LOINC contains two types of descriptions, one at the Part level and one at the term level. Descriptions are attached to parts when the information is specific to the Part, such as Component or Method, and they are attached to the term when the information applies to the term as a whole and not to any individual Part of the term.

For example, the Component Part Glucose is associated with a description for the carbohydrate glucose, while the following term description describes the Peritoneal Equilibration Test, which applies to the combination of Glucose, Overnight dwell and Peritoneal dialysis fluid:

79264-8  Glucose [Moles/volume] in Peritoneal dialysis fluid --overnight dwell

A Peritoneal Equilibration Test (PET) is used to assess transport properties of the peritoneal membrane in patients undergoing peritoneal dialysis. Patients arrive at the dialysis unit in the morning with their overnight dwell fluid still in the abdomen. The overnight fluid is completely drained and sampled for testing. In the classic PET, 2000 ml of a 2.27% glucose solution is instilled and peritoneal dialysis is begun. Ten ml samples are drawn at time 0, 2, and 4 hours to measure creatinine, urea, and glucose. The PET assesses the rate of solute equilibration between peritoneal capillary blood and dialysate based on the ratio of the solute concentrations in dialysate and plasma (D/P). PET results are used to adjust various aspects of a patient’s peritoneal dialysis regimen, including dwell time, number of exchanges, and dialysis volume and composition. [PubMed: 7474677]