Estimates the driving force for potassium secretion in the cortical collecting duct — used to work up hyper- and hypokalaemia.
Written for clinicians. If you're a parent or patient, don't act on these numbers — talk to your child's doctor.
| Field | Unit | Notes |
|---|---|---|
| Urine potassium | mEq/L | 0–200 |
| Plasma potassium | mEq/L | 1–12 |
| Urine osmolality | mOsm/kg | 50–1400 |
| Plasma osmolality | mOsm/kg | 200–400 |
Estimates the driving force for potassium secretion in the cortical collecting duct — used to work up hyper- and hypokalaemia.
Urine potassium (mEq/L), Plasma potassium (mEq/L), Urine osmolality (mOsm/kg), Plasma osmolality (mOsm/kg).
The TTKG model has been questioned (medullary urea recycling); many nephrologists now favour the urine K/creatinine ratio. Use as one data point only.
Paediatric estimated GFR using the bedside Schwartz (2009) equation.
Urine anion gap to assess renal NH4+ excretion in normal-anion-gap metabolic acidosis.
Fraction of filtered sodium excreted in urine — helps distinguish prerenal from intrinsic (ATN) acute kidney injury.
Fraction of filtered urea excreted in urine — distinguishes prerenal from intrinsic AKI and stays valid in patients on diuretics.
Estimates serum osmolality from sodium, glucose and urea — compare with a measured value to derive the osmolar gap.
Fraction of filtered magnesium excreted in urine — distinguishes renal magnesium wasting from extrarenal loss in hypomagnesaemia.
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