There must be millions of stored blood samples in the US. In the case below the manufacturer only supplied calibration down to 0.1 whether that was the limit in 2004 or if it was a cheaper machine I don't know. The machine does the calculations.
Here's an extract from a Lab Procedure dated 2004 along with the link to the full manual:
The instrument automatically calculates all results. After testing is completed, results are printed and review by the technologist. Samples with results > 150 ng/mL are diluted off-line and repeated; results are corrected for the dilution factor. Samples with results < 0.1 ng/mL are repeated to confirm.
Results are reported to the nearest tenth (0.1). The lowest reportable PSA result is 0.1 ng/mL. The assay does not have a maximum reportable limit since off-line dilutions can be made to bring the concentration within the working range of the assay. Estimates of imprecision can be generated from long-term quality control pool results.
The upper reportable value is virtually unlimited. The upper limit for undiluted specimens is determined by the calibration material supplied by the manufacturer. Values exceeding this upper limit are repeated on dilution until values, prior to correction for dilution, fall between approximately 5.0–150.0 ng/mL B. The lowest reportable value is approximately 0.1 ng/mL. The lower limit of this assay’s default dilution is determined by the calibration material supplied by the manufacturer. Values below this lower limit are repeated to confirm the result.
The residual serum is stored at ≤ –70o C for 6 months after analysis, then it is returned to the NHANES Repository in Rockville, MD for long-term storage.