SHARES in Omega Diagnostics have plunged by one fifth after it announced further delays to its long awaited portable HIV testing kit.

The company admitted "months" will be needed to work on the CD4 device after an issue was discovered which affects its reliability when it is stored at room temperature for more than five weeks.

The discrepancy leads to more false positives and Omega said it was now in the process of trying to find out which component causes the instability.

Edward Valente, research and development director, said: "We need to sit down round the table and come up with ideas for what potentially could be causing it. Then we need to set up as much in parallel as possible different swap ins and swap outs of components to localise where it is. The first task is to identify what is causing it and then we can address how we might solve that."

Shares in Omega fell by 20.22 per cent, down by 4.62p to 18.25p.

The CD4 test for HIV provides a quick method of finding out if a person's white-blood-cell counts have fallen to levels where retroviral drug treatment is needed. It is expected to be of particular use in developing nations.

Asked about the timescale of solving the latest problem, which comes on the back of previous reliability issues, Mr Valente said it was not quantifiable but would likely be "a few months".

Once that issue is resolved the kit, which Omega has spent £1.1 million developing over the past three years, will still have to go for further field tests and gain regulatory approval before it would be ready for commercial deployment.

Omega's Alva headquarters has the facilities to produce 2.5 million of the tests in a single shift.

Interest in CD4 remains high with Omega stating it plans to initially introduce it in 13 sub-Saharan African countries working alongside large non-governmental organisations.

The disappointing CD4 update came as Omega announced a rise in profit for its most recent financial year while turnover increased four per cent from £11.6m to £12.1m.

Chief executive Andrew Shepherd said: "We are seeing increased profitability and strong cash position in the core business."

Pre-tax profits rose 26 per cent from £543,041 to £684,258 in the 12 months to March 31 this year.

The food intolerance part of the business was once again the strong performer with revenue up 15 per cent from £5.18m to £5.95m on strong sales in Poland, France, Spain, China, Canada, Brazil and Indonesia.

Allergy and autoimmune revenue dipped from £3.97m to £3.61m as a result of ongoing issues in its core German market.

The infectious disease arm recorded four per cent growth to £2.55m on more sales to an unnamed UK customer and growth in new export markets such as Nigeria.

Jag Grewal, sales and marketing director, said: "We are not seeing significant growth in infectious diseases. It is a highly competitive marketplace and very price sensitive."

On its allergy testing programme Omega said it now has 32 allergens that show equivalent performance to the market leading product.

Tests comparing the Allersys range to the market leading laboratory system are taking place in Italy and Spain at the moment.

Mr Valente added: "We have 32 allergens optimised, four or five bubbling under and a couple that we really want to get that are just causing difficulties. We are confident of getting close to the 40 which gives us the opportunity to put the commercialisation plans in place."

Finance director Kieron Harbinson confirmed the fit-out of the company's manufacturing facility in Pune India is around 90 per cent complete but there remains a number of bureaucratic hurdles to clear.

That site will initially act as a secondary manufacturing location for CD4.