Renal Indices (FENa, RFI)
Norm of Renal Indices (FENa, RFI)
Norm not applicable. Indices are used only for clients experiencing or suspected of experiencing renal failure.
Renal Indices: Differentiating Categories of Renal Failure
Fractional Excretion of Sodium in Urine (Urine Na+× Serum Creatinine × 100)/ (Serum Na+× Urine Creatinine) |
Urine Sodium |
Renal Failure Index: Urine Na+× (Plasma Creatinine/Urine Creatinine) |
|
| Prerenal and volume depletion | <1% | <20 mmol/L | <1% |
| Renal (acute tubular necrosis) | >1% | >40 mmol/L | >1% |
| Postrenal | >4% |
Usage of Renal Indices (FENa, RFI)
Determination of the category of renal failure; ongoing monitoring during recovery from acute tubular necrosis.
Description of Renal Indices (FENa, RFI)
Both renal indices are mathematically calculated values of renal sodium handling, using laboratory measurement results. Urinary sodium levels are used in conjunction with urine and plasma or serum creatinine levels in two formulas that help narrow down the source of renal failure into prerenal, renal, and postrenal causes. Both the fractional excretion of sodium in urine (FENa) and the renal failure index (RFI) determine how well the kidneys are able to remove urine from the blood into the urine. They are expressed as the percentage of serum sodium that is excreted in the urine.
Professional Considerations of Renal Indices (FENa, RFI)
Consent form NOT required.
Preparation
- Obtain a clean-catch urine container, towelettes, and a red-topped tube. For pediatric/infant collections, also obtain tape and a pediatric urine collection device/bag.
Procedure
- Obtain a clean-catch urine sample and a 3-mL blood sample.
- Pediatric/infant specimen collection:
- a. The child is placed in a supine position with the knees flexed and the hips externally rotated and abducted.
- b. Cleanse, rinse, and thoroughly dry the perineal area.
- c. To prevent the child from removing the collection device/bag, a diaper may be placed over the genital area.
- d. Females: Tape the pediatric collection device/bag to the perineum. Starting at the area between the anus and vagina, apply the device/bag in an anterior direction.
- e. Males: Place the pediatric collection device/bag over the penis and scrotum and tape it to the perineal area.
- f. Empty the collection bag into the refrigerated collection container after the infant or child voids.
Postprocedure Care
- Remove the collection device/bag by gently peeling it away from the skin.
Client and Family Teaching
- None.
Factors That Affect Results
- Both tests are most useful when urine output is oliguric.
Other Data
- None.
