Question

While a 71-year-old woman is walking home from
a shopping center, she faints and falls. She is driven home by a friend. When home, she realizes that
she is bleeding from her mouth and is slightly disoriented. She appears injured from the fall, but she does not remember tripping or falling. The woman is taken to a local emergency department. The examining physician determines that there was a loss of consciousness; to determine the reason,
he orders a head CT and ECG and the following laboratory tests: CBC, PT, aPTT, CK, LD, AST,
and troponin T and troponin I. All tests are within normal limits. The woman is sutured for the mouth injuries and admitted to a 24-hour observation unit.

questions

What possible diagnoses is the physician considering?

What laboratory tests would be elevated at 6, 12, and 24 hours if this patient had an AMI?

What isoenzyme tests would be useful with this patient?

Answer 1

Before answering this question I will write down the meaning of the abbreviations:

CT: computed tomography scan, which merges in one image, a lot of x-ray scan slices.

ECG:  electrocardiogram, which is the recording of the heart's electrical activity during a range of time.

CBC: complete blood count used to measure the amount/size/shape of red and white cells as well as platelets, and is used to diagnose any type of hemoglobinopathies.

PT: prothrombin

aPTT: activated partial thromboplastin time

CK: Creatine Kinase

LD: Lactate dehydrogenase

AST: Aspartate transaminase

What possible diagnoses is the physician considering?

By asking a CT scan of the patient's head, the physician was looking for any abnormalities, like tumors, necrosis, hemorrhages or any trauma that could have caused the loss of consciousness. The electrocardiogram was used to detect any abnormality in the heart activity which could have affected the pumping of the blood, and therefore less oxygen was reaching the brain. The complete blood test can be used to diagnose a lot of diseases like leukemia, infections, autoimmune conditions, anemia, etc., but in this case is mainly to check for dehydration, which could have caused the fainting. The prothrombin test together with the activated partial thromboplastin time test and the measure of Aspartate transaminase are run to check the functionality of the liver. Aspartate transaminase is abundant not only in the liver but also in skeletal muscle tissue at a lower level, therefore its increment can be shown in patients with AMI (Acute myocardial infarction = cardiac necrosis) during the first hours, but as is more abundant in the liver is not used to diagnose AMI, on the other side, creatine kinase levels increase in cardiac and skeletal muscle conditions, which makes it useful to diagnose AMI. Creatine kinase is as well abundant in brain tissue, therefore is widely used as an indicator of nerve infraction damage, seizures, strokes, etc. Finally, measurement of lactate dehydrogenase levels can be used to diagnose a wider spectrum of conditions, as is spread in more tissues, hepatocytes (liver), skeletal muscle (more in the heart), kidney, etc. As high levels of it are sustained during AMI for as long as 10 days, it is commonly used to diagnose it. Troponin T and I are subtypes highly related to heart tissue as well. All of the diagnoses were linked to the brain being able to function and receive enough oxygen through the blood, so also heart was checked to see if it was working good enough to pump enough blood to the brain.

What laboratory testes would be elevated at 6, 12 and 24 hours if this patient had an AMI?

AST rises 6-8 hours, peaking at 24 hours after the damage. LD rises 12-24 hours later peaking at 48-72 hours, so this enzyme would also be showing high levels at 12 and 24 hours. Troponin T and I increase 6-12 hours later. Finally, creatine kinase would also be increased after just 3-6 hours, peaking at 16-30 hours.

What isoenzyme tests would be useful with this patient?

For lactate dehydrogenase would be LD-1, for troponin, the subtypes already mentioned T and I, and for creatine kinase CK-MM and CK–MB.

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