117ACCURACY OF 24 HOUR URINE COLLECTIONS FOR EVALUATION FOR NEPHROLITHIASISR.Allan Jhagroo, K Penniston, S Nakada. UW Madison, Madison, WI Nephrolithiasis is a common problem in the United States affecting approximately 10% of the population at some point in their lives. Recurrence is approximately 50% at 10 years since the initial event. Multiple parameters such as urine calcium, oxalate, and citrate identified on 24 hour urine collections have been implicated as risk factors for recurrence. Identification of these risk factors guide providers in initiation and modification of medical and nutritional recommendations provided to patients. Unfortunately the act of collection of a 24 hour urine sample provides an opportunity for error and thus incorrect diagnosis leading to mismanagement. The purpose of this study was to determine the degree in error of collection that can be expected in kidney stone patients. To evaluate this problem we reviewed 143 twenty-four hour urine studies of patients in our clinic with multiple collections. We were then able to determine averages of their collections and describe the variation seen between collections. In addition patients who have indwelling catheters were reviewed as the expectation was that collections in this population would be more precisely 24 hours. Our findings showed a 34.9 % variation from the mean in the 143 patients. Only 18% variation was noted in our patients with

In conclusion, among our kidney stone patients a large variation in the accuracy of collections exist (34.9%). While only about 18% would seem attributable to physiologic variation. This implies that our conclusions drawn from individual studies may be greatly flawed especially when only a small number of studies are available.

118BMI AS A PREDICTOR OF 24 HOUR URINE COLLECTION ACCURACY R. Allan Jhagroo, KL Penniston, S Nakada UW Madison, Madison, WI Kidney stones burden approximately 10% of the U.S. population. Recurrence is about 50% in a ten year period of time. Many dietary and medical treatments have been found to be successful in reducing recurrence. The use of these interventions is guided by the use of 24 hour urine collections. Unfortunately the reliability of these measures can be poor. To help identify miss-collections the urine creatinine is measured. Ranges listed on common 24 hour test have large ranges for example 800-2000mg creatinine per day. This leaves an enormous opportunity for error and mistreatment. To address this we used the 24 hour collections of near 200 studies of patients who performed multiple collections and determined the mean creatinine and accepted that as the true value. Then using the patients BMI data correlated this to the mean creatinines separately for men and women. What we found is that multiplying the BMI by 62.2 for men and 50 for women produced a number that was within 14% of the accepted true creatinine. In conclusion, using the BMI multiplied by 62.2 which can be rounded to 62 for men and 50 for women can be a useful tool to help determine the accuracy of a 24 hour urine collection. This would likely help prevent under and over diagnosis of conditions related to kidney stone recurrence.

119SPOT SPECIFIC GRAVITY MEASUREMENT IN PREDICTING 24-H URINE VOLUME IN KIDNEY STONE FORMERS R. Allan Jhagroo, Kristina L. Penniston, and Stephen Y. Nakada UW Madison, Madison, WI The supersaturation of urine is a predictor of renal crystal formation and growth. Urine supersaturation is highly dependent on urinary volume, yet many patients have difficulty achieving the minimum target of 2 liters per day on a consistent basis. While insensible losses, may account for some of this difficulty, there appears to be a disconnect in what they perceive to be drinking and actual urine volumes. We investigated the efficacy of specific gravity (SG) measures as a patient education tool to estimate 24-h urine volume. Healthy individuals (n=7) were recruited and trained to use both a urine dipstick (Siemens, Tarytown, NY) and a hand-held hydrometer (Pet Smart, purchased online, typically used in measuring salinity of aquatic habitats) for quantifying the SG of their urine at 4 consistent time points during the day.. Urine output was recorded for volume determination. 24-h urine volumes ranging from 1000-3150 mL were obtained. Individuals were grouped into low-volume (LV, <2 L/d) and high-volume (HV, >2 L/d) groups. Mean SG for each day correlated inversely with 24-h urine volume and was different (p=0.03 for hydrometer and p=0.007 for dipstick) between groups. The mean SG measure for the HV group did not exceed 1.020 at 3 of 4 daily measurement points whereas the SG for the LV never went below 1.015 for those in the LV group but was below that at 3 of 4 time points for those in the HV group. SG measures obtained from urine dipstick and hydrometer were highly correlated (R=0.79). SG measured at specific time points during the day is useful in predicting total daily urine volume and may be a useful patient education and adherence tool. While the hand-held hydrometer was more sensitive in measuring minute differences in SG and easier to read, the urine dipstick, which uses a graded color scheme consisting of 6 categories, appears adequate as well.

120CHEST X-RAYS ARE NOT RELIABLE FOR DIAGNOSING

PNEUMONIA IN HEMODIALYSIS PATIENTS Eric Judd, Mustafa Ahmed, James Harms, Nina Terry, Sushilkumar Sonavane, Michael Allon University of Alabama at Birmingham, Birmingham, AL, USA Both pneumonia (PNA) and pulmonary edema occur commonly in hemodialysis patients. Chest x-rays (CXRs) are used routinely in clinical practice to assist with the differential diagnosis, but their reliability has not been evaluated in this patient population. This study assessed the reliability of the CXR in diagnosing PNA in hemodialysis patients. We identified retrospectively 122 hemodialysis patients admitted with the diagnosis of PNA from the emergency department of a large university hospital during a one-year period. After excluding 54 patients (37 with missing dialysis records, 15 requiring continuous renal replacement therapy, and 2 without initial chest x-rays), the remaining 68 patients were analyzed. Two experienced radiologists who were blinded to the patients’ clinical course and subsequent imaging studies independently interpreted the admission CXRs for the presence of PNA or pulmonary edema. Two internal medicine-trained physicians independently determined the presence of PNA and pulmonary edema after reviewing the entire hospitalization record. We assessed the level of agreement among the observers.

Table 1: Observer Agreement PNA Pulmonary Edema Radiologists 40/68 (58.8%) 38/68 (55.9%) Clinicians 41/68 (60.3%) 52/68 (76.5%) All Observers 12/68 (17.6%) 22/68 (32.2%) In conclusion, there is substantial disagreement between experienced radiologists on the CXR diagnosis of PNA and pulmonary edema in hemodialysis patients, perhaps reflecting uncertainty about the etiology of the pulmonary infiltrate in this population. Clinicians more frequently agreed on the diagnosis of pulmonary edema than of PNA suggesting that PNA is more difficult to diagnosis clinically. The admission diagnosis of PNA in hemodialysis patients may frequently be incorrect.

NKF 2012 Spring Clinical Meetings Abstracts

Am J Kidney Dis. 2012;59(4):A1-A92A44