Wilms tumour (nephroblastoma) is the most important malignant cause of haematuria in children — it is the most common renal tumour in childhood, occurring predominantly between ages 3-4 years (range 1-8 years). The classic presentation is an abdominal mass discovered incidentally by a parent or during examination, often with haematuria. The cardinal rule: do not repeatedly palpate the abdomen if Wilms tumour is suspected — the tumour has a fibrous capsule that can rupture with vigorous palpation, causing intraperitoneal bleeding and tumour dissemination. After a single careful examination that identifies an abdominal mass, refer urgently without further abdominal palpation and document the finding. Prognosis for Wilms tumour is excellent with modern treatment (surgery + chemotherapy ± radiotherapy for high-stage disease) — 5-year survival exceeds 90% for localised disease. Early identification is the key GP contribution.

The acanthocyte test is the most specific microscopic finding for glomerular haematuria — acanthocytes are red blood cells with irregular membrane protrusions ('blebs' or 'spicules') that form as the cells are squeezed through damaged glomerular basement membrane. They are best seen on phase-contrast microscopy; on standard light microscopy they appear as ring-shaped or crenated cells. A count of more than 5% acanthocytes among the urinary RBCs has a sensitivity of approximately 50% and specificity of approximately 98% for glomerular disease. The presence of RBC casts is even more specific — these are red cells embedded in a Tamm-Horsfall protein matrix that forms in the renal tubules, confirming that the bleeding is intra-glomerular. Dipstick haematuria with visible acanthocytes or RBC casts on urine microscopy is a strong indication for urgent nephrology referral. GPs should request urine microscopy (not just dipstick or culture) when glomerular haematuria is suspected.

The urine protein:creatinine ratio (uPCR) is the most clinically useful quantification of proteinuria in children — it correlates well with 24-hour urine protein excretion and is far more practical than a timed urine collection. The interpretation: uPCR below 20 mg/mmol is normal; uPCR 20-100 mg/mmol is mildly elevated (monitor); uPCR above 100 mg/mmol is significant proteinuria requiring investigation; uPCR above 200 mg/mmol is heavy proteinuria (nephrotic range approaching). Haematuria with significant proteinuria (uPCR above 100) almost always indicates glomerular pathology and requires nephrology referral. Isolated haematuria (without proteinuria, hypertension, or renal impairment) has a much broader differential and more benign prognosis — thin basement membrane disease, IgA nephropathy (mild), exercise-induced, or benign familial haematuria. The combination of haematuria + proteinuria is the most important investigation result in paediatric haematuria assessment.

Hypercalciuria is the most common cause of persistent isolated microscopic haematuria in children in the absence of proteinuria or renal impairment — it is found in approximately 30-35% of children with isolated microscopic haematuria when properly investigated. The mechanism: excess urinary calcium crystallises in the tubules and collecting system, causing microtrauma to the urothelium and red cell leak. The diagnosis: spot urine calcium:creatinine ratio above 0.7 mmol/mmol (in children under 7); above 0.5 mmol/mmol (children over 7). Confirmed hypercalciuria on two samples with no other cause of haematuria: dietary calcium restriction is NOT recommended (risks bone density effects); dietary sodium restriction (reduces urinary calcium); adequate fluid intake; thiazide diuretics (chlorothiazide or hydrochlorothiazide) for recurrent calcium stones or symptomatic hypercalciuria — reduces urinary calcium excretion. Paediatric nephrology referral for stone-forming hypercalciuria or persistent unexplained haematuria.

The isolated asymptomatic microscopic haematuria management pathway in children is defined by NICE and the British Association of Paediatric Nephrology — it requires structured investigation and long-term follow-up rather than immediate nephrology referral. The BAPN guideline recommends: confirm haematuria on two separate urine samples at least 2 weeks apart (to exclude transient causes — exercise, menstruation, minor UTI); if confirmed persistent, investigate with renal USS + uPCR + BP + renal function; if all investigations are normal: annual GP review (BP + uPCR + renal function + urine dipstick) is sufficient. The key safety-net: escalate to paediatric nephrology if at any annual review the child develops proteinuria (uPCR rising above 20 mg/mmol), hypertension, or renal impairment — these features convert 'isolated microscopic haematuria' into 'glomerulonephritis' and require biopsy.

IgA nephropathy (Berger's disease) management in children has evolved significantly with the TESTING trial (2022) and STOP-IgAN trial data — the key finding is that ACE inhibitors/ARBs (ramipril or losartan) are the cornerstone of treatment for IgA nephropathy with proteinuria, providing both antiproteinuric and nephroprotective effects independent of blood pressure reduction. NICE guidance recommends ACE inhibitors for children with IgA nephropathy and uPCR above 50 mg/mmol. The TESTING-reduced trial showed that low-dose prednisolone (0.4 mg/kg/day for 6 months) combined with supportive care reduced the risk of ESRD by approximately 50% compared to supportive care alone in adults with proteinuric IgA nephropathy. For children with significant IgA nephropathy: paediatric nephrology management with ACE inhibitor ± low-dose prednisolone is the current standard. Sparsentan (dual endothelin/angiotensin receptor antagonist) was approved by FDA in 2023 for IgA nephropathy — UK NICE appraisal pending.

The testicular involvement in HSP deserves explicit mention because testicular torsion can complicate HSP and presents a surgical emergency — the vasculitis of HSP can affect the small vessels of the testes, causing scrotal pain and swelling that can be confused with epididymo-orchitis. However, HSP-associated scrotal pain may also indicate true testicular torsion (which occurs at the same age group as HSP — school-age boys). Any HSP patient presenting with scrotal pain must have testicular torsion excluded urgently — USS of the testes + surgical opinion within 4-6 hours (the window for viable salvage of a torted testis). A 'wait and see' approach to scrotal pain in any male of any age is never acceptable if torsion cannot be excluded clinically.

The early ACE inhibitor therapy in Alport syndrome is one of the strongest evidence-based preventive interventions in paediatric nephrology — the Alport Syndrome Treatment and Outcome Registry (ATOSMART) and subsequent studies consistently show that starting ACE inhibitor therapy (ramipril 0.05-0.1 mg/kg/day) in boys with Alport syndrome before the onset of proteinuria significantly delays the onset of ESRD by an average of 10-13 years compared to treatment started after proteinuria develops. The mechanism: GFR loss in Alport syndrome is driven by glomerular hypertension from the abnormal GBM, and ACE inhibitor-mediated reduction in intraglomerular pressure provides nephroprotection. GPs who identify persistent microscopic haematuria in a boy with a family history of hearing loss, haematuria, or renal failure should have a very low threshold for referral to paediatric nephrology — early diagnosis and early ACE inhibitor therapy can preserve renal function for decades.

The annual follow-up of isolated asymptomatic microscopic haematuria in children is a long-term commitment that requires proactive recall and documentation — many children with 'benign' isolated haematuria (thin basement membrane disease, mild IgA nephropathy, hypercalciuria) will never develop clinical problems, but approximately 15-20% will develop proteinuria, hypertension, or renal impairment over the following years. The GP's role is to maintain a safety net: a child who was labelled 'isolated microscopic haematuria — benign' at age 8 and never reviewed again, who presents at age 22 with stage 3 CKD, represents a missed opportunity for ACE inhibitor nephroprotection. The recall system should be integrated into the practice's chronic disease register or coded appropriately (ICD code R31 — haematuria) to ensure the annual check is flagged. If the GP practice does not have a recall system for paediatric haematuria, the referral letter to community paediatrics should specify the monitoring requirements.