IS SERUM CREaTInInE ManDaTORy pRIOR TO COnTRaST EnhanCED COMpUTED TOMOGRaphy?

Introduction: Contrast-enhanced Computed Tomography (CECT) is an imaging technique to diagnose many clinical manifestations. Contrast media used in CECT can lead to contrast induced nephropathy (CIN). Hence, screening of serum creatinine (SCr) level prior to CECT is commonly practiced as it is considered to be an indicator for the risk of Contrast Induced Nephropathy (CIN). But, it adds up extra cost and also increases duration for investigation. The purpose of this study is to find out, if SCr screening can be skipped among certain group by medical history related to risk factors of CIN.


InTRODUCTIOn
CT examinations are often done using contrast media (CM). Such examinations are called contrastenhanced CT (CECT). 1 Contrast media are diagnostic agents used to enhance or create the necessary visual contrast in an image between the organs, vessels, or tracts in which they are present and the surrounding tissue in the body. Therefore, it is possible to visualize difference between normal and pathologic conditions. 2 Commonly barium or iodine is used as positive CM due to their high density. Barium is used only for gastrointestinal (GI) system while iodine can be used for all other system including GI system also. 3 ICM are excreted unmetabolized by glomerular filtration through kidneys. Approximately 12% of injected dose is found in urine at 10 minutes, 50% at one hour, 83% at 3 hours and about 100% within 24 hours. Less than 1% of the injected dose is excreted through other routes such as liver and small bowel4. Non-idiosyncratic or non-anaphylactic reactions are usually dose dependent and specific for any substance. This type of reaction also includes contrast-media induced nephropathy (CIN). 5,6 Most of the medical institutions advise routine screening of serum creatinine (SCr) prior to CECT examinations in order to check the functional status of kidney so that incidence of non-idiosyncratic CIN can be minimized. 7 The normal range of creatinine may vary among laboratories. Elevated creatinine level may indicate that the kidney is not functioning properly or may be damaged. 8,9 Routine SCr test is not required for all patients undergoing CECT, considering the fact that contrast is not always the factor responsible for creatinine elevation. 10 CECT examinations are done for critical diagnostic study which should not be delayed due to excessive concern regarding the possibility of contrast induced nephropathy. 11 Major risk factors should be screened out properly and if creatinine testing is required, a creatinine level obtained prior 6 weeks is sufficient for most examinations. 12 Moreover, Patients may get annoyed due to extra prick while taking sample again. The laboratory cost of obtaining a creatinine level at our institution is significant for poor nepalese and it takes about 2 hours for receiving the lab report. Though the cost and time of reporting may vary among different institutions, this can cause delay in the examination as well as reporting of the examination. Eventually, it is inconvenient for the patient for another laboratory test and there is loss of lots of time. So, we are in need to ask "Are screening serum creatinine levels necessary for all patients prior to contrast enhanced CT examinations?"

MaTERIalS anD METhODS
Descriptive cross-sectional study design was used over 250 samples (59% female and 41% male) undergoing contrast enhanced computed tomography in Chitwan Medical College over 2 months of time between June 2016 to September 2016. Age of patients varied from 10 years to 92 years. All the cases were included except for noncontrast CT scans and emergency CT scan. Pre -scan serum creatinine (SCr) level of each patient undergoing CECT examination was obtained and, survey of medical history regarding risk factors for CIN was also taken in each case where investigator was directly involved in data collection. Individuals having SCr level below 1.5 mg/dl (133μmol/L) were categorized to be normal and above that were categorised to be abnormal. Likewise, risk factors included in study were renal diseases, Diabetes, Chemotherapy, Hypertension, Chemotherapy + Diabetes, Diabetes + Hypertension, Renal disease + Hypertension. Data was entered into a computer analyzed by IBM SPSS 20 after due reviewing of accuracy and completeness in terms of descriptive statistics. MS-Excel was also used for minor calculations and chart designing RESUlTS

Age Group
Number of patients

COnClUSIOn
In this study 68% of total (250) patients were found normal SCr level without any risk factors for CIN and among 3% abnormal categorized patients (SCr ≥1.5mg/dl)) 71% (5 of 7) were identified with risk factors. Among the patients with risk factor which were 76 in number, 5 patients (6.5%) were found to be abnormal with elevated sCr where those having renal disease was predominant with 3 patients (~4%) while hypertension with diabetes was just single (1.3%) and hypertension with renal disease was also one (1.3%). This suggests that screening of baseline SCr level should be prescribed only to those patients who acquire any of the identifiable risk factors for CIN. Those patients, who are not identified with any of the associated risk factors, can be administered with contrast media without screening for SCr level. This can reduce many challenges while checking patient's creatinine status, such as patient's booking delays, extra cost and time, additional pricking while taking blood sample. This practice can also increase the departmental throughput and efficiency of service.

RECOMMEnDaTIOnS
The following would be recommendations to the CT department: 1. The patients scheduled for CECT should be properly surveyed with following risk factors: a. Renal disease/insufficiency b. Diabetes c. Hypertension d. Chemotherapy 2. If any of the above risk factors are not present, contrast media can be administered without screening for serum creatinine level.