calculate_ttkg: Transtubular Potassium Gradient (TTKG)

In cliot: Clinical Indices and Outcomes Tools

Transtubular Potassium Gradient (TTKG)

Description

Calculates the Transtubular Potassium Gradient (TTKG), a semi-quantitative index of the potassium secretory process in the cortical collecting duct. It is used to distinguish between renal and extra-renal causes of potassium imbalance (hypokalemia or hyperkalemia). The calculation requires urine osmolality to be greater than serum osmolality to be valid.

Usage

calculate_ttkg(urine_potassium, serum_potassium, urine_osmolality, serum_osmolality)

Arguments

urine_potassium	Numeric. Urine potassium concentration in mmol/L (or mEq/L).
serum_potassium	Numeric. Serum potassium concentration in mmol/L (or mEq/L).
urine_osmolality	Numeric. Urine osmolality in mOsm/kg.
serum_osmolality	Numeric. Serum osmolality in mOsm/kg.

Details

The formula is:

TTKG = \frac{Urine_{K} \times Serum_{Osm}}{Serum_{K} \times Urine_{Osm}}

**Validity condition:** The formula assumes that water is reabsorbed in the medullary collecting duct, which requires Urine_{Osm} > Serum_{Osm}. If this condition is not met, the result is physiologically invalid.

Value

A list containing:

TTKG_Score	The calculated gradient value.
Validity	Status indicating if the osmotic condition for calculation was met.
Interpretation	Clinical context based on standard thresholds (<3 or >7).

References

Ethier JH, Kamel KS, Magner PO, Lemann J Jr, Halperin ML. The transtubular potassium concentration in patients with hypokalemia and hyperkalemia. Am J Kidney Dis. 1990;15(4):309-315. doi:10.1016/s0272-6386(12)80076-x

Examples

# Example 1: Renal K+ Wasting (Hyperaldosteronism context)
# Urine K 40, Serum K 3.0, Urine Osm 600, Serum Osm 290
# TTKG = (40 * 290) / (3.0 * 600) = 11600 / 1800 = 6.44
calculate_ttkg(40, 3.0, 600, 290)

# Example 2: Invalid Calculation (Dilute Urine)
# Urine Osm < Serum Osm
calculate_ttkg(10, 4.0, 200, 290)

cliot documentation built on Dec. 1, 2025, 1:06 a.m.