Filtering blood
An independent blood filter device depends on flow geometry to deliver blood serum or plasma free of detrimental levels of hemoglobin. It depends critically on an upstream flow rate or pressure differential limiting control element or device that limits the rate of change of pressure differential across the filter element. Pre-evacuated versions can be used to simultaneously draw blood from a living being and provide pressure differential across the filter element between an evacuated collector and a supply end open to atmosphere. A unit pressurized by hand motion employs the external shape of a partially filled blood collection tube as a piston to produce pressure in advance of the control element or device to create the pressure differential across the filter element to a collector vented to atmosphere. The control element or device is disclosed in numerous forms, including specially sized flow constrictions and compliant arrangements.
1. A filtering device for filtering blood to obtain serum or plasma in a container, comparing:
a pre-evacuated container including inlet and outlet ends with access at both ends,
a filter located within the container, and
a flow rate limiting control element located upstream of the filter and designed to limit pressure differential across the filter, the flow rate control element including capillary restriction for limiting blood flow while still enabling continuous blood flow into said pre-evacuated container and after said capillary restriction blood flowing unimpeded within the container toward the filter substantially eliminating hemolysis associated with the filter.
2. The filtering device of claim 1 wherein the flow rate limiting control element is located outside the container.
3. The filtering device of claim 2 wherein the flow rate limiting control element is integral with a blood drawing needle assembly.
4. A filtering device for filtering blood to obtain serum or plasma in a container, comprising:
a pre-evacuated container including inlet and outlet ends with access at both ends,
a filter located within the container, and
a flow rate limiting control element located upstream of the filter and designed to limit pressure differential across the filter, the flow rate control element including capillary restriction for limiting blood flow and blood thereafter flowing unimpeded inside said container toward the filter, wherein the flow rate limiting element is constructed to provide for initial flow rate between 2 cc per minute and 10 cc per minute.
5. The filtering device of claim 4 wherein the flow rate limiting element is constructed to provide for the initial flow rate between 3 cc per minute and 6 cc per minute.
6. The filtering device of claim 1 or 4 wherein the limiting control element is located inside the container.
7. A filtering device for filtering blood to obtain serum or plasma in a container, comprising:
a pre-evacuated container including inlet and outlet ends with access at both ends,
a filter located within the container, and
a flow rate limiting control element located upstream of the filter and designed to limit pressure differential across the filter, the flow rate control element including capillary restriction for limiting blood flow toward the filter, wherein said capillary restriction of the flow rate limiting element includes a channel between about 0.5 inches and 4 inches in length, and includes an internal diameter between about 0.008 inches and 0.013 inches.
8. The filtering device of claim 7 wherein the flow rate limiting control element includes said channel 2 inches in length and said internal diameter of the order of 0.011 inches.
9. A filtering device for filtering blood to obtain serum or plasma in a container, comprising:
a pre-evacuated container including inlet and outlet ends with access at both ends,
a filter located within the container, and
a flow rate limiting control element located upstream of the filter and designed to limit pressure differential across the filter, the flow rate limiting control element including capillary restriction for limiting blood flow toward the filter and including a channel approximately 12 inches long.
10. A filtering device for filtering blood to obtain serum or plasma in a container, comprising:
a pre-evacuated container including inlet and outlet ends with access at both ends,
a filter located within the container, and
a flow rate limiting control element located upstream of the filter and designed to limit pressure differential across the filter, the flow rate control element including capillary restriction for limiting blood flow flowing toward the filter and passively limiting increase of the pressure differential across the filter when blood enters said pre-evacuated container in order to substantially eliminate hemolysis associated with the filter.
11. The filtering device of claim 1 , 4 , 7 , 9 or 10 wherein the material of the filter comprises glass microfibers and a micro-porous membrane on a locating support.
12. The filtering device of claim 1 , 4 , 7 , 9 or 10 wherein the container includes a tube.
13. The filtering device of claim 1 , 4 , 7 , 9 or 10 including an access septum at the inlet end of the container.
14. The filtering device of claim 13 including an access septum at the outlet end of the container.
15. The filtering device of claim 1 , 4 , 7 , 9 or 10 including, at the outlet end of the container, a removable element in the form of an end-plug including a serum or plasma holding cavity.
16. The filtering device of claim 15 constructed for drawing blood from a source.
17. The filtering device of claim 15 for drawing blood from a living being.
18. The filtering device of claim 1 constructed for controlling the incoming blood flow rate into the container such that the rate of increase of the pressure differential between the two sides of the filter stays below 30 mmHg per second when blood enters said pre-evacuated container.
19. The filtering device of claim 18 constructed to limit the rate of increase to stay below 20 mmHG per second.
20. The filtering device of claim 4 constructed for controlling the rate of increase of the pressure differential between the sides of the filter to stay below 30 mmHg per second when blood enters said pre-evacuated container.
21. The filtering device of claim 20 constructed to limit the rate of increase of the pressure differential to stay below 20 mmHg per second.
22. The filtering device of claim 10 constructed to define incoming blood flow rate into the volume at the inlet side of the filter to increase the pressure differential across the filter at a rate of increase below 30 mmHg per second when blood enters said pre-evacuated contaiter.
23. The filtering device of claim 22 constructed to limit the rate of increase of the pressure differential to stay below 20 mmHg per second.
24. The filtering device of claim 4 , 7 , 9 or 10 wherein the flow rate limiting control element is located outside of the container.
25. The filtering device of claim 4 , 7 , 9 or 10 wherein the flow rate limiting control element is integral with a blood drawing needle assembly.
26. The device of claim 1 , 4 , 7 , 9 or 10 constructed to produce a volume of between about 1 to 2 cc filtrate.
27. The device of claim 26 constructed to produce a volume of about 1.5 cc filtrate.
28. The filtering device of claim 1 wherein the flow rate limiting control element is constructed to proved said capillary restriction according to the Hagen-Poiseuille law for a designed capillary radius, capillary length and pressure drop.
29. The filtering device of claim 12 wherein the tube has a uniform inside diameter.
30. The filtering device of claim 13 wherein the access septum is pierced by a needle receiving said blood flow from the flow rate limiting control element.
31. The device of claim 7 , 9 or 10 wherein the flow rate limiting control element is located inside of the container.
32. The filtering device of claim 10 wherein the flow rate limiting control element is constructed to provide said capillary restriction according to the Hagen-Poiseuille law for a designed capillary radius, capillary length and pressure drop.