Protein Catabolism Calculator

How does this protein catabolism calculator work?

This health tool determines the normalized protein catabolic rate nPCR. This parameter helps in the evaluation of dietary protein intake in patients with stable condition who undergo dialysis.

There are four factors taken into account in the protein catabolism calculator:

■ Patient weight – as a clinical parameter, weight provides information on nourishment, any possible weight loss or gain and refines the nPCR Anuric value.

■ ID hours – refers to the interdialytic period in hours.

■ ID BUN rise – refers to the registered change in blood urea nitrogen during the interdialytic period. This can be expressed in mg/dL or mmol/L.

BUN is one of the main indicators of renal function and normal values are between 6 and 20 mg/dL (1.8 – 7.1 mmol/L).

Increased values are caused by high protein diet, decrease in glomerular filtration rate (GFR), congestive heart failure and others. Abnormally low values are indicative of severe liver disease or innapropriate levels of antidiuretic hormone.

■ Urine urea nitrogen – refers to the total amount of urea nitrogen excreted during the interdialytic period.

Its normal values are between 12 and 20 grams per 24 hours. Lower than normal values indicate nephrologic problems or malnutrition while elevated values indicate an increased protein breakdown in the body or too much protein intake.

The recommendation is to input 0.01 in this field in case nPCR is calculated for anuric patients (passage of urine output of less than 100 mL per day)

The two formulas used are the following:

nPCR Anuric = 0.22 + (0.864 x (ID BUN rise in mg/dL)/(ID hours))

nPCR Total = nPCR Anuric + (Urine urea nitrogen in g x 150)/(ID hours x Weight in kg)

The above formulas measure the interdialytic appearance of urea in body fluids and also account for any urea lost through urine during residual renal function.

The protein catabolic rate PCR is the most used parameter in assessing protein intake within hemodialysis units.

A PCR analysis can distinguish between a well-nourished patient adequately dialyzed or a decreased protein intake, as reflection of inadequate dialysis.

PCR is also the protein equivalent of nitrogen appearance PNA and varies directly with the Kt/V. PCR values can offer information on outcomes, for example, according to the National Cooperative Dialysis Study (NCDS), PCR values greater than 1 g/kg/day are associated with lower morbidity.

For dialysis patients, PCR measurements are taken each month, some criticizing the fact that this frequency cannot reflect daily changes in protein intake.

The only criticism received by the method is the fact that it can only be used on stable patients and the assessment of the metabolic stability during dialysis is not regulated. This means that reliable nPCR values cannot be obtained in all patients undergoing dialysis.

Example of a protein catabolism calculation

Taking the case of a patient with the following data:

■ Weight: 86 kg;

■ ID hours: 40 hours;

■ ID BUN rise: 52 mg/dL;

■ Urine urea nitrogen: 15 g.

The normalized PCR values are:

■ nPCR Anuric = 0.22 + (0.864 x 52/44) = 1.343 g/kg/day

■ nPCR Total = 1.34 + (15 x 150)/(40 x 86) = 1.997 g/kg/day

References

1) Jindal KK, Goldstein MB. (1988) Urea kinetic modeling in chronic hemodialysis: Benefits, problems, and practical solutions. Semin Dial; 1:82.

2) Sherman RA, Cody RP, Rogers ME, Solanchick JC (1995) Accuracy of the urea reduction ratio in predicting dialysis delivery. Kidney International; (47)1: 319-321.

3) Koefoed M, Kromann CB, Juliussen SR, Hvidtfeldt D, Ekelund B, Frandsen NE, Marckmann P. (2016) Nutritional Status of Maintenance Dialysis Patients: Low Lean Body Mass Index and Obesity Are Common, Protein-Energy Wasting Is Uncommon. PLoS One; 11(2): e0150012.

4) Panzetta G, Tessitore N, Faccini G, Maschio G. (1990) The protein catabolic rate as a measure of protein intake in dialysis patients: usefulness and limits. Nephrol Dial Transplant; 5 Suppl 1:125-7.