CNN Exam – chronic kidney disease 2026 – Study Guide and
Practice Questions
List the limitations of the modification diet of renal disease (MDRD) and Cockroft-Gault
equations - correct answer ✔✔ The 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 - correct answer ✔✔ Calculated 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 - correct answer ✔✔ Calculated 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 - correct answer ✔✔ The 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 - correct answer ✔✔ The
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.
Practice Questions
List the limitations of the modification diet of renal disease (MDRD) and Cockroft-Gault
equations - correct answer ✔✔ The 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 - correct answer ✔✔ Calculated 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 - correct answer ✔✔ Calculated 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 - correct answer ✔✔ The 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 - correct answer ✔✔ The
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.
