Add-on tests are tests that are performed on an existing specimen previously submitted to the pathology service with an earlier test order. The reasons for ordering an add-on test are many including situations when a clinician requires a base-line result in cases where treatment has already commenced, when the clinician neglected to order all prescribed tests, or even situations when a clinician wants to avoid subjecting vulnerable patients or children to additional phlebotomies. Add-on tests are labour-intensive and disruptive for the laboratory and place a disproportionate burden on laboratory resources.18 33-35 39 Interruptions to the routine work flow, interruption of clinical staff and delayed testing of the specimen are part of the impact of add-on testing. Measuring the number of add-on tests allows the laboratory to identify any major problem areas.33-35
Procedures to reliably identify add-on tests were not implemented until 2011 and, therefore, it was not possible to compare the add-on test rate for the period before electronic ordering became available. The results reported in Table 13 contrast add-on test rates for different hospitals and pathology departments. They show a variation between hospitals of between a minimum of 0.61% (Hospital B; specialist hospital) and maximum 2.24% (Hospital F; metropolitan general hospital). There were considerable differences in the rate at which add-on tests were ordered in the different departments. The departments with the highest proportion of add-ons were Serology, Immunology and Endocrinology (7.78% 7.22% and 6.33% respectively). The add-on test rates in the clinical chemistry and haematology departments, that combined accounted for 70% of the add-on test volume, were 2.56% and 0.69%, respectively.
| Proportion of Tests Accounted for by Add-on Tests (Number of Add-on Tests/Number of all Tests) | |||
| Hospital |  | Department | |
| | Andrology/Seminology | 0% (0/797) |
| | Bone Marrow | 0% (0/237) |
| | Clinical chemistry | 2.56% (8300/324178) |
| | Cytology | 0% (0/3095) |
| | Endocrinology | 6.33% (1358/21455) |
| | Genetics | 0.29% (7/2396) |
| | Haematology | 0.69% (1527/222374) |
| A | 2.04% (3654/178819) | Histopathology | 0.05% (1/1868) |
| B | 0.61% (189/31130) | Immunology | 7.22% (1199/16613) |
| C | 1.29% (632/49168) | Microbiology | 0.10% (98/97904) |
| D | 2.22% (1103/49615) | Non-gynae cytology | 0.65% (9/1381) |
| E | 1.92% (4569/238164) | Serology | 7.78% (1300/16700) |
| F | 2.24% (3796/169151) | Virology | 2.04% (144/7049) |
| Overall | 1.95% (13943/716047) | ||
Table 13. The proportion of pathology tests accounted for by add-on tests, the add-on test volume, and the total test volume, at each of the six study hospitals (first column) and each of the ten departments within the pathology service (third column) for the two-month period of August-September 2011.
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