(Sharecast News) - Monoclonal antibodies developer and supplier Bioventix reported a 24% improvement in its normalised revenue in its half-year report on Friday, to £4.4m.The AIM-traded firm said normalised profit before tax was also 24% higher year-on-year at £3.2m for the six months ended 31 December, while its closing cash balance slipped to £5.5m from £5.6m a year earlier.Its board declared a 20% rise in the interim dividend to 30p per share."In comparing the revenues for the equivalent period in 2017, we have excluded a "one-off" back-royalty of £0.77m that featured in interims of the 2018 accounts to arrive at normalised figures," the Bioventix board explained.The company said vitamin D antibody sales continued at the "healthy levels" seen during the period second half of the 2018 financial year, with that contributing "significantly" towards its growth."Whilst this is very encouraging, there is increasing evidence of a plateau in the downstream global vitamin D assay market," Bioventix explained."Nevertheless, we have seen a growth in sales from some individual customers who appear to be performing well in the downstream market with our antibody."Diazyme have made progress with their vitamin D assay which has the attractive feature of being run on general 'chemistry' analysers."The firm said Boditech - another one of its customers which used the 'vitD3.5H10' antibody, had achieved "significant" success in the growing Asian vitamin D market with its vitamin D assay.Other revenue streams for the established antibodies to 'T3', 'NT-proBNP' and progesterone also performed well during the period, the board said.Sales relating to troponin antibodies were said to not have been significant in the context of the overall totals for the period."Nevertheless, we can see these revenues increasing and this provides encouragement for future sales performance."There is further evidence of a roll-out of high sensitivity troponin assays reported in the academic literature, though it is possible that some new use of such tests could be part of clinical evaluations or comparisons supported by supplies of free samples that would not register as commercial sales."Bioventix said its research activities continued in line with the plans it described in its 2018 annual report, with the company saying it would report further on those projects with its full-year results.The overall context of the business and the landscape in which it operated had not materially changed since the 2018 annual report, the board explained."We are delighted to be able to report such positive news for the current half-year."We are pleased with the continued success of our vitamin D antibody and the remainder of the core antibody business."We remain optimistic about our troponin revenues and the success of these high sensitivity troponin products around the world and we look forward to further progress in the second half of the year."