What is the role of lab testing in the workup of hypokalemic periodic paralyses (HypoPP)?

Updated: Apr 30, 2018
  • Author: Naganand Sripathi, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Serum potassium level decreases during attacks but not necessarily below normal. Creatine phosphokinase (CPK) level rises during attacks. In a recent study, transtubular potassium concentration gradient (TTKG) and potassium-creatinine ratio (K/C) distinguished primary hypokalemic PP from secondary PP resulting from a large deficit of potassium. Values of more than 3.0 mmol/mmol (TTKG) and 2.5 mmol/mmol (PCR) indicated secondary hypokalemic PP.

A random urine potassium-creatinine ratio (K/C) of less than 1.5 is indicative of poor intake, gastrointestinal loss, and potassium shift into the cells. If hypokalemia is associated with paralysis, one should consider hyperthyroidism or familial or sporadic periodic paralysis.

Some of the medical conditions associated with hypokalemia are included in the table below (modified from Assadi 2008 [13] ).

Table 5. Medical Conditions Associated With Hypokalemia (Open Table in a new window)

Urine K/C Ratio

Acid Base Status

Other Associated Features

Medical

Conditions

< 1.5

Metabolic acidosis

 

Lower GI loss – Laxative abuse, diarrhea

< 1.5

Metabolic alkalosis

Normal BP

Surreptitious vomiting

>1.5

Metabolic acidosis

 

DKA, type 1 or type 2 distal RTA

>1.5

Metabolic alkalosis

Normal BP

Diuretic use, Bartter syndrome, Gitelman syndrome

≥1.5

Metabolic alkalosis

Hypertension

Primary aldosteronism, Cushing syndrome, renal artery stenosis, congenital adrenal hyperplasia, apparent mineralocorticoid excess, Liddle syndrome

 

ECG may show sinus bradycardia and evidence of hypokalemia (flattening of T waves, U waves in leads II, V 2 , V 3 , and V 4 , and ST-segment depression).


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