To determine whether untreated mild coagulopathy in patients with no evidence of clinical bleeding is associated with an increased risk of hemorrhage after paracentesis or thoracentesis, retrospective examination was conducted of 608 consecutive procedures for which prothrombin time (PT), partial thromboplastin time (PTT), platelet (Plt) counts, and preprocedure and postprocedure hemoglobin concentrations were available. There was no increased bleeding in patients with mild to moderate coagulopathy (defined as PT or PTT up to twice the midpoint normal range or pit count of 50 to 99 x 10(3) per microL [50-99 x 10(9)/L]). However, patients with markedly elevated serum creatinine levels (6.0 to 14.0 mg/dL [530-1240 mumol/L]) had a significantly greater average hemoglobin loss (-0.82 +/- 1.3 g/dL [-8 +/- 13 g/L], n = 11) than patients with normal serum creatinine levels (-0.12 +/- 0.88 g/dL [-1 +/- 9 g/L], n = 450) (p = 0.011). Overall, the frequency of bleeding complications requiring red cell transfusions was very low: 0.2 percent of events. The most common diagnosis for patients who had paracentesis was alcoholic liver disease (72%); for those having thoracentesis, it was infection (37%). It can be concluded that, for these patients, prophylactic plasma or platelet transfusions are not necessary. Patients with markedly elevated serum creatinine deserve close postprocedure observation.