[Question #11257] Rapid Molecular Diagnostic System With RHAM

15 months ago

Dear Doctors,

Today I found the laboratory that I go to regularly was offering a new test for chlamydia and gonorrhoea. It said Rapid Molecular Diagnostic System with RNase Hybridization Assisted Amplification Method. They used a urine sample for it.

Limits of detection are 500 Copies/ml for chlamydia and 2000 Copies/ml for gonorrhoea.

On the result sheet it said: "Screening by LAMP assay" (is that the same thing?)

I would like to know how reliable the results of this method are. ChatGPT told me: "For specific STDs such as chlamydia and gonorrhoea, molecular tests like these have shown particularly high levels of accuracy. They can detect even low levels of bacterial RNA or DNA, making them effective for early detection of infections." 1. Is that accurate?

2. How does this method measure up against urine-based PCR tests?

3. How reliable is this for women using a urine sample (not a swap)

Thank you :)

H. Hunter Handsfield, MD

15 months ago

Welcome back. But sorry to report I can't answer these questions in the detail you might like. I was unaware of either RHAM or LAMP technology or test performance. To my knowledge, they are not yet approved or widely used in the US; from online searching, I believe they were developed in China. They both appear to be variations on the general lab methodology of nucleic acid amplification testing (NAAT), and in general NAAT tests are highly accurate for the various bacteria and viruses for which they are used. As a generalization, they are extremely sensitive, that is all infected specimens test positive. The main limitation can be that they detect DNA or RNA of a pathogen when viable virus or bacteria is absent -- having been cured, eradicated by the immune system, etc. In that sense, some positive results may be false. However, in general this isn't a serious problem; of course a positive result always needs treatment (better safe than sorry!).

1. For those reasons, I are the summary statement you quote probably is accurate, but I have no way to know for certain.

2. I cannot judge the accuracy compared to other NAATs, including PCR. On quick look at the medical literature, I see no reports comparing LAMP or RHAM with other NAAT methods in diagnosis of any STI.

3. All NAATs tested so far are very reliable on urine specimens. I expect these methods would be similar.

HHH, MD

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15 months ago

Thank you Dr. Handsfield. That helps a lot. I will just assume these tests are pretty much equivalent.