Surgical patients with surprising laboratory data

Preoperative laboratory tests were performed on elective ambulant orthopaedic patients (n = 26) on the afternoon after their arrival in hospital and on the next morning before the operation. Significantly lower concentrations of leukocytes, albumin, total protein, platelets, and total calcium were observed in samples taken in the morning. Posture and chronobiological rhythms may be responsible for these changes. An overnight change in laboratory values may lead to unnecessary further investigations and postponement of surgery. The clinician should be aware of the effects of preanalytical factors on laboratory data.