Background Laboratory tests are ordered on a daily basis, even though disease probability is often very low. Abnormal results, especially mildly abnormal results, can be difficult to interpret in these circumstances. Further insights into the occurrence of abnormalities can help improve rational test ordering and test interpretation. A study done in Netherlands showed that the laboratory results received for 1621 patients reported that the proportion of abnormal test results increased with increasing pretest probability (from 13.9% to 34.7%) and was 13.4% for tests ordered to reassure the patient and 13.3% for psychosocial diagnoses. Abnormal laboratory test results were frequent, even when pretest probability was low. Physicians should therefore carefully consider when tests are necessary (Houben et al, 2010). Objectives To assess practitioners‟ laboratory investigation ordering practices at KCMC referral hospital from June to July 2016. Methodology This cross sectional study will be conducted in Moshi municipality from June to July 2016. Patients files were used to collect useful information on how clinicians have managed these patients. Result Out of 422 inclusion files which were required to be studied, only 253 (59.95%) were used for this study and the number of clinicians that attended these patients was 45. The results showed that hematology tests (31.3%) are mostly ordered, the most frequently requested, that led to documented action taken with regard to the patient‟s diagnosis or treatment plan, ranged between 15% and 82% and most patients had cardiovascular problems (20.6%). Laboratory department services at KCMC are over utilized, patients are exposed to potential harm from unnecessary tests and treatment and this may expose the clinician to an increased, rather than a decreased, medico legal risk. Patients are exposed to greater risks of complications while they proceed along an unnecessary testing spiral.