Laboratory tests to determine the cause of hypokalemia and paralysis.
BACKGROUND
Hypokalemia and paralysis may be due to a short-term shift of potassium into cells in hypokalemic periodic paralysis (HPP) or due to a large deficit of potassium in non-HPP. Failure to make a distinction between HPP and non-HPP may lead to improper management. Therefore, we evaluated the diagnostic value of spot urine tests in patients with hypokalemia and paralysis during 3 years.


METHODS
Before therapy, the urine potassium concentration, potassium-creatinine ratio, and transtubular potassium concentration gradient were determined in a second voided urine sample.


RESULTS
Forty-three patients with hypokalemia and paralysis were identified: 30 had HPP and 13 had non-HPP. There was no significant difference in the plasma potassium or bicarbonate concentrations and in the pH of arterial blood between the 2 groups. All but 2 patients in the non-HPP group had urine potassium concentration values less than 20 mmol/L. Although the potassium concentration was significantly lower in the HPP group, there was some overlap. In contrast, the transtubular potassium concentration gradient and potassium-creatinine ratio differentiated patients with HPP vs non-HPP. Although only a mean +/- SD of 63 +/- 36 mmol of potassium chloride was administered in the patients with HPP, rebound hyperkalemia (>5 mmol/L) occurred in 19 (63%) of these 30 patients.


CONCLUSIONS
Calculating the transtubular potassium concentration gradient and potassium-creatinine ratio provided a simple and reliable test to distinguish HPP from non-HPP. Minimal potassium chloride supplementation should be given to avoid rebound hyperkalemia in patients with HPP.
Division of Nephrology, Department of Medicine, Tri-Service General Hospital, National Defense Medical Center, Neihu, Taipei, Taiwan. l521116@ndmctsgh.edu.tw
Shih-Hua
SH
Lin
Yuh-Feng
YF
Lin
Dung-Tsa
DT
Chen
Pauling
P
Chu
Chin-Wang
CW
Hsu
Mitchell L
ML
Halperin
D000328:Adult; D003404:Creatinine / Q000378:metabolism; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007008:Hypokalemia / Q000175:diagnosis* / Q000209:etiology; D008297:Male; D020513:Paralysis, Hyperkalemic Periodic / Q000175:diagnosis*; D011188:Potassium / Q000378:metabolism / Q000652:urine*; D011189:Potassium Chloride / Q000627:therapeutic use
D011189:Potassium Chloride; D003404:Creatinine; D011188:Potassium