The determination of serum prolactin by radioimmunoassay

The iodination of hPRL with 125 I utilizing chloramine-T technique at temperature 4 degrees C gave 125 I-hPRL having immunoreactivity. 125 I-hPRL could be used as a labelled compound for determination of human prolactin by radioimmunoassay. The assay was performed using 125 I-hPRL 5,000 cpm/tube and anti-hPRL 1 : 400,000 dilution (final) incubated at 25 degrees C for 24 hr. One percent dextran-coated charcoal suspension (0.5 ml) was used for separation of free from bound form. The criteria of reliability of the method was evaluated in terms of accuracy, precision, specificity and sensitivity. Under the condition of the assay, the addition of known amount of hPRL (6-50 ng/ml) to charcoaled serum, the recovery of the added hPRL was found to be 97.3-120.8%. The within and between assay variation were evaluated from replicate measurements of the same samples in the same assay and in three different assays. The percentage coefficients of variation was found to be 7.7-15.8% and 13.1-24.0% for within and between assays respectively. Cross-reactivities of tested several protein hormones indicated that the anti-hPRL was very specific. The sensitivity was found to be 1.90 ng/ml. The method was applied to measure serum prolactin for one cycle of 4 volunteers Thai women having normal menstrual cycle. The mean ± S D of serum prolactin was found to be 15.9 ± 5.6, 21.2 ± 12.7 and 16.4 ± 6.2 ng/ml at follicular phase, mid-cycle and luteal phase respectively