I am new to IVDs from a background in medical devices and am a little confused how meteorological traceability can work in IVDs when there are no reference measurement procedures for particular analyte in matrix concentrations and how to deal with assigned values which are not lengths and weights.
Let's assume hypothetically that we are an IVD manufacturer which produces an IVD kit for measuring NaCl in serum which requires an assigned value to a calibrator of 10 mg Sodium Chloride (NaCl) per 1 ml serum.
We are fortunate that there exists a reference standard material for Sodium Chloride (NIST Standard Reference Material 919b) with a described reference measurement procedure how this standard reference material was determined to have a known concentration of pure NaCl.
Let's assume further, that unfortunately there seems to be missing a reference measurement procedure for NaCl in serum and thus no reference measurement standard for NaCl in serum can be bought from any reference measurement laboratory or a measurement be ordered as a service. In this hypothetical world only the manufacturers IVD kit itself exists for which we want to create the calibrator.
What shall the IVD manufacturer do in this situation?
Is it allowed to maintain a meteorological traceability by weighting the analyte NaCl (for which we can buy traceable secondary standards) and weighting the matrix serum and manufacturing a calibrator of known concentration NaCl in serum by just mixing those two known quantities? We can verify the concentration then with the IVD kit, but it cannot measure with a higher order measurement procedure.
In other words does ISO 17511 allow any deviation from measurement of a concentration of analyte directly by arguing about how the lower level calibrator was produced by mixing analyte in matrix?
Let's assume hypothetically that we are an IVD manufacturer which produces an IVD kit for measuring NaCl in serum which requires an assigned value to a calibrator of 10 mg Sodium Chloride (NaCl) per 1 ml serum.
We are fortunate that there exists a reference standard material for Sodium Chloride (NIST Standard Reference Material 919b) with a described reference measurement procedure how this standard reference material was determined to have a known concentration of pure NaCl.
Let's assume further, that unfortunately there seems to be missing a reference measurement procedure for NaCl in serum and thus no reference measurement standard for NaCl in serum can be bought from any reference measurement laboratory or a measurement be ordered as a service. In this hypothetical world only the manufacturers IVD kit itself exists for which we want to create the calibrator.
What shall the IVD manufacturer do in this situation?
Is it allowed to maintain a meteorological traceability by weighting the analyte NaCl (for which we can buy traceable secondary standards) and weighting the matrix serum and manufacturing a calibrator of known concentration NaCl in serum by just mixing those two known quantities? We can verify the concentration then with the IVD kit, but it cannot measure with a higher order measurement procedure.
In other words does ISO 17511 allow any deviation from measurement of a concentration of analyte directly by arguing about how the lower level calibrator was produced by mixing analyte in matrix?