SeraCare Life Sciences Inc., which makes products for medical tests, said Tuesday that it agreed to acquire the medical test products unit of Serologicals Corp. for $3.7 million in cash, plus unspecified assumed liabilities.

SeraCare said it would take over the diagnostic manufacturing facilities and product lines subsidiary of Celliance, a Serologicals division. Celliance continues to own an idle production plant in Lawrence’s East Hills Business Park.

SeraCare said the purchase would allow it to increase its molecular diagnostic reagent, diagnostic intermediate and substrate product lines. Under the agreement, SeraCare gets a manufacturing plant in Milford, Mass., and will assume the lease on a manufacturing and distribution plant near West Bridgewater, Mass.

SeraCare said it expected the transaction to close in January.