There are various stomach cancer blood tests that your doctor will want to do on you both prior to and after diagnosis.
They are used for screening and monitoring your condition as well as making sure that you remain healthy.
There are literally thousands of tests that can be done, but there are tests that are more specific to your condition.
The reason for writing this page for you is not to make you a master of diagnosis, rather to give you an idea of what your doctor is looking for and why.
Your sample is special to you, but one of many millions that are analysed worldwide each day.
Once taken, you need to have a better understanding of where your blood will be sent – you might be surprised it’s not one, but many laboratories that will test your samples.
The main laboratories your stomach cancer blood tests will be sent to are the haematology, chemistry and may be the immunology laboratories where they have various analysers that will churn out results.
When you spin blood it separates in to cells and plasma, the former will be of particularly interest to the haematology lab and the plasma for the chemistry lab.
With this in mind….
The two main results your doctor will be looking for are your blood count and clotting results.
An FBC is normally taken in a purple topped bottle and can tell your doctor a lot.
They will receive a breakdown of your blood cell types, the numbers and size of those present in the sample.
One of the common stomach cancer blood tests is looking for anemia which is a common finding. This is seen in the results by a drop in the hemoglobin, usually abbreviated as Hb. Hb is the oxygen carrier part of your blood.
Once you have been confirmed as anemic, they will want to know what sort of anemia you have.
To determine this, they will look at the MCV on the report. MCV refers to the mean cell volume.
MCV is an indicator of the size of your red cells (average life span 120 days) and in stomach cancer they can be normal, small or large.
Small – this is referred to as microcytic. The most common reason is iron deficiency due to blood loss or not absorbing iron required for cell production.
It usually occurs chronically and if found prior to your diagnosis, it will alert your doctor to the fact that you are bleeding or not absorbing your iron and will require investigation.
They will confirm this by doing a ferritin level or iron studies. Ferritin is a marker of iron in the body and will be low in iron deficiency anemia.
Significant bleeding results in your bone marrow (the part of your bone that produces your blood) working overtime to provide you with the cells you needed to replace those lost.
As a result, immature red cells are released which are larger than a normal blood cell hence the reason why the MCV is raised.
Another common result in stomach cancer blood tests is a low platelet count. It is worrying as it indicates that you are at increased risk of bleeding.
There are many reasons for a low platelet count, but the two main concerns are involvement of your bone marrow by the tumor (bone metastases) or disseminated intravascular coagulation.
Disseminated intravascular coagulation or DIC is a heighten state of clotting due to activation of you clotting or coagulation system.
Initially this means clots can occur anywhere in your body, but as your clotting factors are consumed in the clotting process you can then paradoxically bleed as you can no longer clot.
DIC is common to all tumors, but an unusual complication of stomach cancer. It can also occur after surgery and in many different other conditions.
A more common cause of low platelets in any cancer is from the chemotherapy drugs you receive or other drugs that you may have along the way such as heparin, a blood thinning drug used to prevent clots.
White blood cells are involved in your immunity to infection and their numbers are determined in stomach cancer blood tests.
There are two main types of WBC's – neutrophils and lymphocytes.
In a simplistic way, neutrophils are involved in fighting bacterial infections and lymphocytes fight viral infections.
If raised they can indicate infection, if low this can be due to the chemotherapy that you have received (there are many other causes, but I won’t go in to these to keep it simple).
Chemotherapy isn't a full discriminator of the type of cell it kills and your blood cells are no exception to this.
This is why you can become pancytopenic (all your cell levels can drop) approximately 7 to 10 days following chemotherapy.
When only your white cells are low, it is known as neutropenia. This is a potentially serious side effect from chemotherapy as you are at significant risk of overwhelming infection which is why your oncologist will ask you to monitor your temperature during this the 7 to 10 day window and report urgently should you have a fever.
Your doctor will measure your international normalized ratio or INR. Some labs will measure the prothrombin time or PT as an alternative.
The INR is a measure of the PT against a recognized standard – essentially it gives your doctor a reference of your clotting that is reliable where ever you may be whereas the PT may vary from one lab to another.
A raised INR in stomach cancer bloods tests occurs due to interference with your clotting factor production that occurs in the liver.
The drug Warfarin, which is taken for a variety of conditions that increase your risk of clotting causes a rise in the INR level. The INR is monitored by your doctor whilst you are on the drug.
Vitamin K is a vitamin required for production of the clotting factors D, E, A and K. If you are malabsorbing the vitamin your INR can rise, although this is uncommon.
If your stomach cancer has spread to your liver, in some cases your INR can be raised due to interference in clotting factor production.
There are many tests that can be done, but the ones I am going to mention are the U&E’s and glucose (also known as the Chem 7 or lytes) and the LFT’s or liver function tests.
I will also briefly mention specific stomach cancer blood tests or tumor markers and vitamin B12 too.
U&E’s are an English abbreviation for the urea and electrolytes, but also incorporates the creatinine level too.
In the USA, they are normally referred to as the chem 7 which refers to the 4 electolytes – Na, K, bicarbonate and chloride plus blood nitrogen, creatinine and glucose level). Another term is ‘lytes’ for the electrolytes.
The creatinine and urea are markers of kidney function. Creatinine is produced from the breakdown of creatine phosphate (found in muscle).
Urea is produced during the breakdown of protein in the human body and is removed via the kidneys.
Creatinine and urea is excreted unchanged in the kidney and is thus an indicator of how well the kidneys are working.
A rise in the levels usually indicates kidney failure and in stomach cancer there can be a variety of causes including drugs, DIC and also metastases or tumor deposits either in the kidneys or obstructing urine flow through the tubes known as ureters) to the bladder.
Liver function tests or LFT’s are monitored in stomach cancer blood tests for 2 main reasons:
I won’t go in to the constituents of the LFTs as they are not particularly relevant here.
The glucose levels are measured to look for evidence of diabetes. Whilst this is not strictly relevant to stomach cancer, it can occur rarely as a consequence of metastases or deposits in the pancreas.
Also, if tumor deposits occur in the liver your glucose levels can drop occasionally as the liver fails.
Finally, glucose levels can drop by a condition known as Addison’s disease as a result of tumor deposits in the adrenal glands.
Adrenal glands are involved in the production of the bodies steroids and low levels of steroid will cause a drop in sugar levels as well as a change in your ‘lytes’ (Sodium drops and Potassium rises).
Just to briefly mention another finding in stomach cancer blood tests, the Na levels can be affected. A condition called SIADH or Syndrome of Inappropriate ADH can occur where ADH or antidiuretic hormone.
This hormone stimulates water retention in the kidneys. In cancer, tumors can produce a similar type hormone.
When water is retained, the plasma sodium levels are diluted hence a drop in the sodium level.
It is normally treated by restricting the amount you drink and occasionally with a drug called Demeclocycline, a tetracycline antibiotic which blocks the effect of ADH on the kidney.
Unfortunately there is no specific tumor marker for stomach cancer.
The tumor markers CEA or carcinoembyonic antigen and CA or cancer antigen are often raised in stomach cancer blood tests, but they are not specific enough for stomach cancer as they can be raised in other tumors as well as non-cancer conditions.
There use is really confined to research purposes as a marker of treatment progress.
Whilst not on of the stomach cancer blood tests, HER2 or Epidermal Growth Factor Receptor 2 is a protein on some aggressive stomach cancers and some breast cancers which is measured in the lab and can be thought of as a tumor marker.
It is a protein and its measurement from a tissue sample can be used to determine if you will be sensitive to an anti-HER monoclonal antibody drug called Trastuzumab or Herceptin or Herclon.