Interpretive Handbook

Test 8668 :
X and Y Aneuploidy Detection, Buccal Smear, FISH

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Aneuploidy of the sex chromosomes is common among recognized congenital syndromes. For example, the majority (80%) of individuals with Klinefelter syndrome have 2 X chromosomes and 1 Y chromosome; the remainder are mosaics or variants. Individuals with Turner syndrome have a single X chromosome in 55% of cases; the remaining 45% are either variants or mosaics.

Useful For Suggests clinical disorders or settings where the test may be helpful

As a supplement to conventional cytogenetic analysis in patients with normal or uncertain cytogenetic results for sex chromosome aneuploidy or when an alternative tissue needs to be studied


To screen individuals suspected of having sex chromosome aneuploidy


As a means to rapidly determine the sex chromosome complement

Interpretation Provides information to assist in interpretation of the test results

Specimens that contain >5% cells with a signal pattern other than XX in females and XY in males have a very high likelihood of having a clone of cells with an abnormal complement of sex chromosomes.


Specimens with <5% of cells with a signal pattern other than XX in females and XY in males most likely do not have a clone of cells with an abnormal complement of sex chromosomes, but the presence of an abnormal clone of cells is not completely ruled out.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Conventional cytogenetic analysis should be performed for confirmation, especially when the results are abnormal.


Structural abnormalities of X and Y chromosomes will be missed by this technique, as will low-level mosaicism.


This test can detect between 50% to 70% of Turner syndrome cases (only those caused by complete lack of 1 sex chromosome [45,X] or high-level mosaicism for a 45,X). Congenital blood chromosome analysis (CMS / Chromosome Analysis, for Congenital Disorders, Blood) should always be performed for Turner syndrome.


The test does not rule out numeric or structural cytogenetic anomalies involving chromosomes other than X and Y.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

XX in females; XY in males

Clinical References Provides recommendations for further in-depth reading of a clinical nature

Babovic-Vuksanovic D, Michels VV, Law ME, et al: Guidelines for buccal smear collection in breast-fed infants. Am J Med Genet 1999;84:357-360