed between the dose normalized digoxin concentrations (y = Css/dose in 24 h) and the respective creatinine concentrations x (y = 0.52x-0.05; n = 17; s = 0.24; r = 0.86; p less than 0.01). According to this equation we suggest a dosing schedule for digoxin in VLBW infants with impaired renal function. Digoxin maintenance dose is derived from the digoxin target and the creatinine serum concentration. This dose recommendation proved reliable on four VLBW infants (birth weight 770-1 260 g) with decreased renal function.

Evaluation of renal function and acute renal failure in the neonate

The diagnosis of renal dysfunction in the neonate can be a challenging problem for the practicing pediatrician. Although there are real differences in renal function between term and preterm infants, overall function is quite adequate in both groups when fluid intake and environmental conditions are carefully controlled. When confronted with an infant with a pathologic decrease in urine output, the clinician must provide adequate fluid resuscitation for the infant with prerenal oliguria without inducing fluid overload in the infant with established, intrinsic renal failure. In addition, the infant with obstruction to urine flow must be distinguished. This requires careful assessment of physical findings and a few key laboratory determinations. Once the diagnosis of renal failure is made, frequent clinical monitoring with anticipation of potential complications is critical. Long-term management of renal failure in infancy and intervention for suspected urinary tract malformation in the fetus have emerged as difficult medical and ethical problems as our technology has advanced.

A simple estimate of glomerular filtration rate in adolescent boys

We reexamined the relationship between creatinine clearance (Ccr) and body habitus in 212 girls and 356 boys, including 181 boys and 69 girls between 13 and 21 years of age. The use of formula Ccr = k L/Pcr, where k = 0.55 for the calculation of GFR, resulted in a significant underestimation of GFR in adolescent boys but was suitable for girls. In 51 adolescent boys the equation Ccr = 0.7 L/Pcr resulted in an accurate estimate of GFR. Regression analysis in 133 boys aged 3 to 21 years showed that the constant k increased gradually and linearly with age (r = 0.35, P less than 0.01). GFR could be better estimated for boys of any age by the linear bivariate equation Ccr = 1.5 (age) + 0.5 (L/Pcr), where age is given in years (r = 0.82, P less than 0.001). This equation yielded slightly better results than did 0.7 L/Pcr in 91 additional clearance studies performed in adolescent boys with native kidneys or functioning renal transplants. The larger value for the constant k (0.7) and the age correction for GFR reflect the greater rate of urinary creatine excretion (and thus muscle mass) per unit of body mass in adolescent boys.