WEEK NUMBER EIGHTEEN

Hello everyone! A few weeks more and we're all back at school. This will be my last post for our SIP so, here it goes...


Before a person is allowed to donate blood, he or she has to undergo certain physical examinations. The donor centre representative evaluates the prospective donor with regard to general appearance, weight, temperature, pulse, blood pressure, pulse, blood pressure, haemoglobin, and presence of skin lesions.

In this post, I will be talking about donor haemoglobin testing.

One of the methods used at the blood bank to estimate the level of haemoglobin in a donor is by the copper sulphate method.

Principle

i. The method of haemoglobin estimation using copper sulphate method is based on the principle of specific gravity. If a drop of blood is dropped into copper sulphate solution, it becomes encased in a sac of copper proteinate which will prevent the specific gravity from changing for at least 15 seconds. If the specific gravity of the blood is higher than that of the solution, the drop will sink within 15 seconds. If not, the drop will hesitate, remain suspended, or rise to the top of the solution.

ii. A specific gravity of 1.053 corresponds to a haemoglobin concentration of approximately 12.5g/dL

iii. False positive results are rare and donors whose drop of blood sinks nearly always have an acceptable haemoglobin level. However, false negative reactions occur fairly commonly and can cause inappropriate deferral unless the haemoglobin level is checked using another method.


Specimen
Sample of blood obtained by finger prick.


Materials
i. Copper Sulphate Solution (specific gravity: 1.053)
ii. Glass beaker
iii. Cotton swabs, with 70% alcohol or spirit
iv. Sterile disposable lancets
v. Capillary tube
vi. Biohazard sharps box
vii. Disposable gloves
viii. Alcohol swab (individual pack)


Procedures

i. Make sure that the glass beaker (250ml) is clean and free of debris. Fill the beaker with copper sulphate solution until it is slightly above 200ml marking.

ii. Put on a pair of gloves.

iii. The donor’s middle or ring finger is normally chosen for the finger prick procedure. Avoid fingers with rings on. Clean the chosen finger using a piece of alcohol swab. Allow the alcohol to dry or wipe dry with a new piece of dry cotton swab. Discard the swabs in the biohazard waste bin. Do not re-use the swab.

iv. Prepare a disposable sterile lancet by pressing and turning the knob into the lancet until there is a ‘click’ sound.

v. Use your thumb to slightly press the donor’s finger from the top of the knuckle towards the tip. Puncture the finger firmly, near the end but slightly to the side, with the sterile disposable lancet. Ensure that there is a good free flow of blood. DO NOT SQUEEZE the puncture site repeatedly as this will dilute the drop of blood with excess tissue fluid and lower the specific gravity. Dispose off the lancet in the sharps box.

vi. Wipe away the first drop of blood from the punctured site with a new piece of cotton swab. Collect the second drop of blood in a capillary tube until it is at least three quarters full, without allowing air to enter the tube.

vii. Hold the capillary tube about 1cm above the surface of the copper sulphate solution in the glass beaker, and let one drop of blood fall gently by unassisted gravity from the tube into the solution. Dispose off the capillary tube in the sharps box. DO NOT FLICK the drop of blood out of the tube as this will lead to in accurate haemoglobin measurement.

viii. Observe the drop for 15seconds. If the blood drop has a higher specific gravity than the copper sulphate solution, it will sink within 15 seconds. If not, the sinking drop will hesitate, remain suspended or rise to the top of the solution.

ix. Discard the copper sulphate solution after every 20 tests or every 2-3 hour intervals or when the solution is turbid. If there is any floating blood residue on the surface, it should be removed with an applicator stick.


Interpretation

i. If the drop of blood sinks within 15 seconds, the haemoglobin is greater than 12.5g/dL which is acceptable for blood donation unless there are other conditions which require a higher pre-donation haemoglobin level.

ii. If the drop of blood does not sink or sinks very slowly, the haemoglobin is most likely less than 12.5g/dL, and the result must be rechecked using quantative haemoglobin estimation by the HemoCue haemoglobin test.

iii. Because the copper sulphate method is not a quantitative test, the quantitative method by the HemoCue haemoglobin test is necessary to check the exact level in donors who fail the test as it suggests that the haemoglobin is low and the donor may need medical advice


Limitations

i. This is not a quantitative test and it shows only whether the potential donor’s haemoglobin is below or above 12.5g/dL

ii. The copper sulphate solution must be stored in tightly capped containers to prevent evaporation. The solution should be kept at room temperature to brought to room temperature before it is used.


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