Evidence-Based Supplement & Herb Guides

Fluid Balance Urine Test Panel: Osmolality, Sodium, Creatinine, and Hydration Status

Understand how urine osmolality, sodium, and creatinine work together to assess hydration, kidney concentration, hyponatremia, polyuria, and fluid balance.

A fluid balance urine test panel combines urine osmolality, sodium, and creatinine to show how the kidneys are concentrating urine and handling water and...

Fractional Excretion of Potassium (FEK) Test: Potassium Balance and Kidney Loss

$Learn how fractional excretion of potassium (FEK) is calculated and interpreted for kidney potassium loss, hypokalemia, hyperkalemia, and aldosterone-related disorders.$

The fractional excretion of potassium (FEK) estimates what percentage of the potassium filtered by the kidneys is ultimately excreted in urine. It is calculated...

Fractional Excretion of Sodium (FENa) Test: Acute Kidney Injury and Volume Status

Learn how FENa is calculated, what values below 1% or above 2% can mean, when diuretics and CKD make it unreliable, and how it fits into acute kidney injury evaluation.

Fractional excretion of sodium (FENa) estimates the percentage of filtered sodium that the kidneys excrete in urine. It is calculated from paired urine and...

Fractional Excretion of Urea (FEUrea) Test: Kidney Injury, Diuretics, and Prerenal AKI

Understand how FEUrea is calculated, what the 35% cutoff means, why diuretics complicate AKI testing, and how FEUrea compares with FENa for prerenal and intrinsic kidney injury.

Fractional excretion of urea (FEUrea, also written FEU or FEUN) estimates the percentage of filtered urea that is excreted in urine. Clinicians mainly use...

Fractional Excretion of Uric Acid (FEUA) Test: Gout, Kidney Handling, and Uric Acid Disorders

Learn how FEUA measures kidney uric acid handling, what high and low values can mean in gout, hypouricemia and SIAD, and which medications and kidney conditions affect the result.

Fractional excretion of uric acid (FEUA) estimates what percentage of urate filtered by the kidneys is excreted in urine. It combines paired blood and...

Transtubular Potassium Gradient (TTKG) Test: Potassium Disorders and Aldosterone Effect

Learn how TTKG is calculated, what low and high values traditionally mean in potassium disorders, why aldosterone affects the result, and why modern clinicians interpret TTKG cautiously.

The transtubular potassium gradient (TTKG) is a calculated urine index historically used to estimate potassium secretion in the cortical collecting duct and to judge...

Urine Ammonium Test: Kidney Acid Excretion and Metabolic Acidosis Evaluation

Learn how urine ammonium measures kidney acid excretion, why low levels matter in renal tubular acidosis and CKD, and how direct NH₄⁺ testing compares with the urine anion and osmolal gaps.

A urine ammonium test measures ammonium (NH₄⁺), the major form in which the kidneys excrete daily acid. It is most useful when blood tests...

Urine Anion Gap Test: Metabolic Acidosis, Kidney Acid Excretion, and Meaning

Learn how to calculate the urine anion gap, what negative and positive values can mean in normal-anion-gap metabolic acidosis, and why direct urine ammonium is often preferred.

The urine anion gap (UAG) is a calculated value used mainly during normal-anion-gap metabolic acidosis to estimate whether the kidneys are increasing ammonium excretion....

Urine Calcium Test: High, Low, Kidney Stones, Parathyroid Causes, and Meaning

Urine calcium testing helps evaluate hypercalciuria, low urine calcium, kidney stone risk, and parathyroid disorders. Learn 24-hour ranges, causes, and next steps.

A urine calcium test measures how much calcium is being excreted by the kidneys. It is most often used to evaluate recurrent kidney stones,...

Urine Chloride Test: High, Low, Acid-Base Balance, and Volume Status

Understand urine chloride test results, including low and high values, metabolic alkalosis, vomiting, diuretics, volume status, and 24-hour testing.

A urine chloride test measures how much chloride, a major negatively charged electrolyte, is being excreted in urine. The result is most useful when...

Urine Citrate Test: Kidney Stone Risk, Low Citrate, and Urine Chemistry

Learn what a urine citrate test shows, why low citrate raises kidney stone risk, common causes of hypocitraturia, and how diet and potassium citrate affect results.

A urine citrate test measures citrate excreted by the kidneys, usually as part of a 24-hour urine evaluation for kidney stones. Citrate is protective...

Urine Creatinine Test: Kidney Function, Collection Check, Ratio Tests, and Meaning

Learn how urine creatinine is used for collection checks, uACR and UPCR ratios, creatinine clearance, and why spot or 24-hour results can be high or low.

A urine creatinine test measures creatinine, a waste product generated from normal muscle metabolism, in a urine sample. It can be reported as a...

Urine Electrolyte Panel: Sodium, Potassium, Chloride, Osmolality, and Kidney Handling

Understand urine sodium, potassium, chloride, and osmolality patterns, kidney electrolyte handling, FENa, volume status, hyponatremia, and common interpretation pitfalls.

A urine electrolyte panel measures selected substances in urine—most often sodium, potassium, and chloride, with urine osmolality frequently added—to show how the kidneys are...

Urine Magnesium Test: High, Low, Kidney Loss, Mineral Balance, and Meaning

Learn how urine magnesium testing identifies kidney magnesium loss, how 24-hour magnesium and FEMg are interpreted, and what high or low results can mean.

A urine magnesium test measures how much magnesium the kidneys are excreting. It is most useful when blood magnesium is low and the clinician...

Urine Osmolal Gap Test: Ammonium Excretion, Metabolic Acidosis, and Kidney Acid Handling

Learn how the urine osmolal gap estimates ammonium excretion, how it helps evaluate normal-anion-gap metabolic acidosis, and when the calculation can mislead.

The urine osmolal gap is a calculated estimate of unmeasured particles in urine. In clinical nephrology, its main use is to roughly estimate urinary...

Urine Osmolality Test: High, Low, Hydration, Kidney Concentration, and Meaning

Understand urine osmolality results, including high and low values, hydration, hyponatremia, polyuria, kidney concentration, and diabetes insipidus evaluation.

A urine osmolality test measures how concentrated or dilute urine is by counting the number of dissolved particles per kilogram of water. The kidneys...