Chronic kidney disease: "defined as kidney damage or GFR < 60 ml/min/1.73m^{2 }for
3 months.
Kidney damage is defined as pathologic abnormalities or markers of damage,
including abnormalities in blood or urine tests or imaging studies." ^{9}

Restrict the maximum calculated clearance to this value:

Cockcroft and Gault equation utilizing the tbw (Total body
weight) to calculate an estimated creatinine clearance

Cockcroft and Gault equation:
CrCl = [(140 - age) x TBW] / (Scr x 72) (x 0.85 for females)

Cockcroft and Gault equation utilizing the ibw (Ideal body weight) to
calculate an estimated creatinine clearance

Cockcroft and Gault equation:
CrCl = [(140 - age) x IBW] / (Scr x 72) (x 0.85 for females)
Note: if the ABW (actual body weight) is less than the IBW use the
actual body weight for calculating the CRCL.

Estimate Ideal body weight in (kg)
Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.
Females: IBW = 45.5 kg + 2.3 kg for each inch over 5 feet.

Cockcroft and Gault equation utilizing the adjusted body weight to calculate
an estimated creatinine clearance.

CrCl = [(140 - age) x AjBW] / (Scr x 72)

Note: (Multiply result by 0.85 for females)
AjBW = adjusted body weight:
AjBW = IBW + 0.4( ABW - IBW)

Estimated IBW:
Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.
Females: IBW = 45.5 kg + 2.3 kg for each inch over 5 feet.

Some studies have shown that utilizing the adjusted body weight improves
accuracy compared to other commonly used equations in estimating the
creatinine clearance in the elderly population.

Simplified 4-variable MDRD study formula

GFR = 186.3 x (SCR)^{-1.154} x (age in
years)^{-0.203} x 1.212 (if patient is black) x 0.742 (if female)

Key point: Early statistical analysis shows very promising results. May
represent the most accurate choice of this group. This may be especially
true in chronic kidney disease.

CKD-EPI equation

GFR = 141 x min(Scr/κ,1)^{α} x max(Scr/κ,1)^{-1.209}
x 0.993^{Age} x 1.018 [if
female]
x 1.159 [if black]

κ = 0.7 if female.
κ = 0.9 if male.

α = -0.329 if female
α = -0.411 if male

min = the minimum of Scr/κ or 1
max = the maximum of Scr/κ or 1

"BACKGROUND: Equations to estimate glomerular filtration
rate (GFR) are routinely used to assess kidney function. Current
equations have limited precision and systematically underestimate
measured GFR at higher values."^{ 1}

"CONCLUSION: The CKD-EPI creatinine equation is more accurate than
the Modification of Diet in Renal Disease Study equation and could
replace it for routine clinical use."^{ 13}

References

Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum
creatinine. Nephron 1976;16(1):31-41

Davis GA, Chandler MH. Comparison of creatinine clearance estimation
methods in patients with trauma. Am J Health-Syst Pharm 1996;53:1028-32.

Demirovic JA, Pai AB, Pai MP. Estimation of
creatinine clearance in morbidly obese patients. Am J Health Syst Pharm.
2009 Apr 1;66(7):642-8.

"An LBW estimate, based on TBW and BMI,
incorporated into the Cockcroft-Gault equation provided an unbiased,
relatively precise, accurate, and clinically practical estimate of
24-hour measured CLcr in morbidly obese patients."

Lean body weight - male:
9270 x tbw/6680 + 216 x BMI
Lean body weight - female:
9270 x tbw/8780 + 244 x BMI

Obese study population: As expected, use of Cockcroft-Gault_{TBW}
grossly overestimated measured CL_{cr}. The Cockcroft-GaultABW_{0.3},
Cockcroft-GaultABW_{0.4}, and Salazar-Corcoran
equations all overestimated measured CL_{cr} values in the study patients. In
contrast, the Cockcroft-Gault_{IBW} and the MDRD4 equations
underestimated measured CL_{cr} values. The Cockcroft-Gault_{LBW}
equation was the most precise, and the MDRD4 equation was the least. The
Cockcroft-Gault_{FFW} and Cockcroft- Gault_{LBW}
equations yielded the highest accuracy (55-61%), in yielding values that
were within 30% of the measured CL_{cr}.

Dettli LC. Drug dosage in patients with renal disease. Clin Pharmacol
Ther 1974;16:274-80.

Drusano LG, Munice HL, Hoopes JM et al. Commonly used methods of
estimating creatinine clearance are inadequate for elderly debilitated
nursing home patients. J Am Geriatrics Soc 1998;36:437-41.

Hailemeskel B, Namanny M, Kurz A. Estimating aminoglycoside dosage
requirements in patients with low serum creatinine concentrations. Am J
Health-Syst Pharm 1997;54:986-7.

Jelliffe RW. Estimation of creatinine clearance when urine cannot be
collected. Lancet 1971;1:975-6.

Levey AS, Greene T, Kusek JW, et al. A simplified equation to predict
glomerular filtration rate from serum creatinine (Abstr) J Am Soc Nephrol
2000;(11):155A

Levey AS, Greene T, Schluchter MD, et al. Glomerular filtration rate
measurements in clinical trials. Modification of Diet in Renal Disease Study
Group and the Diabetes Control and Complications Trial Research Group. J Am
Soc Nephrol 1993;4(5):1159-71

Levey AS. Assessing the effectiveness of therapy to prevent the
progression of renal disease. Am J Kidney Dis 1993;22(1):207-14

Levey AS, Bosch JP, Lewis JB, et al. A more accurate method to estimate
glomerular filtration rate from serum creatinine: a new prediction equation.
Modification of Diet in Renal Disease Study Group. Ann Intern Med
1999;130(6):461-70

Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF 3rd, Feldman HI,
Kusek JW, Eggers P, Van Lente F, Greene T, Coresh J. A New
Equation to Estimate Glomerular Filtration Rate.
Ann Intern Med. 2009; 150:604-612.

Rhodes RS, Sims PJ, Culbertson VL et al. Accuracy of creatinine
clearance estimates in geriatric males with elevated serum creatinine
clearance. J Geriatric Drug Ther 1991;5:31-45.

Salazar DE, Corcoran GB: Predicting creatinine clearance and renal
drug clearance in obese patients from estimated fat-free body mass. Am J
Med 84: 1053-1060, 1988.

Smythe M, Hoffman J, Kizy K et al. Estimating creatinine clearance in
elderly patients with low serum creatinine concentrations. Am J Hosp Pharm
1994;51:189-204.

Wilhelm SM, Pramodini KP. Estimating
Creatinine Clearance: A Meta-analysis. Pharmacotherapy 2011 31:7 ,
658-664.

"Conclusion. Using the Cockcroft-Gault equation with no
body weight (NBW) and actual Scr value most closely estimated measured
Clcr. In obese patients, it may be reasonable to use actual body weight
with a correction factor of 0.3 or 0.4 and actual Scr value in the
Cockcroft-Gault equation. Based on this analysis, the use of total body
weight, ideal body weight, and a rounded Scr value cannot be
recommended."

Winter MA, Guhr KN, Berg GM. Impact of various body weights and
serum creatinine concentrations on the bias and accuracy of the
Cockcroft-Gault equation. Pharmacotherapy 2012; 32: 604-612 [PMID:
22576791 DOI: 10.1002/j.1875-9114.2012.01098.x]

Quotes: [Largest study so far....total of
3678 patients] Regarding Salazar equation: This equation,
however, was not consistently shown in studies to be a
superior predictor of renal function. It is not widely used in
clinical practice and has not been validated in
pharmacokinetic studies. In addition, the Salazar-Corcoran
equation is not recognized by the National Kidney Foundation.

Regarding CG -LBW equation: Our findings do
not support those conclusions and are different from a recent
investigation of Clcr in 54 morbidly obese patients that found
that adjusting an obese patient’s weight to a fat-free weight
or lean body weight predicted a Clcr calculated with the C-G
equation without bias. Notably,
our study included 2065 obese or morbidly obese patients, far
more than other published studies.

Conclusions: An unbiased C-G Clcr can be
calculated using actual body weight in underweight patients
and ideal body weight in patients of normal weight. Using
ABW0.4 for overweight, obese, and morbidly obese patients
appears to be the least biased and most accurate method for
calculating their C-G Clcr. Rounding Scr in patients with low
Scr did not improve accuracy or bias of the Clcr calculations.

If the actual body
weight is less than any of the calculation methods, the actual body
weight will be used. Discussion of the various methods: The
output of this section is based on research I had completed ~20 years
ago on this subject. A quick review of the recent literature has
not changed or added any new methods for estimating an ideal body weight
for patients less than 60 inches tall. Note: naming convention is
based on my earlier work...

1] IntuitiveMethod: Reference: Murdaugh LB. Competence Assessment Tools for
Health-System Pharmacies. 5th ed. Bethesda, MD: ASHP; 2015. [Chap:29 Medication
dosing in Patients with Renal Dysfunction]
IBW (Male) = 50kg - 2.3kg for each inch below 60 inches
IBW (Female) = 45.5kg - 2.3kg for each inch below 60 inches Comments: For patients just a few inches below 60
inches, the result is reasonable, however, 2.3 kg/inch is excessive when
used for shorter heights. At 38 inches for a male, and 40 inches
for a female, the IBW is ZERO. This provides support for the
next method below.

2] Baseline Method:
The baseline method starts with the initial ideal body weight baseline
values e.g. 60 inch male patient - 50kg and 60 inch female patient -
45.5kg. Male patient: 50kg /60 inches = 0.833 kg/inch.
Female patient = 45.5kg/60 inches = 0.758 kg/inch. Therefore
a male patient - 55 inches: IBW = 50kg - (0.833 x 5) = 45.8kg versus the
first method = 50kg - (2.3 x 5) = 38.5 kg.
[Reference: reasonable assumption based on the standard ideal body weight
equations and the baseline weights established for a height of 60 inches. Also review: Murphy JE. Introduction. In: Murphy JE, ed. Clinical Pharmacokinetics, 5th ed. Bethesda, MD: American Society of Health-System Pharmacists, 2011:xxxiv.
- Note: for patients who are less than 60 inches tall, the weight should be decreased more conservatively than 2.3kg/inch.]

3] BMI method:

References:
Wiggins, K. L. (2004). Renal care: Resources and practical applications.
Chicago: American Dietetic Association. pg 12.

Barash, P. G., Cullen, B. F., & Stoelting, R. K. (1989). Clinical anesthesia.
Philadelphia: Lippincott. chap:47:1231

Remember that BMI = weight(kg)/height^{2} (meters squared).
Next, we will establish an 'ideal' BMI based on values in the standard
IBW equations: Male: 60 inches - 50kg - BMI= 21.53. Female:
60 inches - 45.5kg - BMI= 19.59. We can then use this association
to generate an equivalent ideal weight based on this standardized BMI
and the height of the patient. Using the example above (55 inch
male patient):
IBW = 21.53 (BMI value above) x (55 x 0.0254)^{2} =
42 kg.
Background info: the body mass index quantifies the amount of tissue mass at a
particular height (units: kg/m^{2}). Example: the following
patients all have a BMI ~ 21: 130 lbs - 5'6", 163 lbs - 6'2",
107 lbs - 5'.

BMI

19

20

21

Height
(inches)

Body
Weight (pounds)

58

91

96

100

59

94

99

104

60

97

102

107

61

100

106

111

62

104

109

115

63

107

113

118

64

110

116

122

65

114

120

126

66

118

124

130

67

121

127

134

68

125

131

138

69

128

135

142

70

132

139

146

71

136

143

150

72

140

147

154

73

144

151

159

74

148

155

163

4] Hume method:
LBW (Males) = (0.3281 x Weight in kg) + (0.33939 x Height in cm) -
29.5336
LBW (Females) = (0.29569 x Weight in kg) + (0.41813 x Height in cm) -
43.2933
Using the example above: (55 inch male patient): IBW=
36.9 kg

Reference: Hume R. Prediction of lean body mass from height and
weight. J Clin Path(1966), 19, 389.

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