ReferencesJC mentioned that the diagnostic accuracy of 24 hour urine collection increases with more collections! Metabolic evaluation of patients with recurrent idiopathic calcium nephrolithiasisWe didn't refer to a particular study on sodium intake and the 24 hour urine but this meta-analysis Comparison of 24‐hour urine and 24‐hour diet recall for estimating dietary sodium intake in populations: A systematic review and meta‐analysis - PMC 24‐hour diet recall underestimated population mean sodium intake.Anna looking up ace i and urinary sodium Effects of ACE inhibition on proximal tubule sodium transport | American Journal of Physiology-Renal PhysiologyThe original FENa paper by Espinel: The FeNa Test: Use in the Differential Diagnosis of Acute Renal Failure | JAMA | JAMA NetworkSchreir’s replication and expansion of Espinel’s data: Urinary diagnostic indices in acute renal failure: a prospective studyHere’s a report from our own JC on the Diagnostic Utility of Serial Microscopic Examination of the Urinary Sediment in Acute Kidney Injury | American Society of NephrologyJC shared his journey regarding FENa and refers to his recent paper Concomitant Identification of Muddy Brown Granular Casts and Low Fractional Excretion of Urinary Sodium in AKIAnd Melanie’s accompanying editorial Mind the Cast: FENa versus Microscopy in AKI : Kidney360 (with a great image from Samir Parikh)JC referenced this study from Schrier on FENa with a larger series: Urinary diagnostic indices in acute renal failure: a prospective study​​Nonoliguric Acute Renal Failure Associated with a Low Fractional Excretion of Sodium | Annals of Internal MedicineUrine sodium concentration to predict fluid responsiveness in oliguric ICU patients: a prospective multicenter observational study | Critical Care | Full TextA classic favorite: Acute renal success. The unexpected logic of oliguria in acute renal failure Marathon runners had granular casts in their urine without renal failure. Kidney Injury and Repair Biomarkers in Marathon RunnersCute piece from Rick Sterns on urine electrolytes! Managing electrolyte disorders: order a basic urine metabolic panelThe Urine Anion Gap: Common Misconceptions | American Society of NephrologyThe urine anion gap in context CJASNExcellent review from Halperin on urine chemistries (including some consideration of the TTKG): Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders - Kidney International ReportsRenal tubular acidosis (RTA): Recognize The Ammonium defect and pHorget the urine pH | SpringerLinkOutlineChapter 13- New part: Part 3, Physiologic approach to acid-base and electrolyte disorders - Do you remember the previous two parts? - Renal physiology - Regulation of water and electrolyte balance- Chapter 13: Meaning and application of urine chemistries - Measurement of urinary electrolyte concentrations, osmolality and pH helps diagnose some conditions - There are no fixed normal values - Kidney varies rate of excretion to match intake and endogenous production - Example: urine Na of 125/day can be normal if patient euvolemic on a normal diet, and wildly inappropriate in a patient who is volume depleted. - Urine chemistries are: - Useful - Simple - Widely available - Usually a random sample is adequate - 24-hour samples give additional context - Gives example of urinary potassium, with extra renal loss of K, urine K should be < 25, but if the patient has concurrent volume deficiency and urine output is only 500 mL, then urine K concentration can appropriately be as high as 40 mEq/L - Table 13-1 - Seems incomplete, see my notes on page 406 - What is Gravity ARF?- Sodium Excretion - Kidney varies Na to maintain effective circulating volume (I’d say volume homeostasis) - Urine Na affected by RAAS and ANP - Na concentration can be used