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🧪

Transtubular Potassium Gradient (TTKG)

TTKG estimates potassium concentration in the cortical collecting duct, helping differentiate renal vs extrarenal causes of potassium disorders.

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HyperK: TTKG >10 = appropriate; <6 = renal cause HypoK: TTKG <3 = appropriate; >4 = renal wasting Urine Osm >300 mOsm/kg ideal for accuracy

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Why: TTKG differentiates hypoaldosteronism from extrarenal causes in hyperkalemia, and renal wasting from GI losses in hypokalemia.

How: TTKG = (Urine K / Serum K) ÷ (Urine Osm / Serum Osm). Urine osmolality must exceed serum for valid result.

HyperK: TTKG >10 = appropriate; <6 = renal causeHypoK: TTKG <3 = appropriate; >4 = renal wasting
Sources:KDIGO GuidelinesUpToDate - TTKG

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🧪 Sample Clinical Scenarios — Click to Load

Laboratory Values

Serum potassium concentration
mEq/L
Spot urine potassium
mEq/L
Serum osmolality
mOsm/kg
Must be >300 for valid TTKG
mOsm/kg

Clinical Context

Indication for TTKG
Known aldosterone if available
Affects TTKG interpretation
Patient age
years

For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.

🏥 Health Facts

🧪

TTKG reflects aldosterone-mediated K+ secretion in cortical collecting duct

— Nephrology

⚖️

Osmolality correction accounts for water reabsorption concentrating urine K+

— Physiology

📋 Key Takeaways

  • • TTKG estimates potassium concentration in the cortical collecting duct
  • • Hyperkalemia: TTKG >10 = appropriate renal response; <6 = renal cause
  • • Hypokalemia: TTKG <3 = appropriate conservation; >4 = renal wasting
  • • Urine osmolality must exceed serum osmolality for valid TTKG
  • • Diuretics significantly affect TTKG interpretation

💡 Did You Know?

🧪TTKG reflects aldosterone-mediated K+ secretion in cortical collecting ductSource: Nephrology
⚖️Osmolality correction accounts for water reabsorption concentrating urine K+Source: Physiology
📉Low TTKG in hyperkalemia suggests hypoaldosteronism or type 4 RTASource: Clinical guidelines
📈High TTKG in hypokalemia indicates renal wasting: hyperaldosteronism or diureticsSource: Clinical guidelines
💊Loop/thiazide raise TTKG; K-sparing diuretics lower itSource: Pharmacology
🔬Urine Osm &gt;300 mOsm/kg ideal for accurate TTKGSource: Laboratory medicine

📖 How It Works

TTKG estimates the potassium gradient in the cortical collecting duct, correcting for medullary water reabsorption.

Step 1: Collect Simultaneous Samples

Serum and spot urine for K+ and osmolality. Urine Osm must exceed serum Osm.

Step 2: Calculate Osmolality Ratio

Corrects for water reabsorption in medullary collecting duct.

Step 3: Apply TTKG Formula

TTKG = (UK/SerumK) ÷ (UrineOsm/SerumOsm)

🎯 Expert Tips

Validity Check

Always verify urine Osm > serum Osm before interpreting TTKG.

Sample Timing

Obtain serum and urine samples at the same time.

Medication Effects

Consider ACEi, ARBs, K-sparing diuretics when interpreting.

Follow-up

Aldosterone/renin testing if mineralocorticoid disorder suspected.

⚖️ TTKG vs Alternatives

ToolRenal vs ExtrarenalSpot Urine
TTKG✅✅
24h urine K+✅❌
FENaPrerenal vs ATN✅

❓ FAQ

When is TTKG not valid?

When urine osmolality &lt; serum osmolality (dilute urine). Ideally urine Osm &gt;300 mOsm/kg.

What causes low TTKG in hyperkalemia?

Hypoaldosteronism, type 4 RTA, ACEi/ARBs, K-sparing diuretics, distal nephron dysfunction.

What causes high TTKG in hypokalemia?

Hyperaldosteronism, diuretics, Bartter/Gitelman, RTA types 1 and 2, hypomagnesemia.

How do diuretics affect TTKG?

Loop and thiazide increase TTKG; potassium-sparing decrease it.

Can TTKG diagnose hyperaldosteronism?

TTKG suggests it but is not diagnostic. Elevated TTKG in hypokalemia with HTN warrants aldosterone-to-renin ratio.

📊 Reference Ranges

>10
HyperK appropriate
<6
HyperK renal cause
<3
HypoK appropriate
>4
HypoK renal wasting

⚠️ Disclaimer: This calculator is for educational purposes only. TTKG has limitations. Always consult a qualified healthcare provider.

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