In order to include measurements of children with normal serum creatinine level only, several steps of exclusion were carried out. Firstly, to prevent the influence of serial measurements, we randomly selected one assay per patient. Secondly, all determinations requested by the departments of Paediatric Nephrology, Paediatric Oncology and the Neonatal and Paediatric Intensive Care Units were excluded. Thirdly, the remaining patients were screened for pathophysiological conditions that could cause renal damage (Table 2 ).
Patients born preterm (<37 weeks of gestational age) or small for gestational age (birth weight <10th percentile according to The Netherlands Perinatal Registry 2007 [13 ]) were excluded because of their expected immature renal function. All patients with a proven or suspected syndrome were also excluded, for many syndromes are associated with multiple organ anomalies, including renal pathology. Finally, during measurement on the Hitachi 912, those indices possibly associated with interference with the enzymatic method (hyperbilirubinaemia, hypertriglyceridaemia and haemolysis) were measured in each sample. Samples with indications of haemolysis, hyperbilirubinaemia or hypertriglyceridaemia were excluded. All patients with muscle disease were also excluded.
All assay results from 1- to 7-day-old children were included in view of the expected rapid initial decline in serum creatinine during the first days of life. For older children up to 3 months of age, 15 random determinations per week were included; for those between 3 and 12 months, five random determinations per week.
The exclusion procedure was carried out by two physicians who were blinded to the serum creatinine levels.
Exclusion criteria and the method of exclusion
Exclusion criterion | Method of exclusion | na |
---|---|---|
Kidney disease | Exclude all cases with kidney disease described in medical record | 62 |
Use of cytostatic drugs | Exclude all patients receiving cytostatic drugs or with proven malignancy described in medical record | 12 |
Premature | Exclude all patients with gestational age <37 weeks described in medical record | 224 |
Small for gestational age | Exclude all cases if birth weight was: - <2300 g if gestational age = 37 weeks - <2500 g if gestational age = 38 weeks - <2700 g if gestational age = 39 weeks - <2900 g if gestational age = 40 weeks - <3000 g if gestational age = 41 weeks - < 3100 g if gestational age = 42 weeks | 64 |
Muscle disease | Exclude all patients with muscle disease described in medical record | 1 |
Haemolysis | Exclude all patients with proven haemolysis described in medical record or found in laboratory tests | 0 |
Hyperbilirubinaemia | Exclude all patients with hyperbilirubinaemia proven with laboratory test | 32 |
Hypertriglyceridaemia | Exclude all patients with hypertriglyceridaemia proven with laboratory test | 2 |
Syndromes | Exclude all patients with a syndrome described in medical record. Exclude all patients with multiple congenital dysmorphisms described in medical record | 79 |
After major surgery | Exclude all determinations performed after (cardio)thoracic surgery or extensive abdominal surgical procedure described in medical record | 128 |
Prerenal problems | Exclude all patients with shock, dehydration, heart failure or cardiopulmonary resuscitation described in medical record | 131 |
Urological problems | Exclude all patients with hydronephrosis, vesicoureteral reflux, urinary tract infection described in medical record | 128 |
aThe total number of exclusions is >748 because some patients were excluded for more than one reason
All assay results from 1- to 7-day-old children were included in view of the expected rapid initial decline in serum creatinine during the first days of life. For older children up to 3 months of age, 15 random determinations per week were included; for those between 3 and 12 months, five random determinations per week.
The exclusion procedure was carried out by two physicians who were blinded to the serum creatinine levels.