Week 7

Hi all, for the past 3 weeks, I was attached to the haematology lab. Like other clinical labs, it operates 24 hours and is very busy almost everyday. The most common test ordered is full blood count, but since sofie has already touched on it, I shall talk about other tests.

Before that, do you know how specimens reach the lab? All along I thought they were sent in by some medical staff every now and then. But one day when I was helping out at the reception, I realised it was not. The specimens are received in the lab via a pneumatic transport system (that looks like water pipes) that is linked from every single ward or clinic to the lab. Samples from the wards to be sent to the lab are placed into a capsule, which contains a micro-chip that is recognised by the system to direct its way to its destination. In every ward or clinic, there will be this cupboard that contains the ‘pipe’. Empty capsules with reports from the lab (if available) will then be sent back to the respective wards using the same system. But because there is only one lane for sending out, the destination code must be keyed to ensure that they are sent back to the correct place. Isn’t this interesting? The WHOLE hospital is connected by all these ‘pipes’.

Capsules arriving from wards

Capsules waiting to be sent back to clinics/wards

Sending back capsules with reports through the one and only lane
(destination code keyed)

Ok, back to haematology. ESR (Erythrocyte Sedimentation Rate) is one of the most common tests performed in the haematology lab. There are many ways to test for the ESR. In my lab, the sedi-rate P4-Micro System is used. It measures the rate at which red cells fall in the first 50 mins when anti-coagulated blood is allowed to stand. Red cell sedimentation occurs in 3 stages: in the preliminary stage where aggregates form within a few minutes. This is followed by a period of time in which the sinking of the aggregates takes place at a constant speed. Finally, as the aggregated cells pack together at the bottom of the test tube, sedimentation rate slows down.

ESR is used to help diagnose conditions associated with acute and chronic inflammation. When inflammation is present in the body, certain proteins cause red blood cells to stick together and fall more quickly than normal to the bottom of the tube. These proteins may be produced when there an infection, autoimmune disease, or cancer. However, ESR is said to be nonspecific because increases do not indicate the exact site of inflammation or the causative agent. For this reason, a sedimentation rate is done in conjunction with other tests to confirm a diagnosis. Once a diagnosis has been made, a sedimentation rate can be done to help check on the disease or see how well treatment is working.

To perform ESR:

1. 320µl of blood is transferred into an aquisel tube, which contains 0.08ml of sodium citrate.
2. Then, a thin pipette is being pushed downwards into the tube, until the blood fills the whole pipette, indicated by the ‘0’ marking.
3. Next, the tube with pipette will be allowed to stand.
4. Exactly after 50 mins, the number of mm the red cells fallen would be read.
5.Results are then recorded in the ESR record book and the request form, and entered manually into the LIS.

Source taken from: http://www.globescientific.com/sedirate™-autozero-westergren-esr-system-3469-pi-574.html

Another special test that I think relates to what we have learnt is the Kleihauer Betke Test (KB), which is used to detect the presence of foetal RBCs in the mother’s blood using the principle of acid elution (dissolving of cells). KB Test can be used to assess 3 conditions.

One of which is when a newborn baby is found to be anaemic. In this case, the test checks whether the baby’s blood had entered the maternal circulation. If positive, the amount of blood must be determined and from there, the doctor will be able to decide how much blood should be transfused.

The second condition is, when the mother is Rh(-ve) and baby is Rh(+). If the KB test reflects a positive result, rhogam must be administered within 72 hours to neutralize the foetal RBCs.

Also, KB test plays an important part in cytogenetic analysis. To detect genetic abnormalities such as down syndrome, blood from unborn foetus must be analysed. To facilitate the process, the foetus’s blood must be taken through the mother’s tummy. The KB test will confirm whether the taken blood belongs to that of the foetus and not the mother.

Foetal RBCs contain mainly HbF (a2g2). They resist acid elution more than that of adult RBCs, which contain mainly HbA (a2b2). With this principle, foetal cells can take up the eosin when counterstained and appear as darkly stained red cells. On the other hand, adult cells will be disintegrated by the acid and therefore will appear as ghost cells (because the cells are dissolved, there is no more cells present to take up the stain).

To perform the KB test:

1. 3 different smears (patient’s blood, blood of a male and cord blood) are first made. Cord blood smear act as the positive control, blood smear from male acts as the negative.

2. Slides are air dried.

3. Slides are fixed in 80% ethanol for 10 mins then stained using the acid elution method.

4. This is followed by counterstaining with eosin for 3 mins and then air dried.

5. Finally slides are examined under the microscope at high power.

The proportion of foetal RBCs that appear as pinkish red intact cells to that of adult RBCs (appear as ghost cells) is assessed in several fields. If foetal cells are detected, report the number of foetal cells seen in 2000 adult cells and the volume will be calculated.

Ka Hang

TG02