:Diascopy
{{Short description|Medical test of skin blanching}}
File:Diascopy of a red dot basal cell carcinoma on the left mid back of a 74-year-old female.jpg on the left mid back of a 74-year-old female. The red dot basal cell carcinoma on the left mid back is circled; the tumor blanches when a glass microscope slide is pressed against it. From a case series by Philip R Cohen, 2017.{{cite journal | vauthors = Cohen PR | title = Red Dot Basal Cell Carcinoma: Report of Cases and Review of This Unique Presentation of Basal Cell Carcinoma | journal = Cureus | volume = 9 | issue = 3 | pages = e1110 | date = March 2017 | pmid = 28465868 | pmc = 5408973 | doi = 10.7759/cureus.1110 | doi-access = free | url = }}]]
Diascopy is a test for blanchability performed by applying pressure with a finger or glass slide and observing color changes.Marks, James G; Miller, Jeffery (2006). Lookingbill and Marks' Principles of Dermatology (4th ed.). Elsevier Inc. Page 29. {{ISBN|1-4160-3185-5}}.{{Cite journal|url=https://pubmed.ncbi.nlm.nih.gov/13410135/|title=Investigative and clinical studies with diascopy in dermatology|first1=L.|last1=Goldman|first2=H.|last2=Plotnick|first3=I.|last3=Balinkin|date=May 9, 1957|journal=Archives of Dermatology|volume=75|issue=5|pages=699–705|via=PubMed|doi=10.1001/archderm.1957.01550170067012|pmid=13410135}}{{Cite journal|title=Clinical value of diascopy and other non-invasive techniques on differential diagnosis algorithms of oral pigmentations: A systematic review|first1=Pérez-López|last1=D|first2=Peña-Cristóbal|last2=M|first3=Otero-Rey|last3=EM|first4=Tomás|last4=I|first5=Blanco-Carrión|last5=A|date=October 1, 2016|journal=Journal of Clinical and Experimental Dentistry|volume=8 |issue=4 |pages=e448–e458 |doi=10.4317/jced.53005 |pmid=27703615|pmc=5045694 }}{{Cite journal|url=https://pubmed.ncbi.nlm.nih.gov/12004702/|title=Diascopy: a clinical technique for the diagnosis of vascular lesions|first1=M.|last1=Rudd|first2=R.|last2=Eversole|first3=W.|last3=Carpenter|date=March 9, 2001|journal=General Dentistry|volume=49|issue=2|pages=206–209|via=PubMed|pmid=12004702}}
It is used to determine whether a lesion is vascular (inflammatory or congenital), nonvascular (nevus), or hemorrhagic (petechia or purpura). Hemorrhagic lesions and nonvascular lesions do not blanch ("negative diascopy"); inflammatory lesions do ("positive diascopy"). Diascopy is sometimes used to identify sarcoid skin lesions, which, when tested, turn an apple jelly color.
Diascopy with glassware is used as a method of diagnosing bacterial meningitis, as the rashes caused by the illness are non-blanching.{{Cite web |title=Meningitis Glass Test - Meningitis Rash Test |url=https://www.meningitisnow.org/meningitis-explained/signs-and-symptoms/glass-test/ |access-date=2025-05-10 |website=Meningitis Now |language=en}}