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Q1
Is it necessary to dilute samples before measurement?
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A1
Dilution is not always required. However, when L-FABP concentration exceeds 400 ng/mL, please dilute with a Standard Diluent (0 ng/mL), and then re-measure.
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Q2
Is it necessary to adjust urinary L-FABP concentration with urinary creatinine correction?
What is the conversion formula for creatinine correction?
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A2
In principle, urinary creatinine correction is necessary to prevent errors in urinary concentration. However, the result obtained with our L-FABP POC kits, determines by L-FABP concentration in urine.
In the case of AKI (Acute Kidney Injury), the urinary creatinine level itself may fluctuate significantly, so the concentration of the urinary L-FABP measurement is also reported, and the actual or corrected value is used at the discretion of the doctor.
Conversion Formula
L-FABP (ug/g･Cr) = L-FABP (ng/mL) ÷ Cr (mg/dL) × 100
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Q3
When is the optimal time for taking urine samples for measurement?
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A3
Urinary L-FABP can be measured in early morning urine, spot urine and pooled urine. However, it is desirable to prepare samples under the same conditions in monitoring L-FABP levels.
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Q4
What are the methods for storing and stabilizing samples?
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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 samples by refrigeration, please make your measurements within 48 hours.
*If refrigeration is difficult, please use a coolant or similar.
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Q5
Is there anything to be careful about in the freezing and thawing of samples?
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A5
Thawing of frozen samples (at -80℃) will not affect the assay value. However, repeated freeze-thaw cycles should be avoided.
*It is recommended to store samples in small portions. After thawing, samples may become cloudy, but measurement is still possible. If the sample is centrifuged and the cloudiness is cleared, it will not affect the assay result.
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Q6
Is there any influence on measurement when preservative is added to accumulated urine (samples)?
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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.
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Q7
Are there diurnal rhythm variations in urinary L-FABP levels?
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A7
Variations may be observed within the normal range of L-FABP levels.
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Q8
Are there any effects on interference substances?
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A8
Yes. The presence of bilirubin, hemoglobin, glucose or ascorbic acid in urine sample can affect the performance of ELISA Kit. However, the following levels do not influence on measurement value:
- 1. Free bilirubin up to 19.7 mg/dL.
- 2. Conjugated bilirubin up to 21.8 mg/dL.
- 3. Hemolytic hemoglobin up to 24.4 mg/dL.
- 4. Glucose up to 45.0 mg/mL.
- 5. Ascorbic acid up to 12.5 mg/mL.
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Q9
Does the contrast media for angiography have any effect on measurements?
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A9
The timing of clearance of the contrast medium into the urine has no effect on ELISA values (no baseline inhibition). The increase in urinary L-FABP is not due to nephrotoxicity of the contrast agent itself, but rather to a decrease in micro-renal blood flow (renal vasoconstriction) caused by the contrast agent.
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Q1
Is it necessary to dilute samples before measurement?
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A1
Dilution of samples is not needed.
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Q2
When is the optimal time for taking urine samples for measurement?
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A2
Urinary L-FABP can be measured in early morning urine, spot urine and pooled urine, except for acid pooled urine. However, it is desirable to prepare samples under the same conditions in monitoring L-FABP levels.
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Q3
Which is the optimal sample condition for measurement?
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A3
Urinary L-FABP can be measured fresh urine and stored urine in refrigerator and freezer.
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Q4
How is urine sample stability at room temperature?
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A4
If stored at room temperature up to 8 hours, the effect on the results should be negligible. In rare cases, urine samples containing high concentrations of L-FABP (several hundred ng/mL) have been found to have persistently elevated L-FABP levels, so the package insert recommends that urine samples be measured as soon as possible after collection.
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Q5
Does the foreign substance in the sample have any effect on measurement systems?
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A5
Correct results may not be obtained if the sample is contaminated with foreign matter or is cloudy. Before mixing with the pretreatment, centrifuge or allow to let rest sample in the dark at room temperature for at least 30 minutes and slowly collect 100 µL of specimen from the supernatant to avoid aspiration of foreign matter. The red blood cells (haematuria), cell detachment due to infection or inflammation, and glomerular and tubular tissue shedding can be listed as foreign matters.
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Q6
Can viscous sample be measured?
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A6
Viscous urine samples may not spread through the membrane and may stop or flow at a much slower rate than normal. The RENISCHEM L-FABP ELISA quantification kit is recommended for such samples as it is not possible to obtain correct results.
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Q7
Are there any effects on interference substances?
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A7
Yes. The presence of bilirubin, hemoglobin, glucose or ascorbic acid in urine sample can affect the performance of POC Kit. However, the following levels do not influence on measurement value:
- 1. Free bilirubin up to 19.7 mg/dL.
- 2. Conjugated bilirubin up to 21.8 mg/dL.
- 3. Hemolytic hemoglobin up to 97.4 mg/dL.
- 4. Glucose up to 1000 mg/dL.
- 5. Ascorbic acid up to 1.6 mg/mL.
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Q8
Can colored sample be measured?
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A8
If there is dark coloration on urine sample, it may not give a correct result. For example, if urine from a patient on rifampicin medication is measured with the POC, the entire membrane of POC kits strip will be stained orange, which will be in contrast to the color of the test line and may give a false result. (See pictures below) Hematuria may also stain the membrane. If a correct result is not obtained, it is recommended to re-collect sample at a time when it is not affected by medication and to test with POC kit again or to use RENISCHEM
® L-FABP ELISA kit for obtaining quantitative results.
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Q9
Can the sample of patient with end stage renal failure (stage 4 of diabetic nephropathy or end stage kidney disease) be measured?
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A9
Yes, in diabetic nephropathy of type 2 diabetic patients study which consists in measurement according to the different stage of disease(stage 1 to 4), shows that urinary L-FABP levels are correlated with the progression of diabetic nephropathy. So it is possible to measure urinary L-FABP in the stage renal failure. (Diabetes Care 34:691-696, 2011.
PubMed▶)
