Troubleshooting / Common Issues
Sensitivity Status is Insensitive — ULNR is above all data points
Possible causes
- –ULNR is set higher than appropriate (verify the normal range calculation)
- –The reagent lot is genuinely insensitive to the specific factor being tested
- –RAF is incorrect, causing actual dilutions to be shifted lower than intended
- –Insufficient dilution range — the lowest dilution tested may not produce a long enough clotting time
Recommended action
First verify the ULNR value and normal range study. Then confirm the RAF from the package insert. Consider extending the dilution range to lower percentages (e.g., 10%–20%) to determine if an abnormal clotting time can be produced at all. If the reagent remains insensitive, contact the manufacturer.
Sensitivity Status is Hypersensitive — ULNR is below all data points
Possible causes
- –ULNR is set lower than appropriate (verify the normal range calculation)
- –The reagent is genuinely hypersensitive and flags even high factor activity as prolonged
- –RAF is incorrect, causing actual dilutions to be shifted higher than intended
Recommended action
Verify the ULNR from the normal range study. Confirm that the normal range was established using the correct reagent lot and analyzer. If the ULNR is correct and all dilutions produce clotting times above it, the reagent may be hypersensitive — consult the manufacturer's specification for expected sensitivity ranges.
Low R² or poor curve fit
Possible causes
- –Regression type does not match the shape of the dose-response relationship
- –Polynomial degree too low (linear when the response is clearly curvilinear)
- –Outlier data points at extreme dilutions distorting the fit
- –Regression range is too wide, including dilutions where the relationship is nonlinear
Recommended action
Try switching regression types (polynomial vs. logarithmic) or adjusting the polynomial degree. Narrow the regression limits to focus on the 20%–75% dilution range. Check whether any specific dilution level has unusually high clotting time variability across replicates, which may indicate a sample preparation issue.
Large discrepancy between First Abnormal Dilution and Calculated Sensitivity
Possible causes
- –Sparse dilution levels near the ULNR crossover — the step size between tested levels is too coarse
- –Poor regression fit in the ULNR crossover region
- –Actual dilutions are bunched in one part of the range with a gap near the sensitivity threshold
Recommended action
Add additional dilution levels in the range where the regression curve is expected to cross the ULNR. This improves resolution for both the First Abnormal Dilution and the regression fit. The default 8-dilution design (25%–70%) may not have adequate resolution if the sensitivity falls near the edges of the tested range.
Calculated Sensitivity cannot be determined
Possible causes
- –Sensitivity status is Insensitive or Hypersensitive — the ULNR does not fall within the regression range
- –The regression curve does not intersect the ULNR within the tested dilution range
Recommended action
If the status is Insensitive, the regression curve never reaches the ULNR within the tested dilutions. Extend the dilution range to lower percentages. If Hypersensitive, all tested dilutions already exceed the ULNR — consider whether the ULNR is correctly configured or whether this represents a genuinely hypersensitive reagent.