Inclusion Criteria:

- Age greater than or equal to 18 years

- Receiving filgrastim at 5mcg/kg ± 10%

- Admitted as an inpatient with an expected stay of at least 24 hours

- Weight is > 190% of their ideal body weight (IBW) for "obese" patients or within 80 -
124% of IBW for matched control patients.

- Patient or their legally authorized representative understands and voluntarily signs
the written informed consent prior to any study-specific procedures. A copy of the
signed informed consent form will be retained by the treating institution.

Exclusion Criteria:

- Patients who have received filgrastim within 24 hours prior to enrollment

- Patients who have received pegfilgrastim within 14 days prior to enrollment

- Hypersensitivity reaction to filgrastim or any related product

- Patients who have taken lithium within 7 days of enrollment

- Serum Creatinine > 1.5 mg/dL

- Patients who are pregnant or breastfeeding

- Patients who are unable to understand and/or render informed consent