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Kaplan Qbank USMLE



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i find myself always confused with this term TTKG. found this explanation simple enough:


Definition

• A calculated measurement which estimates the tubular fluid potassium concentration at the end of the

cortical collecting tubule, the site responsible for most of potassium secretion

• In simplest terms, think of the TTKG as a rough measurement of aldosterone activity in the kidney

TTKG = 8-9 in normal subject on a normal diet



Practical Application

• HYPERKALEMIA (TYPICALLY PERSISTENT HIGH K+)



♦ Use the TTKG to determine if high K+ is from low aldosterone states or from decreased effective circulating volume (in CHF, etc.)

♦ In low aldosterone states, K+ in the cortical collecting tubule should be low and thus the TTKG should be low

O If hypoaldosterone state, TTKG < 5

O If decreased ECV, TTKG > 7



• HYPOKALEMIA (PERSISTENT)



♦ Use the TTKG to determine renal vs. non-renal loss of potassium

♦ If loss is renal, assume hyperaldosterone state and thus K+ at the cortical collecting duct should be high and thus the TTKG should be high

O If renal loss of K+, TTKG > 7

O If non-renal loss, TTKG < 5 (should be hypoaldo from low K+)


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