Chromosome Analysis – Blood

Chromosome Analysis – Blood

Test Overview

CPT Code(s)

88230, 88262, 88280, 88291

Methodology

Culture / Microscopy / Karyotype

Specimen Requirements

Container: Sodium Heparin (green top tube)

Optimal Quantity: 4-5 ml

Minimum Quantity: 1-2 ml

Storage: Room Temperature

Stability at Room Temperature: 8 hours, then refrigerate

Transportation: Avoid freezing or heating over 35^OC

Turnaround Time

STAT, including infants 6 months or younger: Preliminary results in 24 hours

Routine: Final report in 7-10 days for 90% cases

Test Detail

Clinical Significance

A chromosome analysis on peripheral blood may be clinically significant to identify genetic conditions associated with indications such as, developmental delay, failure to thrive, congenital anomalies, dysmorphic features, intellectual disability, ambiguous genitalia, short stature, multiple miscarriages and infertility.  It may also be relevant in cases to confirm or exclude the diagnosis of known chromosomal syndromes.

Clinical Background

Chromosome analysis is the microscopic examination of chromosomes in the metaphase stage of the cell cycle.  This type of analysis detects changes of the chromosome modal number and within the chromosome structure. These changes include trisomies (i.e. 21 or Down syndrome), monosomies (i.e. 45,X or Turner syndrome), deletions (complete breakage of a chromosome segment resulting in partial monosomy) and balanced or unbalanced translocations (chromosomal material from 2 or more chromosomes that has completely broken off and reunited onto another chromosome causing partial monosomies/trisomies and resulting in congenital syndromes, miscarriages and infertility).

In some cases, the abnormalities only exist in a subset of cells, or mosaic background, and an increase in the number of metaphases examined is required to determine the percentage of cells representing the abnormality.  Sometimes even the highest banding resolution cannot detect submicroscopic changes and a FISH study is required (i.e. DiGeorge, Prader-Willi and Angelman syndromes).  Chromosome analysis on peripheral blood serves as a diagnostic study for multiple relevant genetic abnormalities in one test, whereas molecular studies are significant in cases where a diagnosis has been made or a suspicion exists and specific testing is targeted.

Methods

T-cells and B-cells from peripheral blood are stimulated using mitogens such as PHA and Lectin.  Short term cultures are harvested at 24 and 72 hours for STAT cases and at 48 and 72 hours for routine cases, then G-banded.

Analysis and karyotyping is carried out by two certified technologists at high resolution from 550 or above band level, reviewed by the manager and reported by the director.

Interpretation of Results

The morphologic interpretation and correlation of results on all cases is performed by a board-certified doctoral level scientist (laboratory director). The final report identifies the chromosomal sex and modal chromosome number.  If abnormalities are present, they are explained in a paragraph which helps to clarify and correlate chromosomal findings with phenotype. Genetic counseling is recommended when chromosome aberrations, mosaic conditions, or unusual results are found, along with recommendation for further testing (i.e. microarray).  References are included in the report to help the referring physician with interpretation, which include books or journals that contain appropriate information.