Editing Assay (section)

==Assay types based on the nature of the assay process==
===Time and number of measurements taken===
Depending on whether an assay just looks at a single time point or timed readings taken at multiple time points, an assay may be:
#An '''end point assay''', in which a single measurement is performed after a fixed incubation period; or
#A '''kinetic assay''', in which measurements are performed multiple times over a fixed time interval. Kinetic assay results may be visualized numerically (for example, as a slope parameter representing the rate of signal change over time), or graphically (for example, as a plot of the signal measured at each time point). For kinetic assays, both the magnitude and shape of the measured response over time provide important information.
#A '''high throughput assay''' can be either an endpoint or a kinetic assay usually done on an automated platform in 96-, 384- or 1536-well microplate formats ('''High Throughput Screening'''). Such assays are able to test large number of compounds or analytes or make functional biological readouts in response to a stimuli and/or compounds being tested.<ref>{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK343428/ |title=Assay Guidance Manual [Internet] |last1=Sittampalam |first1= GS|date=2004 |website=ncbi.nlm.com |publisher=Eli Lilly & Company and the [[National Center for Advancing Translational Sciences]] |access-date= 12 Aug 2016}}</ref>

===Number of analytes detected===
Depending on how many targets or analytes are being measured:
#Usual assays are simple or ''single target assays'' which is usually the default unless it is called multiplex.
#[[Multiplex assay]]s are used to simultaneously measure the presence, concentration, activity, or quality of multiple analytes in a single test. The advent of ''multiplexing'' enabled rapid, efficient sample testing in many fields, including immunology, cytochemistry, genetics/genomics, pharmacokinetics, and toxicology.<ref>{{cite web |url=http://www.biotek.com/resources/articles/multiplexed-assays-life-sciences.html |title=Multiplexed Assays in the Life Sciences |last1= Banks|first1= Peter |date=7 Jun 2010 |website= biotek.com|publisher=[[BioTek]] Instruments Inc |access-date= 13 Aug 2016}}</ref>

===Result type===
Depending on the quality of the result produced, assays may be classified into:
# '''Qualitative assays''', i.e. assays which generally give just a pass or fail, or positive or negative or some such sort of only small number of qualitative gradation rather than an exact quantity.
#'''Semi-quantitative assays''', i.e. assays that give the read-out in an approximate fashion rather than an exact number for the quantity of the substance. Generally they have a few more gradations than just two outcomes, positive or negative, e.g. scoring on a scale of 1+ to 4+ as used for blood grouping tests based on RBC [[Agglutination (biology)|agglutination]] in response to grouping reagents (antibody against blood group antigens).
# '''Quantitative assays''', i.e. assays that give accurate and exact numeric quantitative measure of the amount of a substance in a sample. An example of such an assay used in coagulation testing laboratories for the most common inherited bleeding disease - [[Von Willebrand disease]] is [[Von Willebrand Factor|VWF]] antigen assay where the amount of VWF present in a blood sample is measured by an immunoassay.
# '''Functional assays''', i.e. an assay that tries to quantify functioning of an active substance rather than just its quantity. The functional counterpart of the VWF antigen assay is [[Ristocetin]] Cofactor assay, which measures the functional activity of the VWF present in a patient's plasma by adding exogenous [[Formaldehyde#Tissue fixative and embalming agent|formalin-fixed]] [[platelet]]s and gradually increasing quantities of drug named ristocetin while measuring agglutination of the fixed platelets. A similar assay but used for a different purpose is called [[Ristocetin Induced Platelet Aggregation]] or RIPA, which tests response of endogenous live platelets from a patient in response to Ristocetin (exogenous) & VWF (usually endogenous).

===Sample type and method===
Depending on the general substrate on which the assay principle is applied:
#'''Bioassay''': when the response is biological activity of live objects. Examples include
##''in vivo'', whole organism (e.g. mouse or other subject injected with a drug)
##''ex vivo'' body part (e.g. leg of a frog)
##''ex vivo'' organ (e.g. heart of a dog)
##''ex vivo'' part of an organ (e.g. a segment of an intestine).
##tissue (e.g. limulus lysate)
##cell (e.g. platelets)
#'''[[Ligand binding assay]]''' when a ligand (usually a small molecule) binds a receptor (usually a large protein).
#'''[[Immunoassay]]''' when the response is an antigen antibody binding type reaction.

===Signal amplification===
Depending on the nature of the signal amplification system assays may be of numerous types, to name a few:
#'''[[Enzyme assay]]''': Enzymes may be tested by their highly repeating activity on a large number of substrates when loss of a substrate or the making of a product may have a measurable attribute like color or [[absorbance]] at a particular wavelength or light or [[Electrochemiluminescence]] or electrical/redox activity.
#Light detection systems that may use amplification e.g. by a [[photodiode]] or a [[photomultiplier tube]] or a cooled [[charge-coupled device]].
#'''[[Radioisotope]]''' labeled substrates as used in [[radioimmunoassay]]s and equilibrium dialysis assays and can be detected by the amplification in [[Gamma counter]]s or [[X-ray plate]]s, or [[Photostimulated luminescence|phosphorimager]]
#'''[[Polymerase Chain Reaction]]''' Assays that amplify a DNA (or RNA) target rather than the signal
#'''Combination Methods''' Assays may utilize a combination of the above and other amplification methods to improve sensitivity. e.g. [[ELISA|Enzyme-linked immunoassay]] or EIA, [[enzyme linked immunosorbent assay]].

===Detection method or technology===
Depending on the nature of the Detection system assays can be based on:
#'''Colony forming''' or [[virtual colony count]]: e.g. by multiplying bacteria or proliferating cells.
#'''[[Photometry (optics)|Photometry]]''' / '''[[spectrophotometry]]''' When the absorbance of a specific wavelength of light while passing through a fixed path-length through a cuvette of liquid test sample is measured and the absorbance is compared with a blank and standards with graded amounts of the target compound. If the emitted light is of a specific visible wavelength it may be called '''[[colorimetry]]''', or it may involve specific wavelength of light e.g. by use of [[laser]] and emission of [[fluorescent]] signals of another specific wavelength which is detected via very specific wavelength optical filters.
#'''[[Transmittance]]''' of light may be used to measure e.g. clearing of opacity of a liquid created by suspended particles due to decrease in number of clumps during a platelet [[Agglutination (biology)|agglutination]] reaction.
#'''[[Turbidimetry]]''' when the opacity of straight-transmitted light passing through a liquid sample is measured by detectors placed straight across the light source.
#'''[[Nephelometry]]''' where a measurement of the amount of light scattering that occurs when a beam of light is passed through the solution is used to determine size and/or concentration and/or size distribution of particles in the sample.<ref>{{cite web |url= http://medical-dictionary.thefreedictionary.com/nephelometry|title=Nephelometry |date=2016 |website=The Free Dictionary |publisher=Farlex |access-date=9 September 2016 }}</ref>
#'''[[Reflectometry]]''' When color of light reflected from a (usually dry) sample or reactant is assessed e.g. the automated readings of the strip urine dipstick assays.
#Viscoelastic measurements e.g. viscometry, elastography (e.g. [[thromboelastography]])
#Counting assays: e.g. optic [[Flow cytometry|Flow cytometric]] cell or particle counters, or [[Coulter principle|coulter]]/impedance principle based cell counters
#Imaging assays, that involve image analysis manually or by software:
##'''[[Cytometry]]''': When the size statistics of cells is assessed by an image processor.
#Electric detection e.g. involving [[amperometry]], [[Voltammetry]], [[coulometry]] may be used directly or indirectly for many types of quantitative measurements.
#Other physical property based assays may use
##[[Osmometer]]
##[[Viscometer]]
##[[Ion Selective electrode]]s
##[[Syndromic testing]]