Methods and devices for diagnosis of particles in biological fluids
Methods for determining whether certain compounds, in particular crystals, are present in a sample of a biological fluid that indicates an individual has a particular disease or condition, such as but not limited to gout, pseudogout or urinary tract stones. In some embodiments, the methods include the steps of digestion and filtration of a sample of synovial fluid in order to isolate, if present, monosodium urate monohydrate (MSU), calcium pyrophosphate dihydrate (CPPD), or calcium phosphate crystals from the sample, wherein the filtrate is analyzed with a Raman device to ascertain the presence and type of the crystals. Devices for performing steps of the method are disclosed.
1. A filter cartridge for collecting crystals from a fluid, comprising:
a) a filter holder having a base including an outlet and a top including an inlet;
b) a condensing piece located within the filter holder and having an inlet and an outlet, with the outlet in fluid communication with the filter base;
c) a filter membrane located between the condensing piece and the filter holder top, wherein the condensing piece channels flow of a fluid through the filter membrane such that a filtrate is collected at a location on the filter membrane that is smaller than a total surface area of the filter membrane; and
d) an interference blocking disc located between the condensing piece and the filter membrane, wherein the disc includes an aperture that allows fluid to pass therethrough, and wherein the disc is a metal disc.
2. The filter cartridge according to claim 1 , wherein the disc comprises aluminum and wherein the condensing piece comprises an epoxy casting.
3. The filter cartridge according to claim 2 , wherein an o-ring is present in a fluid flow direction between the filter holder inlet and the filter membrane.
4. The filter cartridge according to claim 1 , wherein the filter cartridge is designed such that the filtrate is placed on the filter membrane at a spot having a diameter less than 2 mm.
5. The filter cartridge according to claim 4 , wherein the filter cartridge is designed such that the filtrate is placed on the filter membrane at a spot having a diameter less than 1 mm.
6. A method for determining if a particle or crystal is present in a sample of biological fluid, comprising the steps of:
a) obtaining a sample of a biological fluid;
b) filtering the biological fluid through the filter cartridge of claim 1 , to recover particles or crystals in the filter cartridge;
c) analyzing the crystals with a Raman spectroscopy device in a Raman system; and
d) determining if the particles or the crystals are present, wherein the Raman system includes a receptacle adapted to receive the filter cartridge containing the filtrate.
7. The method according to claim 6 , wherein the filter cartridge is placed in the receptacle such that the filtrate in the filter cartridge is located within 10 to 250 microns of a focal point of a laser of the Raman system.
8. The method according to claim 7 , wherein the receptacle is mounted on a translation stage, and wherein the translation stage is moved from a first position to at least a second position in order to acquire spectra at different locations of a sample in order to increase an area of the filtrate surveyed.
9. The method according to claim 8 , wherein a Raman spectrum acquired at each point is processed to remove fluorescence background and subtract any peaks related to the filtrate of the filter cartridge.
10. The method according to claim 6 , wherein the biological fluid is blood, urine or synovial fluid.