The Substance project is considering a change, which if implemented, will affect the mapping of LOINC terms.
The suggested change is to deprecate the instances of Free X (substance) and replace them with X (substance). E.g 259355006 | Free testosterone (substance) | will be deprecated and replaced by 43688007 | Testosterone (substance) |

The modelling of Testosterone has changed to reflect the change:

January 2018 release:

July 2018 release:

Currently the mapping of the LOINC Parts to SNOMED CT is as following (based on confirmation with RII). The changes in substance hierarchy will have an effect on mapping of the LOINC parts, specifically Testosterone and Testosterone total:

From LOINC website: Testosterone is an androgenic steroid and is the primary male sex hormone. Approximately half of circulating testosterone is tightly bound to a protein called sex hormone binding globulin (SHBG) and is biologically inactive. Another fraction is weakly bound to other proteins, such as albumin, and the remainder is unbound, or "free". Weakly bound and free testosterone together represent bioavailable testosterone. Both total and free testosterone levels decrease with age. Low testosterone is associated with many other conditions, including osteoporosis, Alzheimer’s disease, obesity, diabetes and ischemic heart disease.

Example LOINC terms:

 Other examples:

From LOINC website: "Bilirubin is an orange-yellow pigment produced by the normal breakdown of heme, a component of the hemoglobin found in red blood cells. It is processed by the liver and excreted in bile. Conditions that cause red blood cell breakdown or interfere with liver or bile processing can cause elevated levels of bilirubin. Bilirubin exists in many forms. Non-glucuronidated bilirubin (also called unconjugated or indirect) is the breakdown product of heme and is not water-soluble. Hemolytic anemias, which cause increased red blood cell breakdown, are one cause of elevated non-glucuronidated bilirubin. Glucuronidated bilirubin (also called conjugated) is a water-soluble form of bilirubin that is made in the liver by the addition of sugar molecules to non-glucuronidated bilirubin. Conditions that affect liver function (such as hepatitis, cirrhosis and liver tumors) or physically block the bile ducts (such as gallstones) can cause elevated levels of glucuronidated bilirubin. A third form of bilirubin is that which is bound to albumin, and it is also known as delta bilirubin because it was originally identified based on the unexpected difference between the total bilirubin level and the level of glucuronidated plus non-glucuronidated bilirubin in some patient samples. Prior to the discovery of albumin-bound bilirubin, the term "direct" bilirubin was used as a synonym for glucuronidated bilirubin, but direct bilirubin is actually glucuronidated PLUS albumin-bound bilirubin."