. Author manuscript; available in PMC: 2015 Nov 1.

Published in final edited form as: Semin Dial. 2014 Jul 10;27(6):586–589. doi: 10.1111/sdi.12283

Table 1.

Laboratory biomarkers of dietary intake; Considerations regarding its use in dialysis patients.

Dietary Intake	Laboratory biomarker	Considerations
Energy	Doubly labelled water	Complex and sophisticated; Unavailable for routine testing; Not validated in dialysis patients. Difficult to evaluate the disappearance of the isotope in the dialysate
Protein	nPNA	In blood or peritoneal dialysate; Fasting; Inaccurate in conditions of anabolism or hypercatabolism; Recommended ranges are: Non-dialyzed CKD: ~0.6–0.8 g/kg/day Hemodialysis: ~1.2 g/kg/day Peritoneal dialysis: ~1.3 g/kg/day
	Creatinine/creatine	Can represent animal protein intake if corrected for creatinine-muscle mass. Inaccurate in conditions of anabolism or hypercatabolism. Because of all this, poor marker.
	Carnitine	Can represent vegetable protein under the assumption of no supplement consumption
	Essential Amino acids	Consider losses into dialysate. Under the assumption of not consuming supplements.
Fat	Fatty acid composition	In serum or adipose tissue (preferred). Provides a measure of dietary fat quality, not fat amount. Reliable estimators of essential fatty acid intake (n-3 polyunsaturated fatty acids, linoleic acid, among others).
Vitamins
	Fat-soluble vitamins (A, D, E and K)	Degradation by light exposure (D). Degraded quickly after extraction (A, E).
	Water soluble vitamins (C and B)	Degradation by light exposure (B). Degraded quickly after extraction (C).
Micronutrients
	Selenium	Valid to detect deficient intake.
	Potassium	Unreliable dietary intake marker in dialysis. High levels can signify underdialysis or alterations in the GI tract (site of potassium elimination). Steroids, ACEIs and potassium-sparing diuretics may raise potassium levels. Acidosis and hyperglycemia promote loss of intracellular potassium and raise potassium levels.
	Iron	Unreliable marker of dietary intake in dialysis patients due to anemia medications.
	Calcium/Phosphate	Unreliable markers of dietary intake in dialysis patients due to CKD-MBD alterations, concurrent medications, and Ca⁺⁺ in the dialysate.