CNN Exam- Chronic Kidney Disease
Questions And Answers Updated 2026
List the limitations of the modification diet of renal disease (MDRD) and Cockgraft-Gault equations -
AnswerThe major limitation for both equations is that at glomerular filtration rates above 60, their
estimation is not accurate. The equation is much more accurate for stages II to V.
Cockgraft-Gault does not take into account ethnicity or nutritional status. The MDRD is preferred
because it has been extensively studied and takes into account other variables.
MDRD is limited in that it only accounts for 1 race (black). Other minority groups are not accounted
for and thus their GFR may not be truly representative.
***TAKE AWAY*** Both are less accurate with GFR greater than 60.
List the Cockgraft-Gault equation - AnswerCalculated by the following:
(140-age) x lean body mass (kg) / serum creatinine (mg/dl) x 72. The equation is further modified by
multiplying the result by 0.85 for woman (as a way for accounting for the lower body mass).
The Cockgraft-Gault equation is easily memorized and only requires one blood test to calculate, the
serum creatinine.
Limited by variances in the body mass (relies on serum creatinine for calculations). Can be over or
under estimated based on GFR.
It also loses accuracy in patients with amputated limbs, particularly the lower extremity
List the Modification Diet of Renal Disease equation - AnswerCalculated by using:
(Age) exp[-0.176] x (BUN [mg/dl]) exp[-0.170] x (Alb [g/dl]) exp[+0.318] x (0.762 if female0 x (1.18 if
black)
Complicated equation and shouldn't be memorized.
-Regarded as being more accurate method
-Widely studied and also accounts for nutrition and ethnicity
, -Limitations include losing accuracy at GFR greater than 60 and lab errors
-Serum BUN and albumin required and if inaccurate or inconsistent, will be effected
-Limited by patients with unusual body mass as is seen with obese, malnourished and amputees
Describe appropriate dialysate calcium concentrations in patients on either hemodialysis or
peritoneal dialysis - AnswerThe dialysate concentration is normally set to 2.5 mEq/L. At this
concentration, little or no calcium is exchanged between dialysate and the serum.
In patients with elevated calcium levels a lower dialysate concentration will be needed to remove
excess calcium. Conversely, if patients need calcium, a dialysate concentration of 3.5 mEq/L will
provide calcium to the patient. Initial therapy to raise the serum calcium level is through both
calcium and vitamin D supplementation.
Describe the kidney's role in calcium and phosphorus homeostasis - AnswerThe kidney is
instrumental in excreting excess phosphorous and producing the active form of vitamin D, called
calcitriol.
Calcitriol is a hormone which travels to the gut and aids in both phosphorus and calcium absorption.
Moreover, calcium phosphorus is regulated by the hormones PTH (parathyroid hormone). PTH is
released from the parathyroid gland and functions to elevate serum calcium levels and lower
phosphorus levels.
***Note that the kidneys are involved in both phosphorus excretion (under influence of PTH) and
phosphorus absorption via calcitriol.
Discuss the pathophysiology of aluminum toxicity in patients with chronic kidney disease -
AnswerAluminum is excreted by the kidneys. In patients with renal disease, the ability to excrete
aluminum is hindered. Aluminum toxicity was a much larger problem when aluminum based
phosphate binders were used. The aluminum would be absorbed by the gut and accumulate over
time.
Aluminum causes the following abnormalities:
- acute toxicity
- dementia
- osteomalacia
- anemia
Questions And Answers Updated 2026
List the limitations of the modification diet of renal disease (MDRD) and Cockgraft-Gault equations -
AnswerThe major limitation for both equations is that at glomerular filtration rates above 60, their
estimation is not accurate. The equation is much more accurate for stages II to V.
Cockgraft-Gault does not take into account ethnicity or nutritional status. The MDRD is preferred
because it has been extensively studied and takes into account other variables.
MDRD is limited in that it only accounts for 1 race (black). Other minority groups are not accounted
for and thus their GFR may not be truly representative.
***TAKE AWAY*** Both are less accurate with GFR greater than 60.
List the Cockgraft-Gault equation - AnswerCalculated by the following:
(140-age) x lean body mass (kg) / serum creatinine (mg/dl) x 72. The equation is further modified by
multiplying the result by 0.85 for woman (as a way for accounting for the lower body mass).
The Cockgraft-Gault equation is easily memorized and only requires one blood test to calculate, the
serum creatinine.
Limited by variances in the body mass (relies on serum creatinine for calculations). Can be over or
under estimated based on GFR.
It also loses accuracy in patients with amputated limbs, particularly the lower extremity
List the Modification Diet of Renal Disease equation - AnswerCalculated by using:
(Age) exp[-0.176] x (BUN [mg/dl]) exp[-0.170] x (Alb [g/dl]) exp[+0.318] x (0.762 if female0 x (1.18 if
black)
Complicated equation and shouldn't be memorized.
-Regarded as being more accurate method
-Widely studied and also accounts for nutrition and ethnicity
, -Limitations include losing accuracy at GFR greater than 60 and lab errors
-Serum BUN and albumin required and if inaccurate or inconsistent, will be effected
-Limited by patients with unusual body mass as is seen with obese, malnourished and amputees
Describe appropriate dialysate calcium concentrations in patients on either hemodialysis or
peritoneal dialysis - AnswerThe dialysate concentration is normally set to 2.5 mEq/L. At this
concentration, little or no calcium is exchanged between dialysate and the serum.
In patients with elevated calcium levels a lower dialysate concentration will be needed to remove
excess calcium. Conversely, if patients need calcium, a dialysate concentration of 3.5 mEq/L will
provide calcium to the patient. Initial therapy to raise the serum calcium level is through both
calcium and vitamin D supplementation.
Describe the kidney's role in calcium and phosphorus homeostasis - AnswerThe kidney is
instrumental in excreting excess phosphorous and producing the active form of vitamin D, called
calcitriol.
Calcitriol is a hormone which travels to the gut and aids in both phosphorus and calcium absorption.
Moreover, calcium phosphorus is regulated by the hormones PTH (parathyroid hormone). PTH is
released from the parathyroid gland and functions to elevate serum calcium levels and lower
phosphorus levels.
***Note that the kidneys are involved in both phosphorus excretion (under influence of PTH) and
phosphorus absorption via calcitriol.
Discuss the pathophysiology of aluminum toxicity in patients with chronic kidney disease -
AnswerAluminum is excreted by the kidneys. In patients with renal disease, the ability to excrete
aluminum is hindered. Aluminum toxicity was a much larger problem when aluminum based
phosphate binders were used. The aluminum would be absorbed by the gut and accumulate over
time.
Aluminum causes the following abnormalities:
- acute toxicity
- dementia
- osteomalacia
- anemia
