Urinalysis, renal function and paediatric kidney assessment — branching viva

Station map

Branch A — Well child, calculate the eGFR

Examiner: A 7-year-old is 120 cm tall with a serum creatinine of 0.7 mg per dL on an enzymatic assay. Calculate the estimated GFR and stage it. [1]

Strong answer should include:

• State the bedside Schwartz equation: eGFR equals 0.413 times height in cm divided by serum creatinine in mg per dL. [1]
• Arithmetic: 0.413 times 120 divided by 0.7, about 71 mL per min per 1.73 m2. [1]
• Stage G2 (60 to 89) per KDIGO; note the value is indexed to 1.73 m2. [4]
• Mention the need for a measured height and the original 0.55 constant being outdated. [1]

Trap: quoting the original 0.55 constant or forgetting to index to 1.73 m2. [1]

Branch B — Febrile toddler with a bag culture

Examiner: An 18-month-old is febrile. The bag-urine culture grows mixed coliforms. Can you treat for urinary tract infection? [3]

Strong answer should include:

• Bag urine has a high contamination rate; mixed growth usually means skin flora. [3]
• Use clean-catch, catheterisation or suprapubic aspiration for diagnosis. [3]
• A reliable-method culture at a significant count with a single organism supports infection. [3]
• Read dipstick and culture with the clinical picture; a sick febrile child with a weak dipstick still needs a reliable sample. [2]

Trap: treating a contaminated bag culture as disease and creating false diagnostic momentum. [3]

Branch C — Oliguric child, normal creatinine

Examiner: A dehydrated, oliguric 4-year-old has a creatinine within the reference range. The night team plans discharge because the kidneys are fine. [5]

Strong answer should include:

• Creatinine lags the fall in filtration; a single normal value does not exclude acute kidney injury. [5]
• Trend the creatinine and the urine output; manage fluid, electrolytes and the cause. [5]
• Add the urinalysis and microscopy to localise intrinsic versus pre-renal disease. [2]
• Escalate to nephrology and intensive care if oliguria or potassium climb persist. [4]

Trap: equating one normal number with normal function in a sick child. [5]

Branch D — Adolescent at transition

Examiner: A 17-year-old with stable chronic kidney disease transfers to adult care. The paediatric Schwartz equation is being used. What should change? [6]

Strong answer should include:

• Agree the equation with the adult team to avoid a jump in the GFR estimate at handover. [6]
• The Full Age Spectrum or cystatin C-based equations cross the boundary more smoothly. [6]
• Hand over the trend and the baseline, not only single numbers. [4]
• Confirm reference intervals used by the adult laboratory. [4]

Trap: carrying a paediatric equation into adult care without confirming continuity. [6]

Closing synthesis the candidate should say

"I collect urine by a method I can trust, read the dipstick against the microscopy, estimate GFR with the bedside Schwartz equation using the 0.413 constant and a measured height, stage with KDIGO, and trend the creatinine. I never let a normal creatinine or a contaminated culture end a high-risk story." [1] [2] [5]