The urine LAM Lateral Flow Assay is a test strip that may be used to pick of the Lipoarabinomannan in the urine of a TB infected patient. LAM (Lipoarabinomannan) is one of the components of the M. tuberculosis’ cell wall. There are some theories suggesting how does LAM reach the urine. It is said that the Mycobacterium is able to produce LAM at the site of infection, then this particle enters the blood stream, travels to the kidneys and then it is filtered into the urine. However, others furthers suggest that instead of renal filtration, a positive urine LAM may be due to renal involvement secondary to TB. We also know that a high incidence of patients with disseminated TB usually have renal TB (found at the time of biopsy, probably due to haematogenous spread). Therefore, we should keep in mind that urine LAM may be positive regardless of the severity of the respiratory symptoms since it actually indicates disseminated TB.

Urine LAM is best used in patients who have disseminated TB and are immunocompromised (HIV). Urine LAM concentrations increase according to the severity of immunosuppression. The lower the CD4+ count, the higher the urine LAM concentration in the urine. This means that if you test a patient who is HIV positive, but with a high CD4+ count then the urine LAM might come back negative. This is because the more “immunocompetent” individuals rarely develop haematogenous spread or disseminated TB.

A positive urine LAM test strip means that the patient has either disseminated TB or genito-urinary TB

Therefore urine LAM is most sensitive and it is most specific in patients with advanced immunodefienciecy. Urine LAM should not be used for patients who are HIV negative. WHO recommends that urine LAM be used in patients with a CD4 count < 200 (old guidelines used to say 200) OR for those who are seriously ill regardless of the CD4+ cell count. You should be discouraged to use the urine LAM without knowning the clinical assessment of the patient and without knowledge of the CD4+ count.  

This is a test where you use a micropipette to collect around 60 microliters (2 drops) of midstream urine and you test it with the detection kit test strip (like a pregnancy test/HIV Rapid test). It should be interpreted after 25-35mins. It is relatively affordable at around ?R70 per test. The results may be POSITIVE, NEGATIVE or INVALID.