Dry eye, though widespread, is under-diagnosed, in part because symptoms don’t always correlate with objective signs. Matrix metalloproteinase-9 (MMP-9), an inflammatory biomarker elevated in the tears of dry eye patients, may hasten early diagnosis when detected.

Knowing this, researchers explored the technique of the MMP-9 point-of-care test InflammaDry (Quidel). They found that the test had a different detection range depending on whether MMP-9 was preformed or active. The team analyzed each using the InflammaDry test at concentrations ranging from 50ng/mL to 1500ng/mL and three loading volumes (5mL, 10mL, 20mL). InflammaDry is said to detect MMP-9 levels of more than 40ng/mL.

They found that preform MMP-9 concentrations of 50ng/mL, 100ng/mL and 500ng/mL exhibited negative results for every loading volume. At 1000ng/mL, the 20mL volume was positive, whereas the 5mL and 10mL volumes were negative. At 1500ng/mL, all loading volumes were positive but the strength of the association depended on the loading volume (higher volume correlated more strongly). They also discovered that active MMP-9 concentration of 50ng/mL was negative for every loading volume. At 100ng/mL, they note that the 20mL and 40mL volumes showed positive results with similar positive band densities.

“Clinicians should be aware of the possibility of false negatives with low tear volumes despite elevated MMP-9 concentrations,” the study authors conclude.