Based on MULTI-AXIAL HIERARCHY (I believe), there are two “folders” at the highest level of LOINC: LOINCCLASSTYPES and LOINCPARTS. I always used LOINCPASRTS and ignored LOINCCLASSTYPES, but now I wonder… What is the difference between them? I came across a few codes that look like legitimate LOINC codes, but those concepts are not found in LOINCPASRTS and are instead in LOINCCLASSTYPES. How come? Let’s take, as an example, two codes: 48643-1 “Glomerular filtration rate/1.73 sq M.predicted.black:ArVRat:Pt:Ser/Plas:Qn:Creatinine-based formula (MDRD)” is under LOINCCLASSTYPES/Laboratory Class/Chemistry/ and 50381-3 “Creatinine renal clearance/1.73 sq M.predicted.male:ArVRat:Pt:Ser/Plas:Qn:Cockcroft-Gault formula, BSA formula” is under LOINCPARTS/Chemistry/Renal function/Creatinine/Creatinine | bld-ser-plas. Of course I realize these are different tests, but they are sufficiently similar for me to wonder why they are found in two completely different LOINC hierarchies? Why is 48643-1 not under LOINCPARTS somewhere? Thanks for your help!