Calculator Form
Use estimated, measured, or both methods. The form uses a three column layout on large screens, two columns on smaller screens, and one column on mobile.
Example Data Table
| Case | GA | Weight | Length | SCr | k | Estimated CrCl |
|---|---|---|---|---|---|---|
| Term day 3 infant | 39 weeks | 3.2 kg | 50 cm | 0.70 mg/dL | 0.45 | 32.14 mL/min/1.73 m² |
| Preterm day 5 infant | 31 weeks | 1.5 kg | 41 cm | 0.90 mg/dL | 0.33 | 15.03 mL/min/1.73 m² |
| Term infant with lower SCr | 40 weeks | 3.6 kg | 52 cm | 0.50 mg/dL | 0.45 | 46.80 mL/min/1.73 m² |
Formula Used
The bedside estimate uses a neonatal length based constant. The measured method uses a timed urine collection. The calculator also reports absolute clearance using the entered or calculated body surface area.
Estimated CrCl (mL/min/1.73 m²) = k × Length (cm) ÷ Serum Creatinine (mg/dL)
Measured CrCl (mL/min) = Urine Creatinine (mg/dL) × Urine Flow (mL/min) ÷ Serum Creatinine (mg/dL)
Urine Flow (mL/min) = Collected Urine Volume (mL) ÷ Collection Time (minutes)
Measured CrCl normalized = Measured CrCl × 1.73 ÷ Body Surface Area (m²)
Estimated absolute CrCl = Estimated CrCl × Body Surface Area ÷ 1.73
Mosteller BSA (m²) = √[Length (cm) × Weight (kg) ÷ 3600]
Default constants used here are 0.45 for term neonates and 0.33 for preterm neonates. A custom constant can be entered when local policy or published protocol differs.
How to Use This Calculator
- Choose estimated, measured, or both methods.
- Select the neonate type or enter a custom k factor.
- Enter gestational age, postnatal age, weight, length, and serum creatinine.
- For measured clearance, also enter urine creatinine, total urine volume, and collection duration.
- Leave body surface area blank to let the calculator derive it automatically from length and weight.
- Press Submit to show the results under the header and above the form.
- Review the graph, notes, and interpretation band, then export the summary as CSV or PDF when needed.
Frequently Asked Questions
1) What does this calculator estimate?
It estimates neonatal creatinine clearance from serum creatinine and body length, and it can also calculate measured clearance from timed urine collection data. The output helps frame renal function, trending, and medication review.
2) Which equation is used for the bedside estimate?
The bedside estimate uses a neonatal Schwartz style relationship: k multiplied by length in centimeters, divided by serum creatinine in mg/dL. The k constant changes with term or preterm selection, or it can be customized.
3) When should I use the measured method?
Use the measured method when you have a reliable timed urine collection and urine creatinine value. It is helpful when the bedside estimate seems inconsistent with clinical status or when close renal monitoring is needed.
4) Why can neonatal serum creatinine be hard to interpret early?
During the first days after birth, serum creatinine may still reflect maternal creatinine and rapid physiologic change. That is why serial values, urine output, gestational age, and overall condition matter more than a single isolated number.
5) What k value should I choose?
This file uses 0.45 for term neonates and 0.33 for preterm neonates. Use the custom option when your service follows a different validated constant, research protocol, or local dosing guidance.
6) Why are results shown as normalized and absolute values?
Normalized values allow comparison across body sizes by indexing to 1.73 m². Absolute values reflect the infant’s actual size and can be useful when interpreting true clearance capacity in very small patients.
7) Does this calculator replace clinical judgment?
No. It is a support tool. Drug dosing, kidney injury assessment, and fluid decisions still require clinical examination, laboratory trends, urine output, and neonatal specialist judgment.
8) What if estimated and measured results disagree?
First review urine collection completeness, sampling timing, and the selected k factor. Then compare with repeat creatinine values, urine output, fluid balance, and the infant’s clinical trajectory before changing treatment plans.