EDUCATION CENTER - Additional Info on Value Ranges

fBhCG First Trimester Expected Range View PDF

Regarding your ELISA kit for determination of Free Beta hCG (2025-300), do you have expected median value for this marker from 8 to 14 week of pregnancy?

We can only provide a copy of reference ranges from the British Journal of Obstetrics and Gynecology below which although is not Monobind's products, we would expect comparable results. A graph of the median values and the 5 and 95th percentile for free beta is given

EDUCATION CENTER - Lab Tips

Pipetting Techniques & Recommendations View PDF

As presented in every Monobind product insert, the micropipette is a required material to perform an immunoassay. Its proper use will contribute to the accuracy of test results including values found for patient samples. Therefore it is important for both labs managers and technicians to have a firm understanding of the instrument. Specifically, these parties should be aware of the design characteristics and variations, techniques for use and the importance of scheduled calibration and maintenance.

To develop an understanding of the micropipette, the general construction is shown in Figure 1. While some design elements do vary, every pipette has a plunger button, tip ejector button, and tip ejector arm. The greatest distinction in design is found between fixed and variable-volume dispensing pipettes wherein users may specify a set volume. Additional design differences are present among manufactures and models.

Even with the common design elements (plunger button, tip ejector, etc), function will vary between pipettes so users must appreciate the specifics of their micropipette to ensure proper usage. A first interaction may involve users depressing the plunger button and experiencing the force required to do so. They will likely notice moving from the rest position to the first stop requires less force than moving to the second stop. The purpose of this design is to differentiate the plunger positions. Figure 2 shows the typical function of a micropipette plunger button. Remember manufacturers may utilize different approaches to design. Given the differences, it is very important to select a micropipette based on the needs of the laboratory and thereby technician. Before selecting suitable equipment, one must have an understanding of dispensing techniques. The following offers a discussion of dispense modes to help form the decision maker’s opinion of available micropipettes and the training of users’ technique.

Forward-mode dispensing is considered the "standard mode" by most pipette manufacturers. This mode begins at rest and continues to the first stop to initiate the pick-up of solution. The plunger is then released back to the rest position and the solution is aspirated (drawn) into the tip. To dispense the solution, the plunger must be depressed to the second stop which will release the set volume. Each step of this method is shown in Scheme 1.

Although forward-mode dispensing is considered the standard mode, a few draw backs accompany the method. Technician fatigue is on top the list due to the extra force required to depress the plunger button to the second stop. Another significant disadvantage is a high incidence of inaccuracy since only the set volume is aspirated into the tip. Surface tensions will cause some solution to adhere inside the tip resulting in an inaccurate dispensing volume.

Reverse-mode offers another dispending option. In this technique, the initial aspiration of the sample requires depressing the plunger to the second stop then releasing to the rest position. From this point the sample is dispensed by depressing the plunger to the first stop. After dispensing, a portion of the sample remains in the tip because aspiration from the second stop draws slightly more solution than the set volume. Scheme 2 shows the steps taken when dispensing in the reverse-mode.

This "Reverse-Mode" technique is considered by Monobind to offer more advantages than disadvantages when performed properly. The main draw-back for users is it requires slightly more sample or reagent than needed by the assay. However, if ample volume exists, the method produces superior accuracy which is a critical benefit to laboratories. Reverse-mode technique also lessens fatigue when technicians dispense the same solution multiple times since subsequent pick-ups only require releasing the plunger from the first stop to rest position. The force required between these is much less than in reaching the second stop as necessary to dispense in forward mode. For these reasons, Monobind recommends the reverse-mode pipetting technique to users.

In addition to selecting equipment and utilizing preferred techniques, labs must ensure micropipettes are properly calibrated. Good clinical laboratory practices include equipment calibration and maintenance schedules that must be performed by qualified parties whom issue compliance certificates. Such quality records are valid for a set period and must be renewed accordingly.

A final matter to consider is how dispensing techniques influence laboratory automation. The same surface tension conditions exists affecting volume accuracy in automated dispensing. Therefore when evaluating automation, one must inquire about the dispensing capabilities related not only to accuracy and precision concerns but also to the available dispense modes.

Monobind’s Autoplex instrument uses in effect reverse-mode dispensing (extra volume pick-up of samples > 25 µl) and has been tested rigorously for pipetting accuracy via Within Assay Precision (%CV of running duplicates in different positions on the plate) and Reproducibility of Response Variable (%CV of running duplicates in adjacent wells). With Autoplex, labs receive a Monobind certified system, optimized analytics and preprogrammed applications for AccuBind and AccuLite reagents.

Learn more at http://www.monobind.com/instruments/autoplex