text: RPA is one of several isothermal nucleic acid amplification techniques to be developed as a molecular diagnostic technique, frequently with the objective of simplifying the laboratory instrumentation required relative to PCR.  A partial list of other isothermal amplification techniques include LAMP, NASBA, helicase-dependent amplification (HDA), and nicking enzyme amplification reaction (NEAR).  The techniques differ in the specifics of primer design and reaction mechanism, and in some cases (like RPA) make use of cocktails of two or more enzymes.  Like RPA, many of these techniques offer rapid amplification times with the potential for simplified instrumentation, and reported resistance to substances in unpurified samples that are known to inhibit PCR.  With respect to amplification time, modern thermocyclers with rapid temperature ramps can reduce PCR amplification times to less than 30 minutes, particularly for short amplicons using dual-temperature cycling rather than the conventional three-temperature protocols.  In addition, the demands of sample prep (including lysis and extraction of DNA or RNA, if necessary) should be considered as part of the overall time and complexity inherent to the technique.  These requirements vary according to the technique as well as to the specific target and sample type.
  Compared to PCR, the guidelines for primer and probe design for RPA are less established, and may take a certain degree of trial and error, although recent results indicate that standard PCR primers can work as well. The general principle of a discrete amplicon bounded by a forward and reverse primer with an (optional) internal fluorogenic probe is similar to PCR. PCR primers may be used directly in RPA, but their short length means that recombination rates are low and RPA will not be especially sensitive or fast. Typically 30–38 base primers are needed for efficient recombinase filament formation and RPA performance. This is in contrast to some other techniques such as LAMP which use a larger number of primers subject to additional design constraints.  Although the original 2006 report of RPA describes a functional set of reaction components, the current (proprietary) formulation of the TwistAmp kit is "substantially different"  and is available only from the TwistDx supplier.  This is in comparison to reaction mixtures for PCR which are available from many suppliers, or LAMP or NASBA for which the composition of the reaction mixture is freely published, allowing researchers to create their own customized "kits" from inexpensive ingredients.
  Published scientific literature generally lacks detailed comparison of the performance of isothermal amplification techniques such as RPA, HDA, and LAMP relative to each other, often rather comparing a single isothermal technique to a "gold standard" PCR assay.  This makes it difficult to judge the merits of these techniques independently from the claims of the manufacturers, inventors, or proponents. Furthermore, performance characteristics of any amplification technique are difficult to decouple from primer design: a "good" primer set for one target for RPA may give faster amplification or more sensitive detection than a "poor" LAMP primer set for the same target, but the converse may be true for different primer sets for a different target. An exception is a recent study comparing RT-qPCR, RT-LAMP, and RPA for detection of Schmallenberg virus and bovine viral diarrhea virus, which effectively makes the point that each amplification technique has strengths and weaknesses, which may vary by the target, and that the properties of the available amplification techniques need to be evaluated in combination with the requirements for each application.  As with PCR and any other amplification technique, there is obviously a publication bias, with poorly performing primer sets rarely deemed worthy of reporting.