More than 1300 blood samples of patients from five different populations were collected, and a complete blood count (CBC) was performed. Out of twenty, fourteen parameters show abnormal result, indicating various blood related diseases. Distribution of blood parameters in different areas show a similar trend, while the values of individual particles greatly vary from site to site, and within the site. A large number of people showed lower than normal values of blood parameter in each area. On the basis of the parameter values, sites may or may not be significantly differ with each other. Metroville site was significantly different from all other sites on the basis of RBC, RDW, WBC and MPV values. It is suggested that on one side poverty, poor hygiene, and pollution are responsible for the various blood related deficiencies/diseases in the population of Karachi, while on the other side consumption of unbalanced junk food and pollution is responsible.