Urine Potassium Per Hour as a Marker for Renal Potassium Losses
Bunyong Phakdeekitcharoen MD*, Chatchai Kreepala MD*, Sarinya Boongird MD*
Affiliation : *Division of Nephrology, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
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 (24UK) > 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.
Material and Method: The authors examined the ability of urinary indices including 24UK, transtubular potassium gradient
(TTKG), fractional excretion of potassium (FEK), urine potassium-creatinine ratio (UK/Cr) and spot UK and introduced urine
potassium per hour during the first 8 hours (UK/hr) as a novel index for evaluation of hypokalemia during treatment. Any
serum K level > 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 24UK > 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, FEK, UK/Cr, and spot UK.
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 UK/hr > 0.9 mEq/hr can indicate renal K losses with a sensitivity of 96% and specificity of 72.7% compared with
the 24UK > 20 mEq/day of 100% and 54.5%, respectively. In a subgroup of normalized 24-hr serum K, the sensitivity and
specificity of UK/hr = 95.5% and 77.8% whereas 24UK = 100% and 44.4%, respectively.
Conclusion : UK/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 24UK.
Keywords : Hypokalemia, Urine potassium per hour (UK/hr), 24-hour urine potassium (24UK), Transtubular potassium gradient (TTKG), Fractional excretion of potassium (FEK), Urine potassium-creatinine ratio (UK/Cr)
