Paediatricians often order laboratory and radiological tests to identify children with potential rheumatological disease prior to subspeciality referral. However, the pattern of testing suggests inadequate understanding of their diagnostic utility and limitations. Herein we will address some of the most common rheumatological diagnoses encountered in the subspeciality clinic - juvenile idiopathic arthritis (JIA), juvenile spondyloarthritis (JSpA) and systemic lupus erythematosus (SLE), and related connective tissue diseases - and the tests most frequently ordered to diagnose them: anti-nuclear antibodies (ANA), rheumatoid factor (RF), human leukocyte antigen (HLA)-B27 and radiological tests. This article will highlight the sensitivity, specificity and positive predictive value of the tests. In general, none of these tests were appropriate to use as rheumatological 'screens', as no individual test was diagnostic. Specific tests should be ordered only when there is a high clinical index of suspicion for a particular disease entity. Greater understanding of a test's diagnostic utility should decrease unnecessary testing, anxiety and expense and aid in interpretation.