Method of introducing a liquid into a measuring tube

The disclosure relates to a method of introducing a liquid into a measuring tube and to a device for use in the method. In the specific embodiment the method is used in determining the erythrocyte sedimentation rate of a blood sample. This involves the steps of providing a device comprising a transparent tube and a cap fitted in airtight fashion to a first end portion of the tube and having a skirt which makes airtight sealing engagement with the tube. The cap is slidable along the tube from a first position to a second position closer to the first end of the tube, while still maintaining airtight sealing engagement. A second end portion of the tube is immersed in a blood sample and the cap is slid along the tube towards its said second position to draw a column of blood into the tube. The tube is then removed from the sample and the device is maintained in an upright position for a predetermined length of time. At the end of that time, the extent to which erythrocytes in the blood have settled is determined and provides an indication of the erythrocyte sedimentation rate of the blood sample.

This invention relates generally to a method of introducing a liquid into a 
tube and to a device for use in the method. More particularly the 
invention has been devised in connection with a method of determining the 
erythrocyte sedimentation rate of a blood sample. 
In the diagnosis of blood disorders, the rate at which erythrocytes (red 
corpuscles) settle out of a blood sample is commonly used as a primary 
indicator of whether or not the sample is normal. The sample is placed in 
a calibrated measuring tube and allowed to stand for a predetermined 
length of time, after which note is taken of the extent to which the 
erythrocytes have settled out. In a blood sample containing, say, 
hepatitus virus, the erythrocytes will settle to a significantly greater 
extent than in the case of a normal blood sample. 
Techniques previously used for introducing a blood sample into a measuring 
tube have had significant shortcomings. For example, in one case, the 
blood is aspirated into the tube by mouth; however, this has the risk that 
the technician performing the technique is exposed to possible 
contamination by viruses and the like in the blood. Mechanical aspirator 
devices used to avoid this problem are often difficult to manipulate and 
do not allow blood to be raised in a steady and controlled fashion, with 
the result that spillage and contamination of blood samples often occurs. 
For example, U.S. Pat. No. 3,373,601 (Monn) discloses a device comprising a 
container for a blood sample and a calibrated tube which can be inserted 
into and slid axially of the container. The container has an annular lip 
which seals against the wall of the tube so that, when the tube is pushed 
into the container it acts in the manner of a piston, forcing the blood up 
into the tube. The problem with this device is that, unless extreme care 
is taken to slowly and carefully push the tube into the container, the 
tube will be displaced too quickly and the blood will rise rapidly in the 
tube and squirt out of its open upper end. This is not only highly 
inconvenient and unhygienic, but is also potentially dangerous since the 
blood sample may be contaminated. 
Broadly considered, an object of the present invention is to provide an 
improved method of introducing a liquid into a tube. A more particular 
object is to provide an improved method of determining the erythrocyte 
sedimentation rate of a blood sample. 
According to a first aspect of the invention, there is provided a method of 
introducing a liquid into a tube. The method involves a first step of 
providing a device comprising: an elongate transparent tube which is open 
at both ends and a cap fitted to a first end portion of the tube. The cap 
has a closed top and a skirt which depends from said top and which makes 
airtight sealing engagement with the tube. The cap is slidable along the 
tube from a first position to a second position closer to the first end of 
the tube than the first position while maintaining said airtight sealing 
engagement. The next steps are to arrange the cap at its said first 
position and immerse a second end portion of the tube in a liquid. While 
maintaining the second end of the tube immersed in the liquid, the cap is 
then slid along the tube towards its said second position to an extent 
sufficient to cause liquid to be drawn up the tube to the level of an 
appropriate one of the graduations. The tube is then removed from the 
liquid. The lumen of the tube is dimensioned so that the column of liquid 
is retained in the tube. 
According to another aspect of the invention, there is provided a method of 
determining the erythrocyte sedimentation rate of a blood sample. The 
method involves a first step of providing a device comprising: an elongate 
transparent tube which is open at both ends and a cap fitted to a first 
end portion of the tube. The cap has a closed top and a skirt which 
depends from said top and which makes airtight sealing engagement with the 
tube. The cap is slidable along the tube from a first position to a second 
position closer to the first end of the tube than the first position while 
maintaining said airtight sealing engagement. The next steps are to 
arrange the cap at its said first position and immerse a second end 
portion of the tube in the blood sample. While maintaining the second end 
of the tube immersed in the blood sample, the cap is then slid along the 
tube towards its said second position to an extent sufficient to cause 
blood to be drawn up the tube to an appropriate level. The tube is then 
removed from the blood sample and maintained in an upright position with 
the first end portion of the tube uppermost for a predetermined length of 
time. The lumen of the tube is dimensioned so that the column of blood is 
retained in the tube. After the predetermined length of time, the extent 
to which erythrocytes in the blood have settled is determined and provides 
an indication of the erythrocyte sedimentation rate of the blood sample. 
The invention also provides a device for use in performing the method.

Referring first to FIGS. 1 and 2, a device for use in determining the 
erythrocyte sedimentation rate of a blood sample is indicated generally by 
reference numeral 10. Device 10 includes an elongate transparent tube 12 
and a cap 14. Tube 12 is open at first and second ends 16 and 18 
respectively and is marked with a series of graduations which extend 
longitudinally of the tube 12 and which are generally denoted 20. In this 
embodiment the graduations are in millimeters and tube 12 is made of 
plastic. 
Cap 14 is a one-piece plastic moulding and is fitted in airtight fashion to 
the first end portion of the tube 12. The cap includes a closed top 21 and 
a depending generally cylindrical skirt 22 which makes airtight sealing 
engagement with the external surface of the tube 12. As can best be seen 
in FIG. 4, skirt 22 is formed with two internal sealing ribs 24 of annular 
form which engage the external surface of tube 12 and which actually 
provide the seal between the cap and the tube. Ribs 24 are generally 
wedge-shaped in cross-section and taper towards top 21 of the cap. The 
ribs permit cap 14 to be slid longitudinally along the tube 12 while 
maintaining said airtight sealing engagement. Cap 14 is slidable along the 
tube from a first position to a second position closer to the first end 16 
of tube 12. The cap is shown in typical first and second positions in 
FIGS. 1 and 2 respectively. 
When the device is to be used to determine the erythrocyte sedimentation 
rate of a blood sample, cap 14 is initially positioned at a suitable first 
position such as that shown in FIG. 1. The lower (second) end portion of 
the tube is then immersed in a blood sample as shown in that view. The 
sample is indicated at 26 and is contained in a laboratory flask denoted 
28. While the lower (second) end portion of the tube is maintained 
immersed in the blood sample, cap 14 is slid along tube 12 towards its 
upper (first) end. This causes a column of blood to be drawn up into tube 
12. Cap 14 is moved along tube 12 to an extent sufficient to draw the 
column of blood up to the level of an appropriate one of the graduations. 
In FIG. 2, the blood level is indicated at 30 and is at the level of the 
"0" graduation 20. However, it will be appreciated that any appropriate 
graduation may be selected. It will also be realized that the specific 
locations of the cap 14 in its said "first" and "second" positions are not 
critical. It is merely necessary that the extent to which the cap is moved 
be sufficient to draw a column of blood into tube 12 and up to the level 
of an appropriate one of the graduations. 
It will be seen from the drawings that the skirt 22 of cap 14 is outwardly 
flared in the region of its open end just below the ribs 24 as indicated 
at 22a, and terminates in a shoulder 32. This shoulder allows a person 
using the device to grasp the tube 20 between the fingers and palm of one 
hand and push the cap upwardly on the tube using the thumb of the same 
hand. This makes for convenient one-handed operation of the device. 
After the column of blood has been drawn into the tube 12 of the device as 
described, the tube is removed from the blood sample and the device is 
maintained in an upright position with its first end 16 uppermost, for a 
predetermined length of time. It will of course be appreciated that the 
lumen of the tube 12 is dimensioned to ensure that the blood is retained 
in and does not escape from the tube at this time. In FIG. 3, part of a 
suitable supporting rack for the device is shown at 34. It will be seen 
that the rack includes a series of openings through one of which the tube 
12 is inserted and which is dimensioned so that the device is supported by 
abutment of the shoulder 32 of cap 14 against the rack. 
After the expiry of a predetermined length of time, the extent to which 
erythrocytes in the blood in tube 12 have settled is determined by 
reference to the graduations 20. For example, in FIG. 3, the level of the 
erythrocytes is indicated at 36 and the level of the sample as a whole at 
38; the difference in levels is represented by clear blood plasma. Thus, 
in the present case, it will be seen that the erythrocyte level has 
dropped by 20 millimeters in the said predetermined length of time. On the 
basis of this figure, the erythrocyte sedimentation rate of the blood 
sample can be calculated and a determination made as to whether or not the 
sample is abnormal. 
In some cases, it may be desirable to dilute the blood sample using a 
sodium citrate solution before determining the sedimentation rate of the 
sample. The sodium citrate solution acts as an anti coagulent in the 
sample. Where this is to be done, the device provided by the invention may 
also be used to introduce the sodium citrate solution into the sample. 
Thus, by immersing the lower end of the tube of the device in a body of 
sodium citrate solution in a container and sliding the cap upwardly as 
described above, a predetermined volume of solution can be drawn into the 
tube and subsequently discharged into the blood sample by depressing the 
cap and thereby ejecting the blood sample from the lower end of the tube. 
It will of course be appreciated that the preceding description relates to 
a specific embodiment of the invention and that the invention is not 
limited to the particular form of the invention described with reference 
to the drawings. Thus, the invention may be used for introducing any 
appropriate liquids other than blood samples into measuring tubes and for 
transferring those liquids to other vessels as required. Examples of 
detail changes are that, although a plastic tube has been described, the 
tube could of course be made of glass. The graduations on the tube could 
be differently arranged and need not be numerically identified. Also, 
variations in the form of the cap are possible.