What is the diagnosis and management for a 7-year-old patient presenting with severe hypocalcemia, acute kidney injury (AKI), polyuria, altered sensorium, and hypokalemia?

Bartter Syndrome: Diagnostic Clue and Management

The clinical presentation of severe hypocalcemia, AKI, polyuria, altered sensorium, and hypokalemia in a 7-year-old strongly suggests Bartter syndrome, particularly Type 1 or Type 2, which are characterized by salt-losing tubulopathy with these exact electrolyte derangements. 1

Key Diagnostic Clues

The constellation of findings points specifically to Bartter syndrome:

• Polyuria with salt wasting is the hallmark of impaired salt reabsorption in the thick ascending limb of Henle's loop 1
• Severe hypokalemia results from increased distal sodium delivery and aldosterone-mediated potassium secretion 1, 2
• Hypocalcemia in this context likely represents severe hypomagnesemia (common in Bartter syndrome), which impairs PTH secretion and causes functional hypocalcemia 1
• Altered sensorium reflects the combined effects of severe electrolyte disturbances, particularly hypocalcemia and hypokalemia affecting neuromuscular function 3
• AKI with polyuria represents the paradoxical combination of volume depletion from salt wasting despite ongoing urinary losses 1

Critical Diagnostic Workup

Immediate laboratory assessment should include:

• Serum electrolytes with particular attention to chloride, magnesium, and calcium (ionized calcium preferred) 1
• Fractional excretion of chloride (typically >0.5% in Bartter syndrome) 1, 2
• Urinary calcium-creatinine ratio to distinguish between types (hypercalciuria suggests Type 1 or 2) 1
• Acid-base status (hypochloremic metabolic alkalosis expected) 1
• Renin and aldosterone levels (hyperreninemic hyperaldosteronism) 1
• Renal ultrasound to detect nephrocalcinosis (typical in Types 1 and 2) 1

Genetic testing with a gene panel should be offered to confirm the diagnosis (SLC12A1 for Type 1, KCNJ1 for Type 2), as this has 90-100% analytical sensitivity in children and guides long-term management 1

Immediate Management Priorities

Acute Stabilization

Severe hypocalcemia requires urgent IV calcium gluconate, particularly given altered sensorium, but monitor ECG closely as hypocalcemia may paradoxically protect against arrhythmias from severe hypokalemia 4, 3

Aggressive potassium chloride replacement is essential:

• Use only potassium chloride (not potassium citrate, which worsens metabolic alkalosis) 5
• Doses of 20-60 mEq/day are frequently required, targeting serum potassium 4.5-5.0 mEq/L 5
• IV replacement may be needed initially given altered sensorium and severity 3

Volume resuscitation with normal saline addresses the volume depletion from salt wasting and provides chloride for bicarbonate excretion 5, 2

Magnesium replacement is critical as hypomagnesemia impairs calcium homeostasis and potassium repletion 1

Chronic Management for Bartter Syndrome

Sodium chloride supplementation (5-10 mmol/kg/day) is the cornerstone of therapy to address the fundamental salt-wasting defect 5, 6

NSAIDs (indomethacin) should be considered for symptomatic patients to inhibit prostaglandin-mediated salt wasting, but must be accompanied by gastric acid suppression 5, 6

Potassium-sparing diuretics (amiloride 2.5-5 mg daily or spironolactone 25-100 mg daily) can help maintain potassium levels, but use cautiously as they may worsen volume depletion despite improving hypokalemia 5, 6

Critical Pitfalls to Avoid

Do not use potassium citrate or other non-chloride potassium salts, as these worsen the metabolic alkalosis that perpetuates potassium wasting 5

Avoid aggressive diuretic therapy - this presentation mimics but is opposite to volume overload conditions requiring diuresis 2

Do not overlook magnesium replacement - hypocalcemia will not correct without addressing concurrent hypomagnesemia 1

Recognize that standard AKI management does not apply - this is volume depletion from salt wasting, not intrinsic renal disease, requiring salt supplementation rather than restriction 1

Differential Considerations

While Bartter syndrome is most likely, briefly consider:

• Diuretic abuse (but unlikely in a 7-year-old) 1, 2
• Gitelman syndrome (but presents later, typically with hypocalciuria rather than hypercalciuria) 1
• Distal renal tubular acidosis (but causes metabolic acidosis, not alkalosis) 6, 7

The combination of young age, polyuria, severe hypokalemia with metabolic alkalosis, and likely hypercalciuria makes Bartter syndrome Types 1 or 2 the definitive diagnosis 1