Endocrine Abstracts

Although 24 h urinary 5-hydroxyindolacetic acid (5-HIAA) concentration is a well established test for the detection and monitoring of carcinoid tumours, compliance, adequacy of collection and the influence of dietary sources of serotonin are problems associated with this approach. Recently, a random urinary 5-hydroxyindolacetic acid creatinine ratio (R/5-HIAA/cr) test has become available which can be used in outpatient departments, however its correlation to 24 h 5-HIAA (24/5-HIAA) values remains uncertain.

We retrospectively analysed 1113 paired 24 h urinary 5-HIAA and spot urinary 5-HIAA/cr from 176 patients (mean age 61 (S.D. 12.99, 52% male) with carcinoid tumours diagnosed between 2005 and 2008.

The correlation between the two tests was examined using Pearson’s product moment correlation co-efficient (r). Overall a relatively strong correlation existed between the tests (r=0.79, P<0.0001). When the results were limited to the first paired sample from each patient (to remove the confounding effect of repeated measurements) the correlation for the overall sample (r=0.83, P<0.0001), for men (r=0.87, P<0.0001) and for women (r=0.81, P<0.0001) remained strong. Interestingly, the correlation between the tests was stronger for ages <55 (r=0.99, P<0.0001), 55–64 (r=0.92, P<0.0001) and >75 (r=0.93, P<0.0001). However, the 65–75 group had a reduced correlation (r=0.41, P<0.05). Whilst this studied highlights the poorer correlation in the 65–75 age range it is not clear why these results were observed.

In conclusion, we believe that there is a associated correlation between these two tests and that random urinary 5-HIAA/cr tests collected in the out-patients could be substituted for 24 h urinary 5-HIAA tests in carcinoid patients.