Reference values of renal tubular function tests are dependent on age and kidney function

Area of Science:

• Nephrology
• Clinical Diagnostics

Background:

• Electrolyte disorders from tubular dysfunction are uncommon, with limited validated diagnostic tools.
• Current reference values for tubular function tests are derived from small studies on young, healthy individuals.

Purpose of the Study:

• To evaluate the reliability of four tubular function tests (furosemide, thiazide, furosemide-fludrocortisone, desmopressin) across different age groups and renal function levels.
• To determine if existing reference values are applicable to older adults and patients with compromised kidney function.

Main Methods:

• Four tubular function tests were administered to three groups: young healthy adults (18-50 years), older healthy adults (>50 years), and individuals with compromised renal function.
• Each group comprised 10 participants per test.
• Responses were compared against established reference values.

Main Results:

• Responses in young healthy individuals aligned with existing literature.
• Reduced fractional chloride excretion post-furosemide and thiazide was observed in older adults and those with kidney impairment compared to young adults.
• Maximal urine osmolality after desmopressin was significantly lower in older adults and patients with compromised renal function.

Conclusions:

• Established reference values for tubular function tests in young, healthy adults cannot be directly extrapolated to older individuals or those with compromised kidney function.
• There is a need for larger validation studies to establish accurate reference values for these specific patient groups.