Patients receiving hemodialysis have the efficacy of dialysis determined by the result of the Kt/V. When the line that us used to dialyze the patient becomes compromised, the Kt/V decreases. One of the tools that nephrologists have to understand why the Kt/V is decreasing is to determine the percent recirculation, where some blood is recirculating before going through the dialyzer, essentially decreasing the efficiency of waste removal and the Kt/V result. The Arterial, Venous, and Peripheral BUN required for this calculation is included on the LOINC list, but the calculation itself is not, unless you are calling the test by another name. Is there a reason why the components of the test would be included on the list, but not the test/calculation name?