APS 101 takes you through the ins and outs of APS, providing facts and key information to help you better understand the disease.
APS 101 is written by Jacqueline Madison, MD, Assistant Professor in the Division of Rheumatology and member of the Jason Knight Lab. In this month’s edition, Dr. Madison discusses what lab tests you should expect when first being evaluated for APS.
What lab testing is done for a new evaluation for APS?
Any patient undergoing an evaluation for APS will likely see a rheumatologist, a hematologist, or both. In a clinic appointment with one of these specialists, the patient should expect that they will have blood drawn for lab testing. Lab tests are part of how we make a diagnosis of APS.
There are the three standard antiphospholipid antibody tests that are part of the classification criteria (refer to APS 101 from December 2021), but there are some other tests, too. An example is anti-phosphatidylserine/prothrombin (anti-PS/PT) antibody. This blood test is often seen in patients with APS and is sometimes seen even when the other, more typical antiphospholipid antibody tests are negative. Over time, tests like this are likely to become more standardized and widely used.
What else, though? What other lab testing is important?
- It is important to assess the patient’s full health when we are evaluating for APS. We especially look at the health of the kidneys, which is sometimes only apparent by testing blood and urine. In blood, we look closely at the creatinine, a test of how well a kidney is filtering the blood. We test for blood in the urine and especially urine protein, which should not be present in urine if a kidney is doing its job.
- Some patients with APS can have problems with anemia (low hemoglobin), low white blood cells (the infection-fighting cells), or low platelets, so we make sure to order a complete blood count, or CBC, to look at these levels.
- The doctor may send some additional tests to look at whether a patient is forming any active clots. This can be especially important when we are concerned for microvascular (meaning in tiny blood vessels) clots as these are too small to be detected by ultrasound or other imaging studies. The key test here is D-dimer, which is elevated when the body is actively clotting.
- For patients on the blood thinner warfarin (also known as Coumadin), an INR tells us just how “thin” the blood is. There is also a special test called chromogenic factor X that we send in patients with APS to confirm the INR is accurate.
- In rheumatology, we do a lot of testing for other autoimmune diseases because about half of patients with APS have another autoimmune disease, and sometimes this is not recognized until after the diagnosis of APS is made. The most common example is lupus, so we do a lot of blood testing for lupus when we are first evaluating patients. These tests include an ANA (antinuclear antibody), anti-double-stranded-DNA antibody, complements called C3 and C4, and a panel of other antibodies (including anti-Sm and anti-chromatin).
- Depending on the patient’s symptoms, we may test for other diseases, too, like rheumatoid arthritis or vasculitis.
- Finally, if you come to an APS research center, you may be offered the chance to participate in research. In that case, sometimes the researchers may ask if it is okay to draw extra tubes of blood that can go towards better understanding different aspects of APS.
So don’t be surprised if you have a blood draw at your first clinic appointment for APS! After the initial evaluation, there is less blood drawn at follow-up appointments, but still ongoing monitoring to make sure you are on the correct path with regards to diagnosis and treatment.
Contributed by Jacqueline Madison, MD
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