function calculateREFI() {
var uNa = parseFloat(document.getElementById("urineSodium").value);
var sCr = parseFloat(document.getElementById("serumCreatinine").value);
var uCr = parseFloat(document.getElementById("urineCreatinine").value);
var resultDiv = document.getElementById("refiResultContainer");
var valDiv = document.getElementById("refiResultValue");
var interpDiv = document.getElementById("refiInterpretation");
if (isNaN(uNa) || isNaN(sCr) || isNaN(uCr) || uCr === 0) {
alert("Please enter valid numerical values. Urinary Creatinine cannot be zero.");
return;
}
// Formula: REFI = (Urine Na * Serum Cr) / Urine Cr
var score = (uNa * sCr) / uCr;
var scoreFixed = score.toFixed(2);
valDiv.innerHTML = scoreFixed;
resultDiv.style.display = "block";
if (score < 1) {
interpDiv.innerHTML = "Interpretation: A REFI score of less than 1 typically suggests Prerenal Azotemia. This indicates the kidneys are functioning but receiving inadequate blood flow.";
interpDiv.style.color = "#27ae60";
} else {
interpDiv.innerHTML = "Interpretation: A REFI score of 1 or greater typically suggests Intrinsic Renal Failure, such as Acute Tubular Necrosis (ATN). This indicates potential damage to the kidney structures themselves.";
interpDiv.style.color = "#c0392b";
}
}
Understanding the Renal Failure Index (REFI)
The Renal Failure Index (REFI) is a critical diagnostic metric used by clinicians to differentiate between the various causes of acute kidney injury (AKI). When a patient presents with elevated waste products in the blood, determining whether the cause is a lack of blood flow (prerenal) or direct damage to the kidneys (intrinsic) is essential for proper treatment.
How the REFI Calculation Works
The REFI score is derived by comparing the concentration of sodium and creatinine in the urine against the concentration of creatinine in the blood serum. The specific mathematical formula used in our calculator is:
Clinicians generally categorize REFI results into two primary diagnostic groups:
REFI < 1: Suggestive of prerenal causes. This occurs when the kidneys are healthy but are "starving" for blood, often due to dehydration, blood loss, or heart failure. The kidneys respond by aggressively reabsorbing sodium to maintain volume.
REFI > 1: Suggestive of intrinsic renal causes, most commonly Acute Tubular Necrosis (ATN). In this scenario, the tubules within the kidney are damaged and cannot effectively reabsorb sodium, leading to higher sodium concentrations in the urine.
Example Calculation
Consider a patient with the following lab results:
Urinary Sodium: 12 mEq/L
Serum Creatinine: 2.0 mg/dL
Urinary Creatinine: 60 mg/dL
Using the formula: (12 × 2.0) / 60 = 0.4. Since 0.4 is less than 1, this result points toward a prerenal cause, indicating that the patient may benefit from fluid resuscitation rather than dialysis.
Limitations of the Index
While the REFI is a powerful tool, it should be interpreted in the context of the patient's full clinical picture. Factors such as the use of diuretics (which increase urinary sodium) or pre-existing chronic kidney disease can skew the results. Always consult with a medical professional or nephrologist when reviewing these metrics.