Urinary infections in children is very common. Delay in the diagnosis may be followed by complications.

Pyelonephritis is a febrile urinary infection with a renal injury. In local experience, about 30-40% of the children don't have an inflammatory syndrome or echographical abnormalities. Do they really have a renal injury ? In fact, only the scintigraphy or the Magnetic Resonance Imaging (MRI) may show these lesions, but are done only in specific cases (diagnosis of uropathy or nephropathy). Recent studies have shown that plasmatic Neutrophil Gelatinase-Associated Lipocalin (NGAL) is associated traumatic or inflammatory renal lesions. But the plasmatic NGAL cutoff is fluctuant depending on the cohorts and gold standards. The main goal is to evaluate a new methodology of dosing NGAL, (immuno-dosage turbidimetric dosage). The investigators suppose that plasmatic NGAL protein will detect renal injury, which would be confirmed by MRI.

The aim of this study is to evaluate the area under the curve (AUC) of plasmatic NGAL protein with an automatised method, for the detection of renal injury. This would be confirmed by reno vesical MRI, in children over 2 years old with febrile urinary infections

Urinary infections in children is very common and should be diagnosed as soon as possible. Delay in the diagnosis ma be followed by complications such as sepsis, renal scar, high blood pressure, renal insufficiency.

The diagnosis may be tough when it comes to children because of its unspecific symptomatology. Pyelonephritis is a febrile urinary infection associated to renal abnormalities. Following the french recommendations ("Sociéte de Pathologie Infectieuse de Langue Française" The French Society of Infectious disease SPILF and "Groupe de Pathologies Infectieuses Pédiatriques" The Pediatric infectious disease Group GPIP 2015), the investigators should first use an intravenous probabilistic antibiotic during minimum 48 hours to lower the bacterial inoculum. Then, the investigators should switch to an oral antibiotic during 8 days to sterilise the urines.

In local experience, about 30 to 40 % of the children don't have an inflammatory syndrom or echographical abnormalities. Do they really have a renal injury? In fact, only the scintigraphy or the Magnetic Resonance Imaging (MRI) may show these lesions, but are done only in specific cases (diagnosis of uropathy or nephropathy). Recent studies have shown that plasmatic Neutrophil Gelatinase-Associated Lipocalin (NGAL) is associated traumatic or inflammatory renal lesions. But the plasmatic NGAL cutoff is fluctuant depending on the cohorts and gold standards. In those studies, dosing NGAL was non automatised and long.

the investigators would like to evaluate a new methodology of dosing NGAL, (immuno-dosage turbidimetric dosage). The investigators suppose that plasmatic NGAL protein will detect renal injury, which would be confirmed by MRI.

This is an interventional, prospective, multicentered study. It will last for 2 years. The aim of this study is to evaluate the AUC of plasmatic NGAL protein with an automatised method, for the detection of renal injury. This would be confirmed by reno vesical MRI, in children over 2 years old with febrile urinary infections.

Inclusion Criteria:

• Children over 4 years old, continent
• Fever ≥ 38,5 degrés Celsius for less than 4 days
• Positive urine strip
• Parental authorisation
• Using french Health Care System

Exclusion Criteria:

• Uropathy
• 2nd febrile urinary infection
• No parental authorisation
• Non confirmed Urinary infection on a well done Cyto Bacteriological Urine (CBU)
• Urinal contamination defined by : ≥ 2 bacterial, urinal bacteriuria < 10^5 Colony Forming Unit (CFU)/ml