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Creatinine Clearance (Cockcroft-Gault) Practice

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Creatinine clearance estimates kidney function to guide renal dose adjustments. The Cockcroft-Gault equation is the pharmacy standard. The trickiest part is choosing the right body weight before plugging in.

FormulasCrCl = [(140 − age) × weight] ÷ (72 × SCr)  × 0.85 if femaleIBW first → actual < IBW use actual; actual > 125% of IBW use AdjBW = IBW + 0.4(actual − IBW); otherwise IBW
Worked example

70-yr-old male, 5'10" (IBW = 73 kg), weighs 90 kg, SCr 1.2. Since 90 < 125% of 73, use IBW. CrCl = (140 − 70) × 73 ÷ (72 × 1.2) = 59.1 mL/min.

Weight rule first, formula second. Using actual weight where AdjBW is required is the classic error.

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Creatinine Clearance
Calculate the creatinine clearance (Cockcroft-Gault) for a 69-year-old male, 5'7" tall, weighing 56 kg, with a serum creatinine of 0.9 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.
mL/min

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10 Creatinine Clearance (Cockcroft-Gault) practice problems with worked solutions

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Problem 1: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 42-year-old female, 5'1" tall, weighing 73 kg, with a serum creatinine of 0.9 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 74 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 1 inches = 47.8 kg.
  2. Choose the weight: Actual BW (73 kg) > 125% of IBW (59.75 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 47.8 + 0.4 × (73 − 47.8) = 57.88 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 42 yr) × 57.88 kg = 5672.24; denominator: 72 × 0.9 mg/dL = 64.8.
  5. 5672.24 ÷ 64.8 ≈ 87.5346; × 0.85 (female) ≈ 74.4 mL/min  (using AdjBW).
  6. Rounded as the question asks: 74 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 2: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 51-year-old female, 5'10" tall, weighing 73 kg, with a serum creatinine of 0.9 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 80 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 10 inches = 68.5 kg.
  2. Choose the weight: Actual BW (73 kg) is between IBW (68.5 kg) and 125% of IBW (85.63 kg) → use IBW = 68.5 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 51 yr) × 68.5 kg = 6096.5; denominator: 72 × 0.9 mg/dL = 64.8.
  5. 6096.5 ÷ 64.8 ≈ 94.0818; × 0.85 (female) ≈ 79.97 mL/min  (using IBW).
  6. Rounded as the question asks: 80 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 3: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 87-year-old female, 5'2" tall, weighing 82 kg, with a serum creatinine of 0.8 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 49 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 2 inches = 50.1 kg.
  2. Choose the weight: Actual BW (82 kg) > 125% of IBW (62.63 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 50.1 + 0.4 × (82 − 50.1) = 62.86 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 87 yr) × 62.86 kg = 3331.58; denominator: 72 × 0.8 mg/dL = 57.6.
  5. 3331.58 ÷ 57.6 ≈ 57.8399; × 0.85 (female) ≈ 49.16 mL/min  (using AdjBW).
  6. Rounded as the question asks: 49 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 4: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 82-year-old male, 5'5" tall, weighing 68 kg, with a serum creatinine of 2.6 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 19 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 5 inches = 61.5 kg.
  2. Choose the weight: Actual BW (68 kg) is between IBW (61.5 kg) and 125% of IBW (76.88 kg) → use IBW = 61.5 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 82 yr) × 61.5 kg = 3567; denominator: 72 × 2.6 mg/dL = 187.2.
  5. 3567 ÷ 187.2 ≈ 19.05 mL/min  (using IBW).
  6. Rounded as the question asks: 19 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 5: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 48-year-old female, 5'1" tall, weighing 65 kg, with a serum creatinine of 0.8 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 74 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 1 inches = 47.8 kg.
  2. Choose the weight: Actual BW (65 kg) > 125% of IBW (59.75 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 47.8 + 0.4 × (65 − 47.8) = 54.68 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 48 yr) × 54.68 kg = 5030.56; denominator: 72 × 0.8 mg/dL = 57.6.
  5. 5030.56 ÷ 57.6 ≈ 87.3361; × 0.85 (female) ≈ 74.24 mL/min  (using AdjBW).
  6. Rounded as the question asks: 74 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 6: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 65-year-old male, 5'7" tall, weighing 78 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 31 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 7 inches = 66.1 kg.
  2. Choose the weight: Actual BW (78 kg) is between IBW (66.1 kg) and 125% of IBW (82.63 kg) → use IBW = 66.1 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 65 yr) × 66.1 kg = 4957.5; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 4957.5 ÷ 158.4 ≈ 31.3 mL/min  (using IBW).
  6. Rounded as the question asks: 31 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 7: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 45-year-old female, 5'3" tall, weighing 46 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 23 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 3 inches = 52.4 kg.
  2. Choose the weight: Actual BW (46 kg) < IBW (52.4 kg) → patient is underweight → use actual BW = 46 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 45 yr) × 46 kg = 4370; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 4370 ÷ 158.4 ≈ 27.5884; × 0.85 (female) ≈ 23.45 mL/min  (using actual BW).
  6. Rounded as the question asks: 23 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 8: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 61-year-old male, 6'1" tall, weighing 125 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 49 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 13 inches = 79.9 kg.
  2. Choose the weight: Actual BW (125 kg) > 125% of IBW (99.88 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 79.9 + 0.4 × (125 − 79.9) = 97.94 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 61 yr) × 97.94 kg = 7737.26; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 7737.26 ÷ 158.4 ≈ 48.85 mL/min  (using AdjBW).
  6. Rounded as the question asks: 49 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 9: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 43-year-old male, 5'9" tall, weighing 57 kg, with a serum creatinine of 1.0 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 77 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 9 inches = 70.7 kg.
  2. Choose the weight: Actual BW (57 kg) < IBW (70.7 kg) → patient is underweight → use actual BW = 57 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 43 yr) × 57 kg = 5529; denominator: 72 × 1.0 mg/dL = 72.
  5. 5529 ÷ 72 ≈ 76.79 mL/min  (using actual BW).
  6. Rounded as the question asks: 77 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 10: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 88-year-old male, 6'0" tall, weighing 91 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 25 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 12 inches = 77.6 kg.
  2. Choose the weight: Actual BW (91 kg) is between IBW (77.6 kg) and 125% of IBW (97 kg) → use IBW = 77.6 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 88 yr) × 77.6 kg = 4035.2; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 4035.2 ÷ 158.4 ≈ 25.47 mL/min  (using IBW).
  6. Rounded as the question asks: 25 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

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