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**II. Indications**

- Creatinine Clearance estimates Glomerular Filtration Rate (GFR)

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**III. Interpretation: Normal Creatinine Clearance**

- Men
- Average: 120 ml/min/1.73 m2 (+/-25) or 175 Liters/day
- Range: 97-137 ml/min/1.73 m2 (0.93-1.32 ml/sec/m2 IU)

- Women
- Average: 95 ml/min/1.73 m2 (+/-20) or 135 Liters/day
- Range: 88-128 ml/min/1.73 m2 (0.85-1.23 ml/sec/m2 IU)

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**IV. Calculation: Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)**

- Calculation
- Males: 141 * min (sCr/0.9 or 1) ^ -0.411 * max(sCr/0.9 or 1)^ - 1.209 * 0.993 ^ ageY
- Females: 141 * min (sCr/0.7 or 1) ^ -0.329 * max(sCr/0.7 or 1)^ - 1.209 * 0.993 ^ ageY * 1.018
- Black: Multiply above equation (based on gender) by 1.159
- Applying black race variable is NOT recommended

- Annotation
- Where sCr is Serum Creatinine
- Min is the minimum value (either that calculated or 1)
- Max is the maximum value (either that calculated or 1)
- Where ^ represents to the power of...

- Efficacy
- More accurate than either CKD or MDRD
- Preferred method of eGFR calculation (without race variable)

- Alternatives
- GFR may also be estimated from Serum Cystatin C instead of Serum Creatinine
- Consider if abnormal GFR based on Creatinine Clearance suspected to be False Positive

- GFR may also be estimated from Serum Cystatin C instead of Serum Creatinine
- Resources
- National Kidney Foundation

- References

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**V. Calculation: Cockcroft-Gault formula for GFR estimate**

- Indications: Stable Kidney Function
- As of 2017, primarily used only for medication Renal Dosing (other calculations are preferred)
- Older patients
- General screening

- Male GFR = (140 - age) x (weight) / (sCr x 72)
- Female GFR = (140 - age) x (weight) x 0.85 / (sCr x 72)
- Annotation
- Where GFR is Glomerular Filtration Rate in ml/min
- Where age is in years
- Where weight is Lean Body Mass in kilograms
- Where sCr is Serum Creatinine in mg/dl

- Efficacy
- As accurate as 24 hour urine in most cases
- Exceptions: See 24 hour CrCl indications below

- Resources: GFR Calculator

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**VI. Calculation: Abbreviated MDRD Study Equation**

- Indications: Chronic Kidney Disease, stable function
- Middle aged patients
- Black patients
- Diabetic Nephropathy
- Status-post Kidney Transplant

- Efficacy
- More accurate than Cockroft-Gault in CRF
- Overestimates Chronic Kidney Disease when used as a general screening tool
- Underestimates GFR in the absence of Kidney disease
- Rule (2004) Ann Intern Med 141:929-37 [PubMed]

- Formula: GFR = 186 x (sCr)^-1.154 x (age)^-0.203
- Where sCr is raised by power of -1.154
- Where age is raised by power of -0.203

- Modifiers
- Female: Multiply GFR by 0.742
- Black: Multiply GFR by 1.210

- Annotation
- Where GFR=Glomerular Filtration Rate ml/min/1.73 m2
- Where sCr is Serum Creatinine in mg/dl

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**VII. Calculation: 24 hour Creatinine Clearance**

- Previously considered gold standard GFR evaluation
- Now thought to be less accurate than calculations (see above) due to flawed collection

- Indications
- Pregnancy
- Severely underweight or Overweight
- Very young and very old
- Malnutrition
- Skeletal Muscle disorders, Paraplegia, Quadriplegia

- Formula
- CrCl = (uCr x uV) / (sCr x 1440)

- Annotation
- Where CrCl is Creatinine Clearance in ml/min
- Where uCr is Urine Creatinine in mg/dl
- Where sCr is Serum Creatinine in mg/dl
- Where uV is 24 hour Urine Volume in ml
- Where 1440 represents number of minutes in 24 hours

- Indications (where calculation above is inaccurate)
- Altered Protein intake
- Vegetarian Diet
- Creatine Supplementation

- Altered Muscle mass
- Malnutrition or Muscle wasting
- Amputation

- Altered Protein intake

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**VIII. Interpretation: Increased GFR**

- Pregnancy
- Exercise

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**IX. Interpretation: Decreased GFR**

- Chronic Kidney Disease or Renal Insufficiency
- Advanced age
- Normal GFR is 125 ml/min/1.73 m2 at age 30 years
- GFR decreases by 1 ml/min/year over age 30 years

- Inadequate urine specimen collection
- See Urine Creatinine for judging adequacy

- Medications (Decrease tubular secretion of Creatinine)
- Cimetidine
- Procainamide
- Antibiotics
- Quinidine

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**X. Precautions: Pitfalls**

- Creatinine Clearance (CrCl) and estimated Glomerular Filtration Rate (eGFR) are NOT interchangeable
- Older dosing guidelines and precautions were given in CrCl, but newer guidelines refer to eGFR
- CrCl units are ml/min
- eGFR units are ml/min/1.73m^2

- Drug dosing guidelines are specific for their cutoff ranges
- Using eGFR when CrCl is indicated will miss dose adjustments in up to 50% of cases
- Highest risk for miscalculation is in the elderly and in moderate to severe Chronic Kidney Disease

- Older dosing guidelines and precautions were given in CrCl, but newer guidelines refer to eGFR
- Calculating GFR in specific cohorts
- As of 2020, guidelines recommend calculating eGFR without regard to race
- Overweight (bodyweight >20-30% over Ideal Weight)
- Calculate based on adjusted body weight
- Adjusted body weight = wtKgIdeal + 0.4 * (wtKgActual - wtKgIdeal)

- Underweight
- Use actual weight
- Do not round up when calculating CrCl (significantly underestimates GFR)

- Alternative calculation for patients well above or below their Ideal Body Weight
- Corrected eGFR = eGFR * BSA/1.73 m2

- Elderly
- Do not round up when calculating CrCl (significantly underestimates GFR)

- Limb Amputation or Quadriplegic
- Measure 24 hour Creatinine Clearance

- Abnormal Creatinine Clearance suspected to be False Positive
- Serum Cystatin C may be used as alternative to Serum Creatinine

- Creatinine Clearance (by 24 hour urine) is overestimated at decreased GFR
- As GFR decreases, secreted Creatinine makes up larger percentage of total Urine Creatinine
- Consider pre-medicating the 24 hour Urine Collection
- Give Cimetidine or Trimethoprim for 2 days prior to 24 hour Urine Collection
- Overcomes the over-estimatation of GFR