About L-FABP

FAQ

About L-FABP

Samples, measurement

Product performance/operation

Research use

About L-FABP

Q1. What are L-FABPs?
A1. L-FABP is an abbreviation for “Liver-type Fatty Acid Binding Protein,” and L-FABPs are fatty acid binding proteins 14-15 kDa in molecular weight that are specifically produced in the liver and kidney proximal tubules. Because L-FABPs are substances derived from the cytoplasm of the renal proximal tubules and are excreted in urine due to renal tubular ischemia and oxidation stress on renal tubules, urinary L-FABPs are useful for early diagnosis of renal disease accompanying tubular dysfunction.
Q2. Are liver-derived L-FABPs excreted in urine?
A2. When nephropathy occurs, and L-FABPs excreted from the liver are no longer reabsorbed by the kidneys, they are excreted in urine. (Accordingly, in the absence of nephropathy, L-FABPs excreted from the liver are reabsorbed by the kidneys, so they hardly appear at all in urine.)
In the case of hepatitis fulminant or hepatorenal syndrome, approximately 15% of urinary L-FABPs originate in the liver, but these can be easily discerned through joint use with other biomarkers.
Q3. How are L-FABPs different from urinary albumin?

A3. Urinary albumin is a glomerular injury marker that indicates the result of filtration function failure. The quantity excreted in the urine increases as the glomerular injury progresses. In contrast, L-FABPs are markers reflecting tubular dysfunction, and are excreted in the urine in response to ischemia and oxidation stress.

Samples, measurement

Q1. Is dilution of samples required before measurement?
A1. Dilution is not always required.
For samples with an L-FABP concentration in excess of 400 ng/mL, please dilute in a Standard Diluent (0 ng/mL), and then re-measure.
Q2. Is urinary creatinine correction required? What is the conversion formula for creatinine correction?

A2. In principle, urinary creatinine correction is necessary to prevent urinary concentration errors.

Conversion Formula

L-FABP (ug/g・Cr) = L-FABP (ng/mL) ÷ Cr (mg/dL) × 100

However, in instances of acute kidney injury (AKI), because the values for urinary creatinine itself may fluctuate greatly, the concentrations of urinary L-FABP values are also reported, and doctors use their judgment as to whether to use actual values or creatinine corrected values.
Q3. When is the optimal time for taking urine samples for measurement (first urination early in the morning, any-time sampling, accumulated sampling)?
A3. Urinary L-FABPs can be measured from samples taken in any of those ways. However, when monitoring, it is desirable to prepare sample conditions.
Q4. What are the methods for storing and stabilizing samples?
A4. Please store samples either by refrigeration (4 degrees Celsius) or freezing (-20 to -30 degrees Celsius, -80 degrees Celsius).
Stability has been confirmed for up to 48 hours (2 days) when storing by refrigeration (4 degrees Celsius), and up to one (1) year when storing by freezing (-80 degrees Celsius). When storing by refrigeration please make your measurements within 48 hours.
*If refrigeration is difficult, please use a coolant or similar.
Q5. Is there anything to be careful about in the freezing and thawing of samples?

A5. Thawing a sample saved by freezing (-80 degrees Celsius) and then taking measurements will have no effect on the measured values.
However, please avoid repeated freezing and thawing.
*Where possible, storage after splitting samples into smaller portions is recommended.

Also, samples may be cloudy after thawing, but measurement is still possible. Dispersing cloudiness in samples by centrifugal separation and then taking measurements will have no effect on the measured values.
Q6. Are measurements influenced when preservative is added to accumulated urine (samples)?
A6. Adding hydrochloric acid can sometimes have an effect (values tend to be lower than original L-FABP values) on measurements. The addition of sodium azide or toluene has no effect on measurements.
Q7. Are diurnal rhythm variations in urinary L-FABP levels recognized?
A7. Variations that encompass different reference values are not recognized.
Q8. Are there any effects on coexistent substances?
A8. 1. Free form bilirubin: No effect on measurements recognized up to 19.7 mg/dL.
2. Conjugated bilirubin: No effect on measurements recognized up to 21.8 mg/dL.
3. Hemolytic hemoglobin: No effect on measurements recognized up to 24.4 mg/dL.
4. Glucose: No effect on measurements recognized up to 45.0 mg/mL.
5. Ascorbic acid: No effect on measurements recognized up to 12.5 mg/mL.
Q9. Does the contrast media of angiography have any effect on measurement systems?
A9. With the timing of the clearance when the contrast media appears in urine, the measurement values of the urinary L-FABP baseline are not affected by the contrast media. A rise in urinary L-FABP after an angiography is not because of nephrotoxicity in the contrast media itself, but is considered to be because renal microvascular flow decrease (caused by the renal vascular spasm) occurs due to the contrast media.

Product performance/operation

Q1. Please tell us about the product.
A1. ・Qualitative or quantitative? → L-FABP ELISA kits are Quantitative test. L-FABP POC kit is for semi-quantitative assay.
・Automatic or manual test method? → Manual test method
・Simple kit able to be used bedside? → L-FABP POC kit is used at bedside. If quantitative assay result is needed, please use L-FABP ELISA kits.
Any devices required for measurement? → L-FABP requires a separate plate reader that measures absorbance. L-FABP POC does not need any readers.
Q2. Please tell us about the measurement principle.
A2. More information can be found by following the below link:
Measurement principle (ELISA method)
Measurement principle (POC)
Q3. Please tell us about the product’s component chemical reagents.
A3. More information can be found by following the below link:
Product composition
Q4. Please tell us about product storage and shelf-life.
A4. L-FABP ELISA kit:
   Store between 2~8°C(avoid freezing)
   Shelf life:12 months (expiry date written on outside of box)
L-FABP POC kit:
   Store between 1~30°C (avoid freezing)
   Shelf life: 12 months (expiry date written on outside of box)

Research use

Q1. Are there any kidney injury markers that should be investigated in comparison with L-FABPs?
A1. NAG and urine protein (urinary albumin) are recommended.
Q2. Is measurement possible on biopsy samples such as human kidney tissue?
A2. It depends on the quantity of tissue, but measurement of homogenated crushed liquid filtrate preprocessed the same way as for ELISA is possible. However, the product cannot guarantee performance in that area, as it is a kit for the purpose of the measuring urinary L-FABPs.
Q3. Can L-FABPs in the blood be measured?
A3. Yes, they can.
However, the product cannot guarantee performance in that area, as it is a kit (product) for the purpose of the measuring urinary L-FABPs. Furthermore, the stability of L-FABPs in the blood and normal upper limit values are unclear.
Q4. How should research using mice be approached?
A4. Due to expression of urinary L-FABP being suppressed in rodents (mice, rats, etc.), it is necessary to use human-type L-FABP transgenic mice. Please direct inquiries concerning the use of Tg mice to Charles river laboratories Japan, inc.
Q5. Is it possible to receive technical instruction on taking measurements?
A5. Detailed instructions can be found by following the below links:
Standard
Measurement

Download product leaflet

How to use RENISCHEM® L-FABP POC kit

For nonclinical safety evaluation

Urinary L-FABP kits for Rat, Dog, Cat, Monkey and Pig are available for the purpose of monitoring drug nephrotoxicity and drug effectiveness.
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