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 method comprising:
using an accelerated blood component separation technique on a blood sample in a non-capillary vessel for a first period of time at a first compaction force to separate formed blood components from plasma, wherein the first period of time occurs during an estimated linear portion of a compaction curve;
using image capture of the sample at two different times during the first period of time to determine an uncorrected sedimentation rate based on plasma/formed component interface location at those two different times;
using the accelerated blood component separation technique on the blood sample for a second period of time at a second, greater compaction force than the first compaction force; and
determining sedimentation rate of the formed blood component based on at least the following: the uncorrected sedimentation rate and a hematocrit correction factor based on the hematocrit of the sample;
wherein said determining occurs without determining a mathematical function for a non-linear segment of the sedimentation curve representative of the magnitude of intercellular erythrocyte repulsion in the blood sample.
2. The method of claim 1 wherein the accelerated blood component separation technique comprises centrifuging the blood sample.
3. The method of claim 2 , 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.
4. The method of claim 2 , wherein centrifugation uses 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.
5. The method of claim 2 , wherein centrifugation uses a centrifuge having a window thereon to enable visual observation of the blood sample to establish erythrocyte/plasma interface positions over time.
6. The method of claim 2 , wherein centrifugation uses 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.
7. The method of claim 2 , wherein compaction curve data is collected by capturing a plurality of images of interface positions of one or more formed blood components in the centrifuge vessel over the time period.
8. The method of claim 7 , wherein pixel positions in the plurality of images are used to accurately determine interface position.
9. The method of claim 7 , wherein capturing of images begins once the centrifuge has reached a minimum operating speed.
10. The method of claim 7 , wherein capturing of images begins when the centrifuge has begins rotation.
11. The method of claim 1 , wherein said blood sample is about 100 uL or less.
12. The method of claim 1 , wherein said blood sample is about 50 uL or less.
13. The method of claim 1 , 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.
14. The method of claim 2 , wherein compaction curve data is collected while the sample is being centrifuged.
15. The method of claim 2 , wherein centrifugation is used to obtain accurate values for the hematocrit and to correct for hematocrit impact on sedimentation rate measurement.
16. The method of claim 2 , further comprising image transformation for conversion of a curved liquid interface to a flat interface.
17. The method of claim 2 , further comprising using a processor programmed to record interface position during a least a portion of centrifugation.