Final answer:
The creatinine clearance (CrCl) for a 40-year-old woman weighing 140 lbs and having a serum creatinine of 0.89 mg/dL can be calculated using the Cockcroft-Gault equation. Her weight is first converted to kilograms, and then the values are plugged into the equation appropriate for women. This test estimates kidney function based on glomerular filtration rate.
Step-by-step explanation:
Calculating Creatinine Clearance
To calculate the creatinine clearance (CrCl) for a 40-year-old woman who weighs 140 pounds, is 5 feet 5 inches tall, and has a serum creatinine (SCr) of 0.89 mg/dL, we use the Cockcroft-Gault equation. The CrCl is an indicator of the glomerular filtration rate (GFR), which reflects kidney function. This equation takes into consideration age, weight, gender, and serum creatinine levels.
First, convert the weight from pounds to kilograms:
140 lbs × 0.453592 = 63.5 kg
Then, use the Cockcroft-Gault equation specifically for women:
Cockcroft-Gault formula for women: [[(140 - age) × weight (kg)] / (72 × SCr)] × 0.85
Plugging in the values, we get:
[[ (140 - 40) × 63.5] / (72 × 0.89)] × 0.85 = CCr-corrected
Note that in clinical practice, the CrCl is often reported relative to body surface area (BSA) which averages to 1.7, to provide a standard clearance rate, but for this calculation, we are focusing on using actual body weight.
Interpreting the Results
A normal creatinine clearance value for an adult female less than 40 years old is 80-125 ml/min. After the age of 40, this normal range decreases by about 6.5 ml/min for each decade of life. Hence, knowing the individual's CrCl can help to determine if there is impairment in their kidney function.