Suggest to rephrase - PREVIOUS QUESTION was How do I modify test parameters?
SAQ:
- Can I create and save custom test protocols?
- How can I customize test methods?
- How to adapt methods for specific sample types?
- Are there limitations to method customization?
Method
During the incubation run, images are captured and analyzed. The color of each cup is expressed in a so-called Zvalue. During the incubation run, DAS continuously measures the Z-value of each cup and if enough cups have reached a certain level, the incubation is stopped. A cup is defined positive or negative on the base of its Z-value at the end of the incubation. This analysis approach is called “method”. Each Delvotest® product has its own characteristics and therefore each product has its own method. The settings of each method can be viewed and adjusted at the Settings page (it is required to log in).
Settings
From the browser page Click on the header “Sign in” and sign in under “Administrator” and provide the password 'Admin'.
• Page will be refreshed, with more options. Click on the header “Settings”
• Hoover the field name to see the related tooltip
• After filling the fields click “Save As” to save the new method or “Update” to save a modified method.
DSM method
DSM has validated a defined method for each Delvotest® presentation and these are called “DSM method” and these methods cannot be adjusted. Nevertheless, it is possible to adjust the setting of a method or create a new method and use it instead of the DSM one.
Default method
When the barcode of a plate is scanned, the DAS automatically selects a method for this plate (it recognizes the type of product). In this page it can be defined which method will be selected as the default method for a certain product. Only one method can be defined as the default method for each product.
Product
Select the type of plate to be used for this method.
Temperature
The temperature affects the speed of the test and therefore the incubation temperature is set by the method.
Stop criteria
During the incubation run, “negative” cups should change in color, while for “positive” this color change goes much slower. DAS continuously checks the color of the cups and determines if the color change is large enough to stop the incubation. DAS calculates for each cup a Z-value and it determines a group of cups, which have the largest color change (lowest Z-value). From this group, the highest Z-value (slowest of the fastest group) is selected and this value is called “Leader”. If the leader has reached a certain level (field Z-value negative well at control time), the incubation is stopped (this moment is called control time).
The size of the group is determined by a percentage (“Perc negative well”, DSM methods use 10%) of the total number of cups incubated or a minimum number (“Minimum nr negative wells”, DSM methods use 4). Therefore, in case of single strip incubation, at least 4 wells need to be filled with raw milk. For this reason, it is required that at least 40% of the cups of the incubated plate contains expected negative samples. The figure below illustrates how is determined to stop the incubation.
Incubation time
In general, the incubation run will be stopped by the stop criteria. If somehow the stop criteria are not met, the incubation run will stop at the maximum time (“maximum incubation time”). DAS checks if the performed incubation time is within certain limits (“expected minimum incubation time” and “expected maximum incubation time”) and warning is generated when outside the range.
Invalid cup detection
The figure above shows the expected profile of the Z-value in time. If the content of a cup is “incorrect” (e.g. sour milk) the measured Z-values will be different. DAS can detect such unexpected behavior and classify a cup as invalid. An invalid cup is treated differently as the other cups and it will not be used for the determination of the control time.
• For valid cups holds that the Z-value of a cup from start of incubation till a certain “check time” (field Check time valid well (min)) is within a certain range (fields Valid well maximum Z-value, Valid well minimum Z-value).
• A cup with a Z-value lower than the defined range is labeled as “Too Fast, FST”.
• A cup with a Z-value higher than the defined range is labeled as “Incorrect Color, INV”.
Classification
From time=0 till check time, it is verified if a cup is considered as valid or invalid. Invalid cups are not classified and get the label “invalid”. At control time valid cups are classified as following:
• Cup is classified as positive if Z-value at control time is larger than “Z-value positive”
• Cup is classified as negative if Z-value at control time is smaller than “Z-value negative”
• Otherwise, cup is classified as Undefined or doubtful
Positive, negative references
Procedures can demand that an incubation run is always executed with a number of positive references or negative references in a plate. This requirement can be set in the method and DAS will check at the start of an incubation run, if a plate contains minimally the required number of references. If the plate has too few references, the incubation run cannot be started. An operator must assign the reference in the layout definition (see also 'Layout-definition).
Note: the method only checks on the number of references, but it does not treat the reference cups differently than the other cups.