Lab testing is in the case of myocarditis focused on the detection of biomarkers of heart muscle damage and the intensity of any inflammatory processes. Laboratory results along with imaging methods provide valuable information for determining the patient´s state and suitable treatment.

CARDIAC SPECIFIC ENZYMES

Levels of so called cardiac specific enzymes (molecules within heart cells) are watched in myocarditis patients. Medical experts watch several of them – troponin, myoglobin, myocardial (heart) creatine kinase (CK-MB). Each of the enzymes has its certain function in the heart.

Troponin has together with other molecules an important role in heart muscle contraction. Troponin is not usually detected in blood except in very small amounts. It is released into the blood during the damage to heart cells. The level of troponin in the blood indicates the extant of heart muscle damage, rising level of troponin corresponds to rising myocardium damage. In contrast to a heart attack, troponin levels do not rise and fall rapidly. Its level rises and falls in myocarditis mostly slowly and it can be detected in blood even a long time after myocarditis itself, but in smaller amounts. Troponin does not have to be released during myocarditis. Nevertheless, it is in total a reliable marker in the diagnostic of myocarditis.

Myoglobin is a molecule which binds and transfers oxygen in muscle cells (of the heart and other muscles) and it also causes its red colour. The level of myoglobin is also observed in acute myocarditis. The problem is that myoglobin can be observed in blood even during and after damage to other muscles, big physical strain or kidney disease. Because of this, other cardiac specific enzymes are also tested.

CK-MB (myocardial creatine kinase) is a molecule (enzyme), which participates in creating energy reserves in muscle cells. It occurs in several forms, including myocardial form. During myocarditis, the level of CK-MB in the blood is usually normal.

Picture 17: Myoglobin (author: Thomas Splettstoesser)

SIGNS OF INFLAMMATION

Many signs of ongoing inflammation can be observed during myocarditis. However, none of them can confirm the disease. More likely they pointe to the fact that inflammation is taking place in the body and this can be quantified.

The best known inflammatory markers is CRP (C-reactive protein). It is a protein which “marks” agents of the disease for elimination by the immune system. A rapid rise of CRP above normal level points more often to bacterial infection, a lower rise is more often observed in viral infection. It is more likely an indicative test, which shows that an inflammation is taking place in the body.

Another sign of inflammation appearing in approximately a quarter patient is an increased total number of white blood cells (leucocytosis). Specifically, it means that the number of white cells is greater than  10 x 10^9 of white blood cells per litre of blood. In viral and bacterial myocarditis, increased amounts of certain types of white blood cells (specifically lymphocytes and neutrophils) are observed and in hypersensitive myocarditis eosinophils (see Chapter What´s going on in the body).

Other sign of inflammation, observable in half of myocarditis cases, is increased sedimentation of red blood cells (erythrocytes). This test indicates how quickly red blood cells fall in a test tube with blood (see Picture 18).

Picture 18: Sedimantation of red blood cells (author: Tristanb)

AUTO-ANTIBODIES AND OTHERS

The test of auto-antibodies (antibodies against tissues of own body), alternatively of other molecules, is another test that may be done at patients with myocarditis. The importance of this test is not based on a diagnostics of myocarditis, but in confirmation or reject any suspicion of some autoimmune disease or disorder. It is a test of, for example so called antinuclear antibodies (ANA), aimed at the nucleus of cells; and the rheumatoid factor, what is an antibody against a part of immunoglobulins – antibodies (more in chapter Treatment possibilities). Further, it could be an antibody against myosin (one of molecules forming the basis of muscles, including the heart muscle) and against heart receptors, which increases heart frequency (so called β1 adrenergic receptors).

Cytokines are other molecules that may be tested in association with myocarditis, however mostly in case of research. Cytokines are molecules that influence the immune response of the body to agents (cause) of myocarditis (see chapter Definition of myocarditis). Some of them are for example TNF-α and interleukin IL-1 (molecules that provoke immune reaction and cause fever) and interleukin IL-10 (it participates on regulation of immune response to the immune system do not “overdo” the reaction against the disease agent). Another molecule is so called Fas ligand, what is a substance of the membrane – the surface of cells, which together with troponin informs about the level of cells damage. High levels of these molecules are often observed at myocarditis with a dramatic course.

MICROBIOLOGY AND VIROLOGY

It is a test of blood, alternatively either a rectum or neck swab, when medical experts try to determine the cause of myocarditis. Sometimes even secretions of the upper respiratory tract are tested. These tests are however very often falsely negative – the cause of the disease is not detected by these methods.

Mostly physicians are looking to distinguish between viruses and bacteria with the use of so called cultivation (microorganism, in this case mainly bacteria, is “grown” to detect which type it is). Further, physicians are looking for the presence of antibodies against cases of myocarditis (see chapter Causes of myocarditis) and in the case of viruses even the PCR method is used, when the presence/absence of DNA or RNA of a certain virus is confirmed.

The problem is that some causes are detectable only for a limited time and these tests are in total complicated by different factors. In total, the cause of the disease is detected in only about 4% of patients with myocarditis.

Picture 19: Cultivation (author: 43trevenque)

Authors of the opening picture: 43trevenque; Bill Branson