Renal Function Tests — Flashcards

Flashcard 1: The _____ ratio is used as a marker for water reabsorption along the nephron

Answer: [TF/P]inulin

Flashcard 2: _____ clearance can be used to calculate effective renal plasma flow (eRPF) because it is both filtered and secreted

Answer: Para-aminohippuric acid (PAH)

Flashcard 3: Renal blood flow (RBF) remains relatively constant between mean arterial pressure (MAP) ranges of _____ to 180 mmHg

Answer: 80

Flashcard 4: PCT cells are involved in sustaining _____ which increases solute and water reabsorption in response to increased GFR.

Answer: glomerulotubular balance

Flashcard 5: When CH2O is _____, urine is hypo-osmotic relative to plasma

Answer: positive

Flashcard 6: The amount of _____ excreted in the urine is directly proportional to muscle mass

Answer: creatinine

Flashcard 7: _____ is cleared only via glomeruli with no tubular excretion and hence used for direct measurement of GFR.

Answer: Tc-99m DTPA (diethylene-triamine-pentaacetate)

Flashcard 8: A good rule of thumb for the relationship between GFR and serum creatinine is that everytime GFR _____, serum creatinine doubles

Answer: halves

Flashcard 9: What is the formula for renal clearance ($C_x$)?

Answer: $C_x = \frac{U_x V}{P_x}$

Extra: $U_x$ = Urine concentration of X $P_x$ = Plasma concentration of X $V$ = Urine flow rate

Flashcard 10: What equation is used to calculate **free-water clearance** ($C_{H_2O}$)?

Answer: $$C_{H_2O} = V - C_{osm}$$ (where $V$ = urine flow rate; $C_{osm}$ = osmolar clearance)

Extra: Free-water clearance ($C_{H_2O}$) represents the volume of solute-free water that must be added to or removed from the urine to make it isotonic with plasma. - If **$C_{H_2O} = 0$**: Urine is isosthenuric (isosmotic to plasma). - If **$C_{H_2O} > 0$**: Free water is excreted (dilute urine; $U_{osm} < P_{osm}$). Seen in low ADH states (e.g., diabetes insipidus, water intoxication). - If **$C_{H_2O} < 0$**: Free water is reabsorbed (concentrated urine; $U_{osm} > P_{osm}$). Seen in high ADH states (e.g., SIADH, dehydration).