Rapid measurement of formed blood component sedimentation rate from small sample volumes
Devices and methods are described for measuring formed blood component sedimentation rate. Some of the methods may use (1) centrifugal techniques for separating red blood cells from plasma and (2) video and/or still imaging capability. Both may be used alone or in combination to accelerate formed blood component sedimentation and to measure its rate. In one example, the method may advantageously enable rapid measurement of sedimentation rate using small blood sample volumes. Automated image analysis can be used to determine both sedimentation rate and hematocrit. Automated techniques may be used to compensate for effects of hematocrit on uncorrected sedimentation rate data.
1. A system for processing a blood sample, the system comprising:
a centrifuge;
a sample vessel holder on the centrifuge for mounting a sample vessel;
a image capture device for visualizing the blood sample in the sample vessel held by the sample vessel holder;
a processor programmed for:
using the image capture device to capture at least a first image of formed blood component and plasma interface positions in the blood sample at an initial time in a sample vessel;
accelerating blood component separation by centrifugation of the sample vessel;
using the image capture device to capture at least a second image of formed blood component and plasma interface positions at a second time after the initial time;
determining a sedimentation rate of the formed blood component based on at least the following: a time-related compaction curve and a hematocrit correction factor, wherein the time-related compaction curve for at least one formed blood component in said blood sample is determined after accelerated blood component separation has begun.
2. The system of claim 1 wherein the processor is programmed such that the second image is captured after accelerated blood component separation.
3. The system of claim 1 wherein the processor is programmed such that the second image is captured after at least one phase of accelerated blood component separation.
4. The system of claim 1 wherein the processor is programmed such that the second image is captured during a linear phase of accelerated blood component separation.
5. The system of claim 1 wherein the processor is programmed such that the second image is captured while the sample vessel is being rotated by the centrifuge.
6. The system of claim 1 wherein the processor is programmed such that the second image is captured when the centrifuge is stopped.
7. A method for processing a blood sample, the method comprising:
capturing at least a first image of formed blood component and plasma interface positions in the blood sample at an initial time;
using centrifugation on a blood sample for a period of time to separate formed blood components from plasma;
capturing at least a second image of formed blood component and plasma interface positions at a second time during accelerated blood component separation;
determining a sedimentation rate of the formed blood component based on at least the following: a time-related compaction curve and a hematocrit correction factor, wherein the time-related compaction curve for at least one formed blood component in said blood sample is determined after accelerated blood component separation has begun.
8. The method of claim 7 further comprising calibrating sedimentation rates from centrifuge based technique with sedimentation rates from a reference technique.
9. The method of claim 7 , wherein said blood sample is about 25 uL or less.
10. The method of claim 7 , wherein centrifugation occurs at a first speed for a first period of time and then at a second, faster speed for a second period of time.
11. The method of claim 7 , wherein centrifuging comprises using a centrifuge configured to allow the blood sample to be visually observed during centrifugation to establish interface positions of one or more formed blood components in the blood sample.
12. The method of claim 7 , wherein centrifuging comprises using a centrifuge having a window thereon to enable visual observation of the blood sample to establish erythrocyte/plasma interface positions over time.
13. The method of claim 7 , wherein centrifuging comprises using a centrifuge, a light source, and an image capture device to enable visual observation of the blood sample to establish formed blood component/plasma interface positions over time.
14. The method of claim 7 , wherein sedimentation rate is calculated based on position of a meniscus of supernatant liquid and an interface position of one or more formed blood components in the second image.
15. The method of claim 7 , wherein compaction curve data is collected by capturing a plurality of images of interface positions of one or more formed blood components in a centrifuge vessel over the time period.
16. The method of claim 15 , wherein pixel positions in the plurality of images are used to accurately determine interface position.
17. The method of claim 15 , wherein compaction curve data is collected while the sample is being centrifuged.
18. The method of claim 17 , wherein correcting for hematocrit comprises calculating a mathematical function for a plurality of formed blood component interface positions occurring in said curve, said function being operative to correct for sedimentation rate variations due to hematocrit.
19. The method of claim 17 , further comprising image transformation for conversion of a curved interface to a flat interface.