Table 3.

Case finding for coeliac disease in general practice of 6000 adults

Target diagnostic group	Prevalence (%)	Target No for screening	Estimate of No actually screened	Screen efficiency (% of target No)	Study % new coeliac diagnoses in screened patients	Previous diagnoses + likely No of new cases
Irritable bowel syndrome	1214	720	55	7.6	0/132 (apply 0.5/133)	2 + 2.7
“Tired all the time” (fatigue)	7.515 16	450	137	30.5	6/329	0 + 8.2
Anaemia diagnosed 1996-7 (study period)	3.3*	56	5†	8.9	15/126	0 + 6.7
Anaemia diagnosed before Oct 1996	?	118‡	36†	30.5‡	15/126	1 + 14
Total		1344	233	17.3		3 + 31.6

The example of irritable bowel syndrome shows how to use this table. The literature gives a prevalence of 11-14%¹⁴; we have taken 12% for our calculation. The target number for screening in a practice with 6000 adult patients is therefore 720. Using the contribution of this practice to the study population (41.7% of participants), the number estimated to have been screened is 55 (41.7% of 132), giving a screening efficiency of 7.6% (55/ 720). The percentage of patients screened in the study who were diagnosed as having coeliac disease was applied to the target number (as no patient was diagnosed as having coeliac disease, an adjusted prevalence of 0.5/133 was applied to 720); this yields a likely 2.7 new cases of coeliac disease in target patients with the irritable bowel syndrome, which is added to the pre-existing 2 cases. 

^*197 diagnoses of anaemia after full blood counts; 56 of these not explained by case notes. ^†Actually screened. ^‡Estimated.