Acute pyelonephritis is an acute infection. Today the diagnosis is made primarily on the basis of unspecific clinical symptoms with flank tenderness combined with as a key clue. This study will investigate which clinical and paraclinical characteristics available within 4 hours of hospital stay, that describes the patients admitted in the emergency department with acute pyelonephritis the best.

Acute pyelonephritis (APN) is a severe acute infection in the upper urinary tract, which quite frequently is seen in the emergency department (ED). In our study, we define APN as a urinary tract infection with extension above the bladder, implicated by systemic affection in a suspected urinary tract infection (ie, fever, chills, malaise and/or lethargy beyond normal, signs of sepsis). Most often, an infection of the bladder ascends to the kidneys, causing APN. Symptoms and clinical affection range from mild to severe, but it is always important to recognize and treat APN fast in order to prevent progression to sepsis, renal failure and ultimately death.

The diagnosis APN is primarily made clinically based on symptoms and supported by elevated biomarkers such as C-reactive protein (CRP) and leucocytes, and positive urinary test strips. The diagnostic process can be challenging as there is often weak and atypical symptoms.

The classic symptoms indicating APN is flank tenderness, fever and nausea/vomiting. Typical symptoms of cystitis (dysuria, pollakisuria, suprapubic pain, hematuria) are possible but often absent. Especially elderly can present with more generalized signs of infection with nothing clearly indicating localization to the urinary tract. A positive urine culture verifies the diagnosis, but it is only available after a minimum of 24 hours.

In this study, we seek to identify and quantify the patient characteristics available within 4 hours of hospital stay in patients with APN. The objectives are:

• To identify clinical and paraclinical relevant information available within 4 hours of admission that are associated with APN patients
• To investigate the association between adverse events and clinical and paraclinical relevant information in patients with APN.

Inclusion Criteria:

• Suspicion of APN assessed by the receiving physician.

Exclusion Criteria:

• If the attending physician considers that participation will delay a life-saving treatment or patient needs direct transfer to the intensive care unit.
• Admission within the last 14 days
• Verified COVID-19 disease within 14 days before admission
• Pregnant women
• Severe immunodeficiencies: Primary immunodeficiencies and secondary immunodeficiencies (HIV positive CD4 <200, Patients receiving immunosuppressive treatment (ATC L04A), Corticosteroid treatment (>20 mg/day prednisone or equivalent for >14 days within the last 30 days), Chemotherapy within 30 days)

Acutely admitted patients with suspected APN from three emergency departments in the Region of Southern Denmark (Hospital Sønderjylland, Hospital Lillebælt, Odense University Hospital)