According to a preliminary analysis by the Clinton Health Access Initiative, the estimated need for the test is between 2.7 and 2.9 million people with a CD4 cutoff of 100, and 5.8 million with a CD4 cutoff of 200.

Abbott Laboratories, which makes the test, declined to say how many tests are sold, but one estimate pegs the figure at about 400,000 a year.

The low adoption numbers run the risk of discouraging companies interested in developing TB diagnostics, said Ms. Lessem.

“The W.H.O. is giving really mixed signals to countries and to suppliers and manufacturers, because they’re basically saying on the one hand we’re asking for this point-of-care test, we want to do more to stop mortality — and on the other hand, actually we think that even though we have this tool, it’s not worth rolling out,” Ms. Lessem said.

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Dr. Gilpin said W.H.O.’s guidance is so cautiously worded in part because of worries that the test would be misused for people with higher CD4 levels, in whom the test is less accurate.

This was a legitimate concern at one-time, Ms. Lessem said, but the pendulum has swung too far: “Now even people who need the test and would benefit from it are not getting it because the guidance is worded in such a restrictive way.”

Doctors Without Borders has compiled evidence that shows the test, called TB-LAM, is more sensitive than the 2015 data suggested. The W.H.O. planned to review that data this year, but now has decided to revisit TB-LAM along with a new urine dipstick, made by the Japanese company Fujifilm, in May 2019.