Effect of Body Mass on Filgrastim Pharmacokinetics

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