Renal Function
The osmolality of a solution containing 1.0 mole of urea is equal to that of a solution containing
0.5 mole of NaCl
Serum osmolality remains relatively constant, whereas the urine osmolality ranges from
1 to 3 times that of serum
The ultrafiltrate in the urinary space of the glomerulus has a specific gravity of
1.010 and the same osmolality as the blood plasma
A 45 yr old female African American had her serum creatinine determined using a creatinine method that is not calibrated to an IDMS reference method. Her serum creatinine was 1.5 mg/dL. What is her eGFR using the appropriate MDRD equation?
48 mL/min/1.73m^2
The daily volume of urine excreted normally ranged from
500-1800mL/day
What results in an erroneous creatinine clearance measurement?
A 24 hr urine collection maintained at room temp throughout collection
The following data are obtained from a 60 yr old female who is 4'8" tall and weighs 88lb: Plasma creatinine: 1.2 mg/dL Urine creatinine: 500 mg/L Urine volume: 1440 mL/ 24 hr A- calculate the creatinine clearance. B- calculate the normalized creatinine clearance. C- are these results normal for this patient?
A-42 B-58 C-yes
A fluid deprivation test is used to
Assess renal concentrating ability
Renal clearance test equation
C (mL/min)= U(urine concentration)(mg/dL)• V(volume of urine)(mL/min)/ P(plasma concentration of substance)(mg/dL)
Creatinine clearance test equation
C(mL/min)= (U(urine creatinine) • V(urine volume)/ P(serum creatinine)) • 1.73m^2/ SA (height•weight)
Which renal function is assessed using specific gravity and osmolality measurements?
Concentrating ability
Which of the following is an endogenous substance used to measure glomerular filtration rate?
Creatinine
The concentration of which substances provides the best means of distinguishing urine from other body fluids?
Creatinine & urea
When the body is dehydrated the kidneys
Excrete solutes in as small a volume of urine as possible
The volume of plasma cleared per minute in excess of that required for solute elimination is called the
Free water clearance
A 24 hr urine collection is preferred for determination of creatinine clearance because of diurnal variation in the
Glomerular filtration rate
Which of the following solutes, if added to pure water, affects the specific gravity of the restraint solution more than it affects its osmolality?
Glucose
Creatinine is a good substance to use for a renal clearance test because
It has a constant plasma concentration
Occasionally the specific gravity of a urine specimen exceeds that physiologically possible (I.e >1.040). Which of the following substances when found in urine could account for such a high value?
Mannitol
Which of the following groups would be expected to have a the greatest 24 hr excretion of creatinine?
Men
Creatinine clearance results are "normalized" using an individuals body surface area to account for variations in the individuals
Muscle mass
Renal excretion is not involved in the elimination of
Normal byproducts of fat metabolism
Osmolality is a measure of solute
Number
Osmolatity
Number of solute particles per kilogram of solvent
The excretion of less than 400 mL of urine per day is called
Oliguria
A fluid deprivation test involves measurement of serum and urine
Osmolality
The maximum osmolality that urine can achieve is determined by the
Osmolality of the medullary interstitium
Renal clearance is defined as the volume of
Plasma cleared of a substance per minhte
Another name for excessive thirst is
Polydipsia
The excretion of large volumes of urine (>3 L/day) is called
Polyuria
What conditions can produce nocturia?
Pregnancy, chronic renal disease, fluid intake at night
Specific gravity measurements are not affected by
Solute charge
The glomerular filtration rate is controlled by
The renal blood flow
Which of the following are present in the largest molar amounts in urine?
Urea, chloride, sodium
