Erythromycin Breath Test Report

Format

A typical report contains the following items:

•  Subject ID
  
•  Date of Testing
  
•  Height of subject - entered in centimeters (provided to MSI)
  
•  Weight of subject - entered in kilograms (provided to MSI)
  
•  BSA (body surface area) - calculated from height and weight, units (meter  squared) (calculated value)
  
•  Baseline breath dpm- measured baseline radioactivity of baseline  breath or control breath sample (measured at MSI)
  
•  20 min breath dpm - radioactivity of 20 minute sample (measured at  MSI)
  
•  CO₂ mmol - amount of carbon dioxide measured for analysis - typical is 2  millimoles.  If less than 2 millimoles is samples, the trapped material is  titrated with acid to calculate the amount trapped.
  
•  Residual dose dpm - amount of radioactivity in dose vial that was not  administered.  We calculate the amount C14 administered using the  residual dose left in the vial.
  
•  C14 metab per min - percent of C14 erythromycin metabolized per  minute at  the 20 minute breath sample. (calculated value)
  
•  C14 metab per hr - percent of C14 erythromycin metabolized per hour  (calculated value).  This value corresponds to the cytochrome P450  enzyme  activity in the liver.  This value corresponds to the area-under- the  curve (AUC)  of C14 exhalation.

The percentage of administered carbon-14 exhaled per minute is calculated from the dpm of the 20 minute breath sample.  The ERMBT assumes an endogenous CO₂ production equal to 5 mmol CO₂/m² body surface area (BSA)/min and 3 µCi (or 6.66 x 10⁶ dpm) injected.  The radioactivity administered must be adjusted to account for some drug left behind in the vial.  The following equation calculates the percent of dose metabolized per minute:

Calculations

% dose metabolized per minute =



Note, if the amount of CO₂ measured is less than 2 mmol but greater than 1 mmol, then the actual amount of CO₂ analyzed in the scintillation counter is used in the above equation in place of 2 mmol.  CO₂ levels less than 1 mmol are not reported.

The final breath test result is expressed as the percent of administered carbon-14 exhaled per hour using a validated exponential equation (1):

Percent C-14 erythromycin metabolized/hr =

  (- 65.988x² + 54.645x + 0.0377) where x = % dose metabolized per minute at   20 minutes

References

Metabolic Solutions, Inc., 460 Amherst Street, Nashua, NH 03063

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