UK NEQAS IN CLINICAL CYTOGENETICS, 2003/4

Slide Assessment Scoring Guide

The TOTAL SCORE is a numerical estimate of slide quality calculated on a scale of 0-8 from G BANDING QUALITY. All types of specimen are scored using the same criteria.

1. G BANDING QUALITY

Score as follows:

i.	No banding 0 points	Includes attempted but very poor banding such that unequivocal chromosome pairing is not possible
ii.	Poor 2 points	About 150 bands per haploid set. Fine detail not visible but each chromosome can be unequivocally identified from landmark bands.
iii.	Moderate 4 points	About ISCN 400 bphs. Examples of this level of banding are: two distinct dark bands on each of 8p and 9p, and three distinct dark bands in the middle of 5q (5q14, 5q21, 5q23).
iv.	Good 6 points	About ISCN 550 bphs. You should be able to see four distinct dark bands on 18q, and three on 11p. 7q33 and 7q35 resolve and 22q13.2 will be visible
v.	Excellent 8 points	About ISCN 850 bphs. 6q16 should split; 6q24, 6q25.2 and 6q26 appear as three distinct dark bands; 11p14.1 resolves from 11p14.3; 15q12 is distinct; 20p has at least two dark bands.

Odd number scores for banding quality may also be used, i.e. a given metaphase can score better than one of the even number categories but be poorer than the next higher even number category. All integer banding scores between 0 and 8 are therefore available.

The ringed metaphases will be assessed for quality and a QA score will be assigned based on the mean score achieved rather than the best metaphase examined. Thus scores of 5,6,6 would be assigned as ‘6’ and 5,5,6 as ‘5’.

2. RECOMMENDED MINIMUM QUALITY

The recommended scores given below are defined as the lowest standard acceptable for a given reason for referral without issuing a qualified report.

	MINIMUM QUALITY G-Banding SCORE
Reason for referral
Routine prenatal diagnosis, e.g. for age or biochemical prescreens.	2
Aneuploidies and known large structural rearrangements.	2
Expected small structural rearrangements, including their prenatal diagnosis.	3
Possible small unknown structural anomaly, e.g. abnormal ultrasound scan, recurrent abortion, dysmorphic features, delayed development, mental retardation.	5
Microdeletion syndromes (where high resolution G-banding is considered applicable). FISH studies should be undertaken in appropriate cases	7

Relevant Citations

UKNEQAS (1999) Waters J.J., Waters K.S. Trends in cytogenetic prenatal diagnosis in the

UK: results from UKNEQAS external audit, 1987-1998. Prenat Diagn 19: 1023-1026

UKNEQAS (1998) External Quality assurance for Clinical Cytogenetics in the United Kingdom: Current status and future prospects. J Association of Genet Tech 24: 113-119

UKNEQAS (1994) Guidelines for Clinical Cytogenetics. ACC/UKNEQAS. Royal Institute of Public Health and Hygiene.