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TTKG
(a.k.a TransTubular Potassium Gradient)
24 Hour Urine (no Preservative)(Phone (82)4712 to order)
Tube type: Plain 24hr Urine
Special instructions
Must send paired serum (SST gold top) with a Plain 24 hour Urine collection (no preservative). Random urine also accepted although 24 hour collection most accurate.
For TTKG calculation you will currently need to request osmolality and potassium for both urine and serum samples. Please contact duty biochemsit (x4050) to provide TTKG calculation and ensure tests are complete.
Contact Laboratory before requesting
Units
NA
Turnaround Time
7
days
Department: Biochemistry
Clinical Application
TTKG may be useful in diagnosing causes of unexplained hypokalaemia and hyperkalaemia. Use the TTKG to evaluate the adequacy of renal response using 24 hour urine collection for potassium excretion. Other useful tests include serum bicarbonate to assess patient acid-base status and urine chloride and urine calcium
TTKG = (Urine potassium x Serum Osm)/(Serum potassium x Urine Osm)
Normal TTKG varies and reflects conservation of potassium in collecting ducts of kidneys. In adults:
During hypokalaemia (K+ <3.5 mmol/L), TTKG should be <3. A value >3 suggests renal potassium wasting.
During hyperkalaemia (K+>5.0 mmol/L). TTKG >10 suggests normal renal excretion of potassium as long as normal kidney and adrenal function is present.
Urine sodium should be at least 25mmol/L for calculation to be accurate.
Hypokalaemia
Severe hypokalaemia <2.5 mmol/L or symptomatic should be evaluated urgently.
Please see link below to RUH Biochemistry Clinical Guideline: Hypokalaemia
Consider patient history, medications and check blood pressure and serum magnesium. Further second line investigations can be complex so it is advised to telephone duty biochemist for discussion if persistent hypokalaemia that cannot be explained.
During hypokalaemia (K+ <3.5 mmol/L), TTKG should be <3. A Greater value suggests renal potassium wasting.
Hyperkalaemia
Urgent referral to secondary care recommended for patients if K ≥6.5 mmol/L, K ≥5.5 mmol/L with acute ECG changes or acute changes >0.5mmol within 6-12 hours.
Please see link below to RUH Biochemistry Clinical Guideline: Hyperkalaemia
During hyperkalaemia (K+>5.0 mmol/L). TTKG >10 suggests normal renal excretion of potassium.
Further second line investigations can be complex so it is advised to telephone duty biochemist if persistent hyperkalaemia that cannot be explained.
Updated 16 Dec 2025 by C.Padget
Links:
» Patient instructions for 24h Urine Potassium Collection
» RUH Hyperkalaemia guidance
» RUH Hypokalaemia guidance
