Yield of abdominal ultrasound in patients with abdominal pain referred by general practitioners

Introduction

Patients with abdominal pain comprise 2–4% of all visits to general practitioners (GPs) [1–4]. Abdominal pain is one of the indications for performing abdominal ultrasound (US) [5]. In the Netherlands, GPs have open access to abdominal US. About 8% of patients with abdominal pain of unclear origin are referred by GPs for abdominal US [4], [6]. The purpose of this cross-sectional study was to examine the prevalence and determinants of significant abnormalities on abdominal US in patients with abdominal pain referred to the University Medical Centre Utrecht in the Netherlands by GPs.

Methods

This study was conducted with data from the computerized hospital database of the University Medical Centre Utrecht in the Netherlands from January to December 2002. All patients ≥ 18 y referred for abdominal US by GPs were extracted from the database, in which all data of the US referral forms filled in by GPs and US findings were available. In total, 499 patients were included with complaints of abdominal pain or a clinical suspicion of gallstones and/or renal stones. US for gynaecological indications is performed by gynaecologists, and excluded from this study.

A short questionnaire was sent to patients with an unclear abnormality detected with abdominal US in order to assess the consequences of the US finding. These findings were considered to be a significant abnormality when they resulted in referral to a specialist or hospital admission.

Multivariate logistic regression analysis was used to investigate whether gender, age, complaints of pain, other symptoms than pain, medical history and clinical suspicion of the GP were independent determinants of a significant abnormal finding on abdominal US.

Results

The mean age of the patients was 47.9 y (SD 15.2), and 150 patients (30%) were male. In total, 252 patients (51%) had complaints of localized pain, 149 patients (30%) general abdominal pain, and 50 patients (10%) colicky pain. In roughly half of the cases, clinical suspicions were mentioned; a clinical suspicion of gallstones in 125 patients (25%) and renal stones in 32 patients (6%).

Significant abnormalities were detected with abdominal US in 81 patients (16%), non-relevant abnormalities in 214 (43%), and no abnormality in 204 (41%). Significant abnormalities included 44 gallstones, 12 malignancies (four liver, three pancreas, two kidney, two bladder, one bowel), eight renal stones, six other abnormalities of the kidney, five gallbladder pathologies (three cystitis), two uterine myomatosis, one liver adenoma, one abdominal aortic aneurysm, one inguinal hernia, and one liver perforation.

Gallstones were often detected with abdominal US, in 72 patients (14%). Forty-four of these 72 gallstones (61%) were significant abnormalities and eventually resulted in laparoscopic cholecystectomy in 40 patients (56%).

Multivariate logistic regression analysis identified three relevant determinants of significant abnormal findings on abdominal US (Table I). Aging was associated with an increased risk of significant abnormality of 3% per year (95% CI 1.01–1.04). Colicky pain and a specific clinical suspicion of the presence of gallstones increased the risk of an abnormal finding by more than twofold, with 95% CIs of 1.04–7.66 and 1.26–4.40, respectively.

Table I.  The relation of baseline characteristics and indications with significant abnormality on abdominal ultrasound in 499 patients by multivariate logistic regression analysis.

	Significant abnormality, n (%)	Odds ratio	95% confidence interval
Gender
Female	52 (15)	Ref.	Ref.
Male	29 (19)	1.43	0.84–2.43
Age
Each year	–	1.03^a	1.01–1.04
Complaints of pain
General abdominal pain	36 (14)	1.18	0.45–3.08
Localized abdominal pain	22 (15)	1.19	0.48–2.97
Colicky pain	14 (28)	2.80^a	1.02–7.66
Other symptoms
Nausea/vomiting	7 (29)	2.09	0.80–5.45
Relevant medical history	15 (16)	1.13	0.59–2.15
Clinical suspicion of the GP
Gallstones	30 (24)	2.31^a	1.22–4.40
Renal stones	6 (19)	1.36	0.48–3.87
Other clinical suspicion	13 (14)	1.15	0.57–2.34

^a p ≤ 0.05.

Discussion

Four previous studies on abdominal US requested by GPs showed significant abnormalities in 25–30% of the abdominal US [7–10]. Only Charlesworth and Sampsom [8] presented percentages for relevant abnormalities in patients with left upper quadrant pain (n=27) and patients referred with lower abdominal pain (n=100): 18% for both patient groups. This percentage is comparable with the 16% significant abnormalities found in our study.

The present study showed three determinants of significant abnormal findings on abdominal US, i.e., age, colicky pain, and a clinical suspicion of gallstones. It is well known that morbidity increases with age. Our finding of a significant positive association of age with abnormal findings on abdominal US agrees with the study of Muris et al. [11], which also showed a positive association between age and organic disease in patients with abdominal pain. As expected, a significant association was found between colicky pain and significant abnormalities on abdominal US. A similar association was observed for a clinical suspicion of gallstones. The presence of a clinical suspicion of renal stones and other suspicions also showed a positive, but non-significant association.

This study has limitations. First, we used an existing data file for collection of information about indications and findings on abdominal US, which can lead to incomplete data. Secondly, the study was conducted in a university hospital, which can result in an overestimation of the prevalence of pathological findings.

Several questions are raised by the results of this cross-sectional study: What is the additional value of abdominal ultrasound in the 84% of the patients in whom no or non-relevant abnormalities were found, and do results of abdominal ultrasound change management decisions or have an effect on the outcome of illness? A prospective study in multiple general practices and hospitals is necessary to gain more insight into the additional value of abdominal ultrasound.