Immediate evaluation

1. Assess severity first

• Full vital signs, especially blood pressure using the correct pediatric cuff and percentile chart
• Weight, edema, fluid balance, urine output
• Look for facial/leg swelling, rash or purpura on legs/buttocks, joint or abdominal pain, sore throat/skin infection, flank pain, dysuria, diarrhea, bruising, jaundice
• Review the exact antibiotic name, dose, start date, and any NSAID use such as ibuprofen

2. Repeat and properly characterize urine

• Urine dipstick and microscopy: RBC count, dysmorphic RBCs, RBC casts, WBCs, WBC casts, bacteria/crystals
• Urine culture before changing antibiotics, if UTI is possible
• First-morning urine protein:creatinine ratio or albumin:creatinine ratio to quantify protein loss. KDIGO advises first-morning protein-creatinine testing in children rather than relying on 24-hour collection. KDIGO pediatric guidance

3. Blood tests

• CBC with platelet count and peripheral smear
• Serum creatinine, urea/BUN, electrolytes, bicarbonate, calcium, phosphate, albumin
• CRP/ESR as clinically indicated
• C3 and C4 complement
• Streptococcal evidence if compatible history: ASO and anti-DNase B titers, throat/skin testing as indicated
• If atypical or severe: ANA, anti-dsDNA, ANCA, serum IgA, hepatitis testing and other tests guided by pediatric nephrology
• If diarrhea, pallor, thrombocytopenia, or AKI: assess urgently for hemolytic uremic syndrome

4. Imaging

• Renal and bladder ultrasound if gross hematuria, flank pain, suspected stone/obstruction, recurrent UTI, AKI, or uncertainty about the cause.
• A biopsy is not routine for typical post-infectious GN, but may be needed when features are atypical, kidney function worsens, complement remains low, hypertension persists, or proteinuria is heavy. Gross hematuria, low C3, acute kidney injury, sustained hypertension, rash, or arthritis are atypical features that warrant nephrology input. KDIGO guidance

Treatment principles

If acute nephritic syndrome/post-infectious GN is suspected

• Urgent pediatric/nephrology consultation
• Monitor BP, urine output, daily weight, creatinine, potassium, and fluid balance.
• Restrict salt. Fluid restriction may be required if edema, hypertension, oliguria, or reduced kidney function.
• Treat hypertension and fluid overload in hospital, commonly with a loop diuretic and, if necessary, antihypertensive therapy chosen by the clinician.
• Treat a documented active streptococcal infection with an appropriate antibiotic, but this does not immediately reverse the kidney inflammation.
• Avoid nephrotoxins, especially NSAIDs and unnecessary contrast. Dose-adjust all medicines to renal function.

If drug-induced acute interstitial nephritis is plausible

• The prescribing clinician should urgently review the antibiotic.
• Stop the suspected drug only under medical direction, especially if it is being used for a serious infection.
• Check creatinine, eosinophils, urinalysis/culture, and consider nephrology. Treatment begins with withdrawal of the causative medicine; corticosteroids are sometimes considered by specialists if renal injury is significant or not improving. Goldman-Cecil Medicine, “Acute Interstitial Nephritis”.

If UTI/pyelonephritis is confirmed

• Use urine culture and sensitivity to guide an antibiotic, then reassess for structural abnormality or nephrology/urology referral if hematuria/proteinuria persists. UTI alone may cause hematuria, but significant proteinuria or RBC casts should prompt evaluation for glomerular disease.

Referral/admission triggers

• Hypertension
• Oliguria/anuria or rising creatinine
• Edema, pulmonary symptoms, or fluid overload
• Hyperkalemia, acidosis, or severe vomiting
• Gross hematuria with clots or severe pain
• RBC casts, substantial proteinuria, low albumin, or nephrotic-range proteinuria
• Purpuric rash, abdominal pain, joint pain, thrombocytopenia, anemia, or diarrhea
• Persistent fever or concern for sepsis