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Kidney Week

Abstract: PO1127

Missing the Obvious? A Story of Salt, Water, and Unexplained Hyperkalemia

Session Information

Category: Fluid, Electrolyte, and Acid-Base Disorders

  • 902 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Authors

  • Spring, Aaron M., The Hospital for Sick Children Department of Paediatrics, Toronto, Ontario, Canada
  • Lemaire, Mathieu, The Hospital for Sick Children Department of Paediatrics, Toronto, Ontario, Canada
Introduction

Most clinicians are familiar with the differential diagnosis of hyperkalemia, from pseudohyperkalemia to rare tubulopathies. Herein, we describe three patients with years-long histories of unexplained hyperkalemia despite extensive investigations (details in Table 1). While all achieved normokalemia with various prescription regimens, the underlying etiology remained elusive. We suggest that all cases were likely due to chronic, mild hypovolemia in the context of self-imposed dietary salt restriction.

Case Description

Patient A: A 6-week-old girl with persistent hyperkalemia and very low urine Na+. Normokalemia was achieved with hydrochlorothiazide and dietary K+ restriction but maintained with optimized fluid and Na+ intake alone.
Patient B: An 11-year-old boy with spastic cerebral palsy with persistent hyperkalemia after a mild AKI attributed to rhabdomyolysis. Serum K+ improved with sodium polystyrene (SPS) and dietary K+ restriction; it normalized after IV saline infusion, while NPO.
Patient C: A 5-month-old boy with Stüve-Wiedemann Syndrome and feeding difficulties with persistent hyperkalemia that normalized on SPS. After G-tube insertion at 2 years, K+ remained normal despite stopping the SPS due to improved fluid and Na+ intake.

Discussion

It has long been established that adequate Na+ and fluid delivery to distal nephrons is necessary for optimal K+ handling. It is therefore surprising to find almost no mention of Na+-responsive hyperkalemia in the literature for children beyond the neonatal period. Our patients all had hyperkalemia in the context of normonatremia, but very low fractional excretion of Na+ (FeNa) and low trans-tubular K+ gradient (TTKG). They all remained normokalemic when salt and water intake was optimized, despite stopping their hyperkalemic prescriptions. Careful, early consideration of low distal Na+ and water delivery as a cause for unexplained hyperkalemia could prevent extensive workups and unnecessary prescriptions.

Relevant investigations
PatientsTime pointsSerum values (mmol/L)Serum creat (μmol/L)Urine values (mmol/L)TTKGFeNa (%)
K+Na+OsmTotal CO2K+Na+Osm
A6 wk7.0 ↑ (a)140298213528<201786.7N/A
10 y5.1 ↑ (b)143305 ↑ (d)23467619210884.20.4
BPre-tube5.5 ↑ (b)144 ↑ (c)301 ↑ (d)294242548762.60.07
Post-tube3.6 ↓ (b)151 ↑ (c)308 ↑ (d)N/A34383309753.30.6
C5 mo5.9 ↑ (a)137284221314<201255.4N/A
2 y4.713628026231341898779.10.7

Normal ranges: a: 3.5-5.6 mmol/L (mEq/L), b: 3.7-5.0 mmol/L (mEq/L), c: 135-143 mmol/L (mEq/L), d: 282-300 mmol/L (mOsm/kg H2O)