title: Urine potassium per hour as a marker for renal potassium losses.
abstract: BACKGROUND
  Hypokalemia, serum potassium (K) < 3.5 mEq/L, is a serious and common clinical problem. The traditional diagnosis of renal potassium losses is 24-hr urine potassium (24U(K)) > or = 20 mEq/day during hypokalemia. Immediate replacement of potassium is often required to prevent complication but may normalize serum K during 24-hr urine collection and render the test inconclusive.
  
  
  METHODS
  The authors examined the ability of urinary indices including 24U(K), transtubular potassium gradient (TTKG), fractional excretion of potassium (FE(K)), urine potassium-creatinine ratio (U(K/Cr)) and spot U(K) and introduced urine potassium per hour during the first 8 hours (U(K)/hr) as a novel index for evaluation of hypokalemia during treatment. Any serum K level > or = 4 mEq/L during urine collection was defined as normalized serum K. In the present study, the final classification of renal K losses in non-normalized 24-hr serum K group was made when 24U(K) > or = 20 mEq/day. In normalized group, the final classification of renal or non-renal K losses was based on the majority of the results of four urine indices including TTKG, FE(K) U(K/Cr) and spot U(K).
  
  
  RESULTS
  Of 61 patients (renal:non-renal = 50:11), 51% and 18% met the criteria of normalized 24-hr and 8-hr serum K. Over all, the U(K)/hr > or = 0.9 mEq/hr can indicate renal K losses with a sensitivity of 96% and specificity of 72.7% compared with the 24U(K) > or = 20 mEq/day of 100% and 54.5%, respectively. In a subgroup of normalized 24-hr serum K, the sensitivity and specificity of U(K)/hr = 95.5% and 77.8% whereas 24U(K) = 100% and 44.4%, respectively
  
  
  CONCLUSIONS
  U(K)/hr is a new practical, simple, and reliable marker that can be applied to evaluate hypokalemic patients during treatment with comparable sensitivity and specificity with 24U(K).
authors.affiliation: Division of Nephrology, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand. rabpd@mahidol.ac.th
authors.forename: Bunyong
authors.initials: B
authors.lastname: Phakdeekitcharoen
authors.forename: Chatchai
authors.initials: C
authors.lastname: Kreepala
authors.forename: Sarinya
authors.initials: S
authors.lastname: Boongird
mesh_terms: D000328:Adult; D000368:Aged; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D011188:Potassium / Q000097:blood / Q000652:urine*; D012372:ROC Curve
chemical_list: D003404:Creatinine; D011188:Potassium