function calculateUrineFlow() {
// Get input elements by ID
var outputEl = document.getElementById('urineOutput');
var timeEl = document.getElementById('collectionTime');
var weightEl = document.getElementById('patientWeight');
var resultBox = document.getElementById('ufrResult');
var hourlyDisplay = document.getElementById('hourlyOutputVal');
var adjustedDisplay = document.getElementById('adjustedOutputVal');
var statusDisplay = document.getElementById('ufrStatus');
// Parse values
var volume = parseFloat(outputEl.value);
var hours = parseFloat(timeEl.value);
var weight = parseFloat(weightEl.value);
// Validate inputs
if (isNaN(volume) || isNaN(hours) || isNaN(weight) || hours <= 0 || weight <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Calculation Logic
// 1. Calculate mL per Hour
var mlPerHour = volume / hours;
// 2. Calculate mL per kg per Hour (The standard medical metric)
var mlKgHr = mlPerHour / weight;
// Display Results
hourlyDisplay.innerHTML = mlPerHour.toFixed(1) + " mL/hr";
adjustedDisplay.innerHTML = mlKgHr.toFixed(2) + " mL/kg/hr";
// Clinical Interpretation Logic
// Standard adult reference: 0.5 – 1.0 mL/kg/hr is average/target.
// 2.5 – 3.0 mL/kg/hr suggests Polyuria (context dependent).
var statusText = "";
var statusClass = "";
if (mlKgHr = 0.5 && mlKgHr <= 2.5) {
statusText = "Within Normal Range";
statusClass = "status-normal";
} else {
statusText = "POLYURIA (High Output)";
statusClass = "status-high";
}
// Update status box
statusDisplay.innerHTML = statusText;
statusDisplay.className = "ufr-alert " + statusClass;
// Show result container
resultBox.style.display = "block";
}
Understanding Urine Flow Rate Calculation
Monitoring urine output is a fundamental aspect of assessing kidney function and fluid balance in clinical settings. The Urine Flow Rate (UFR) is a critical vital sign, often referred to as the "fifth vital sign" in nephrology and critical care. It helps healthcare professionals detect early signs of Acute Kidney Injury (AKI), dehydration, or fluid overload.
While total volume is important, the most clinically significant metric is the weight-adjusted urine output, measured in milliliters per kilogram per hour (mL/kg/hr). This normalization allows for accurate comparison across different patient sizes, from pediatrics to adults.
The Formula
To calculate the Urine Flow Rate manually, you need three data points: the total volume of urine collected, the duration of the collection, and the patient's body weight.
Step 1: Calculate Hourly Rate Hourly Output = Total Urine Volume (mL) ÷ Collection Time (hr)
Interpreting the results requires knowledge of standard physiological thresholds. While specific targets may vary based on patient condition (e.g., burn victims require higher output), the general guidelines for adults are:
Normal Output: 0.5 to 1.5 mL/kg/hr. This indicates adequate renal perfusion.
Oliguria: Less than 0.5 mL/kg/hr. This is a "warning zone" often indicating dehydration, shock, or early kidney failure. If this persists for more than 6 consecutive hours, it meets the criteria for AKI stage 1.
Anuria: Less than 50-100 mL over 24 hours (effectively 0 mL/kg/hr). This represents kidney failure or obstruction.
Polyuria: Generally greater than 2.5 or 3.0 mL/kg/hr. This may result from diuretic use, diabetes insipidus, or post-obstructive diuresis.
Example Calculation
Consider a patient weighing 80 kg. The nurse empties the catheter bag after 4 hours and records 240 mL of urine.
First, find the hourly rate: 240 mL ÷ 4 hours = 60 mL/hr.
Next, divide by weight: 60 mL/hr ÷ 80 kg = 0.75 mL/kg/hr.
Since 0.75 is greater than 0.5, the patient's urine output is considered adequate. Conversely, if the same patient only produced 100 mL in 4 hours, the rate would be roughly 0.31 mL/kg/hr, indicating oliguria.
Why is Precision Important?
Inaccurate calculation of urine flow rates can lead to missed diagnoses of AKI or inappropriate fluid resuscitation. In pediatric patients, where small volumes matter significantly, precise measurement (often weighing diapers) and calculation down to the decimal point is mandatory for safe care.