How do the units reported by the newborn screening laboratory compare to serum results?
• We will be reporting results in units of nmol/L blood and will not be doing an organic extraction step. If one assumes a 55% hematocrit, 1 nmol/L blood ~ 2.2 nmol/L serum. So a result on the screening assay of 50 nmol/L blood would be the equivalent to ~110 nmol/L serum. There are a number of other factors beyond hematocrit such as the affinity and specificity of the antibody used for the immunoassay, and sample preparation that might cause differences in results. • If you would like to get a better idea of how screening assay correlates with your diagnostic method, please feel free to have some blood spotted onto a filter paper card at the same time that the patient is having a serum 17OHP measured. We can then measure the blood dot 17OHP on these samples and let you know the result. Please remember that the screening assay is calibrated to perform better at higher concentrations as that is where the medical decision limit is for newborn screening. This means that the screening test
