Clinical Assessment – Laboratory Tests

After completing this section, you will be able to

• Describe tests that may assist with diagnosis of carbon tetrachloride (CCl₄) toxicity.

The laboratory evaluation for patients exposed to CCl₄ should be guided by a careful, thorough history and physical exam. Indiscriminate testing for all exposures is not warranted.

According to the results of the National Health and Nutrition Examination Survey (NHANES), the 95th percentile of blood CCl₄ concentrations was less than 0.005 ng/mL in the 2003-2008 survey years for the U.S. population aged 20-59 years [CDC 2017]. These concentrations reflect the known background exposure of the U.S. population.

While it is technically possible to measure CCl₄ in blood and exhaled air, these tests are not routinely recommended and are very rarely done due to practical and clinical limitations. Interpretation of CCl₄ concentrations is not straightforward. No human data explicitly associate specific organ damage with a given CCl₄ concentration in blood. The clinical response to a given exposure can also vary substantially from person-to-person. Thus, a patient’s quantitative CCl₄ result cannot be correlated with clinical symptoms. Unless needed to confirm recent, excessive exposure, quantitative testing of CCl₄ in biological samples is not indicated because the results do not guide clinical management. If you are concerned that your patient needs such testing, referral to specialty providers in occupational medicine, medical toxicology, or environmental medicine is indicated.

Testing for end-organ damage may be considered for patients who provide a history of potential above background CCl₄ exposures.

Hepatic damage may be assessed with the following studies:

• Alanine aminotransferase (ALT [SGPT]),
• Aspartate aminotransferase (AST [SGOT]),
• Alkaline phosphatase,
• Serum albumin and total protein,
• Prothrombin time (PT) and/or international normalized ratio (INR), and
• Partial thromboplastin time (PTT).

Imaging studies, such as ultrasound or computed tomography (CT) scan, may also be considered.

Renal damage may be assessed with the following studies:

• Blood urea nitrogen (BUN) and serum creatinine (Cr),
• Chemistry panel to check electrolytes,
• Urinalysis (to assess for the presence of protein, blood, casts, or other findings suggestive of tubular or glomerular damage), and
• Complete blood count (CBC) to evaluate for anemia.

Imaging studies, such as renal ultrasound or CT scan, may also be considered.

Respiratory symptoms may be assessed as follows:

• Obtain a chest radiograph to evaluate for pulmonary edema,
• Institute continuous cardiac and respiratory monitoring with continuous pulse oximetry, and
• Consider arterial or venous blood gas analysis as warranted by patient’s clinical condition.

An electrocardiogram (ECG) should be obtained for any patient with acute CCl₄  exposure.

It is critical to consider the role of confounding medical problems (e.g., diabetes mellitus, hypertension, structural or ischemic heart disease) and other exposures (e.g., alcohol, hepatotoxic medications) when interpreting these results.

• Laboratory results need to be interpreted carefully within the context of other pertinent clinical information.