An optical measurement instrument is an integrated instrument that includes an optical cavity with a light source, a sample cuvette, and an optical sensor. The instrument can be used for taking measurements of organism concentration in one or more samples. Preferably, the instrument holds multiple, individually-loaded, independent fluid samples and determines bacteria concentration via a forward-scattering signal. The instrument can incorporate onboard incubation to promote bacterial growth in the samples such that, once a certain bacterial concentration is achieved, the higher concentration sample can be used with a mass spectrometer to identify the type of bacteria. The instrument and mass spectrometer can be a part of a network for medical diagnostic testing data where data is stored in a manner that is inherently untainted by patient identifiable information.