Lens-free point-of-care system diagnoses spinal meningitis

Spinal meningitis is an acute inflammation of the membranes covering the brain and spinal cord, which can be fatal within 24 hours. Until now, early diagnosis of the infection required an operator using an optical microscope to manually count white blood cells in cerebrospinal fluid.

“Until now, this process has been operator dependent, which limits where it can be used and increases the likelihood of errors in counting blood cells,” said Sophie NhuAn Morel, a Co-author of the paper. “In our study, manual counts produced different results among five doctors.”

The bulky equipment and intensive human involvement, which can take 5-20 minutes to make a proper cell counting, make the traditional procedure unsuited for point-of-care diagnosis. As a result, meningitis cannot be diagnosed in emergencies or operating rooms, or during routine medical care in developing countries.

Reported in a paper titled Lens-free Microscopy of Cerebrospinal Fluid for the Laboratory Diagnosis of Meningitis, Leti’s lens-free, operator-free technology requires fewer than 10µl of cerebrospinal fluid to differentiate between white blood cells (leukocytes) and red blood cells (erythrocytes) in a point-of-care environment, using very small equipment.

“Leti’s lens-free technology can count leukocytes and erythrocytes almost in real-time and can be used in many different environments outside the lab,” Morel said.

The lens-free microscope was tested on 200 patients at Marseille Timone Hospital in France to detect or confirm spinal meningitis. A blind lens-free microscopic analysis of 116 cerebrospinal fluid specimens, including six cases of microbiologically confirmed infectious meningitis, yielded a 100% sensitivity and a 79% specificity. Adapted lens-free microscopy is thus emerging as an operator-independent technique for rapidly counting leukocytes and erythrocytes in cerebrospinal fluid. In particular, this technique is well suited to the rapid diagnosis of meningitis at point-of-care labs.

In the near future, the reconstruction of both the magnitude and phase images from the raw diffraction pattern will allow the classification and numeration of all the blood cells in less than two minutes.