Lupus: How to read your blood tests?
Published 10 May 2021 • By Aurélien De Biagi
On the occasion of World Lupus Day 2021, we'd like to tell you a little more about this rare disease. Lupus is an autoimmune disease mainly affecting women of reproductive age.
What is lupus? How do blood tests help to guide a lupus diagnosis?
Take a look at our article!
What is lupus?
Systemic lupus erythematosus (SLE), often just called lupus, is an inflammatory autoimmune disease. It is characterised by damage to multiple organs by the patients' immune system.
Up until the middle of the 20th century, half of patients saw their life expectancy lower by 10 years. Today, patients can practically live a normal life. Despite this development of treatments, the causes of this disease remain poorly understood even though some risk factors have been identified. For example, we know that a genetic component encourages the appearance of lupus along with environmental factors (tobacco, exposure to sunlight, pesticides, stress, viruses, etc.) or medications (procainamide, quinidine, hydralazine, isoniazid, certain beta-blockers and diuretics).
The effects of lupus will be varied. In these cases, it's to do with a systemic disease (it affects several organs). The major damage will be to the skin ("lupus" meaning "wolf" in Latin and refers to damage in the facial appearance of a patient), joints, kidneys, blood, neurological and vascular.
Biological tests provide a guide for the diagnosis and to rule out any other pathology which could be the cause of similar effects. From these exams, we can name blood and immunological tests visible on a blood test.
Blood tests for lupus
During a blood assessment for the disease, certain effects can be noticed. In some, such as anaemia, they are present in 90% of cases (our list is not exhaustive).
Anaemia is often found with patients affected by lupus. Anaemia is identified by a low haemoglobin level in the blood. Haemoglobin makes it possible for red blood cells to transport oxygen and carbon dioxide towards tissues/organs and towards the lungs. In a healthy person, the haemoglobin level is from 13 g/dL among men and from 12 g/dL among women. In the case of anaemia, this haemoglobin concentration will therefore be less than 13 g/dL for a man and 12 g/dL for a woman.
Another blood symptom is leukopaenia, characterised by a low white blood cell count (immune cells) in the blood.
There are three types:
- Neutrophils (removal of bacteria)
- Eosinophils (removal of parasites and increase in case of allergy)
- Basophils (increase in case of allergy or infection)
- Lymphocytes (viral infection or autoimmune disease)
- Monocytes (increase in case of infection)
The total amount of leukocytes is the total amount of white blood cells in the sample (all types of white cells together). Its value normally ranges from 4 and 10 G/L. When this value falls below the threshold of 4 G/L, it is known as leukopenia. Therefore, leukopenia can be due to the reduction of one or several of these cells.
Note however that in the majority of lupus cases, this is a lymphopaenia. The amount of lymphocytes passes below 1 500/mm3. They become the target of the autoimmune reaction (the immune system attacks itself). In these rarer cases, a neutropaenia (reduction of polynuclear neutrophils) can also be observed (passing below 2 000/mm3).
Thrombocytopaenia is characterised by a low concentration of platelets (cells involved in coagulation and clot formation in case of haemorrhage). The normal range for platelets is from 150 to 450 G/L. Below 150 G/L, it is known as thrombocytopenia. Even though phlebitis is a complication of lupus, it is not due to the amount of platelets but to antiphospholipid antibodies.
Kidney function can also be assessed through a blood test. Creatinine is a molecule produced by the muscles. Due to it being useless for the body, it is removed through the kidneys in urine. So, a high level of creatinine in the blood indicates a lack of kidney function. Normal serum creatinine (concentration of creatinine in the blood) is from 6 to 11g/L for women and from 7 to 14 g/L for men. A higher concentration indicates kidney failure.
During a blood test, an immunological test can also be carried out. During this test, in cases where lupus is suspected, antinuclear antibodies will be looked for. The latter are autoantibodies directed against the patient's own cells. There are several different kinds such as anti-dsDNA antibodies or anti-Ro/SSA.
These antibodies will help guide the diagnosis: if they are not present, the patient cannot be suffering from lupus. On the other hand, if they are present, the patient can be suffering from lupus. They are not specific to lupus, they can also be the result of other autoimmune diseases.
It is worth noting that in most of these antibodies, supplementary proteins can be looked for. The supplement is a part of the immune system which makes it possible to remove waste ("waste collector for the immune system").
It is divided into several parts (C1, C2, C3, etc). With lupus, certain parts of the supplements are less indicated. This is generally due to a self-consumption by the autoimmune response during flare-ups.
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- Lupus - NHS
- Lupus - American College of Rheumatology
- Lupus (SLE) | Causes, symptoms, treatment | Versus Arthritis
- Lab Tests for Lupus | Lupus Foundation of America
- Lupus in Women | CDC
- Lupus | womenshealth.gov - Office on Women's Health
- 10 Frequently Asked Questions About Lupus - Lupus News
- Hematology Glossary - Hematology.org
- Antinuclear Antibodies (ANA) rheumatology.org
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