BIOCHEMICALASSESSMENT OF NUTRITIONAL STATUS

“Biochemical tests provide the most objective and quantitative data on nutritional status”

• Two types of Tests

• Static

• Functional

Static

measure of a nutrient or its metabolite in blood, urine, or body tissue (an actual measure of the nutrient

Examples: Iron or vitamin A

Limitations: may fail to reflect the overall nutrient status (serum may not reflect level of nutrient in tissues)

Functional

reflects the failure of function or physiologic process of the body as a result of nutritional deficiency (somewhat indirect measure)

Examples: Immune response will be compromised by protein deficiency; visual adaption to dark will be compromised by vitamin A deficiency

Limitations: May be nonspecific; indicates a general nutritional status, but may not allow id of specific nutrients

Protein Status Evaluation

Types of Proteins:

1) Somatic or skeletal muscle (about 75% of body’s protein)

2) Visceral in organs or viscera, erythrocytes, lymphocytes (about 25% of body’s protein)

Evaluation of “protein status” is challenging; no one test or indicator is perfect or without limitation. It is best to evaluate in addition to other nutrition status indicators (anthropometric, clinical, dietary)

Methods to evaluate protein:

Creatinine Height Index (CHI)The body excretes creatinine in the urine as a by-product of skeletal muscle. The amount that is produced is relative to stature (height). This amount can be looked up in references. So. . .

CHI = creatinine (mg) excreted in urine for 24 hours x 100----then divide by the expected 24 hr urine creatinine. It is expressed by a percentage value.

3-methylhistidine is excreted by muscle as well, but this test is not routinely used

Nitrogen Balance Nitrogen is a byproduct of protein breakdown from food we ingest or from our body’s own turnover/breakdown of proteinA person is said to be in “positive nitrogen balance” (a good thing!) when nitrogen intake (from dietary protein intake) exceeds (or is >) than nitrogen loss.

A person is said to be in “negative nitrogen balance” (a serious concern!) when nitrogen losses (from losses of the body’s protein breakdown) exceed nitrogen intake (dietary protein intake).

N2 testing requires collection of urine for 24 hours and knowledge of protein intake for 24 hours. This test is typically completed in very controlled environment.

Methods to evaluate protein in the blood

Albumin (Alb) used in clinical settings to “evaluate” protein status; has half life of 14-20 days (it takes longer to determine if the patient’s diet is adequate in protein). Albumin may “drop” during infection, and can appear low during over hydration. Albumin may appear high during dehydration.

Transferrin binds iron and transports to bone marrow; may drop during infection, wounds, kidney disease.

Prealbumin transports protein that has a half life of 2-3 days. Because of this, it is considered a better indicator of protein status and provides more “up to date response” to nutrition therapy. There are some limitations with interpretation.

Retinol-Binding Protein (RBP) transports protein for vitamin A; similar to prealbumin; has a half life of 12 hours. Levels can decrease with vitamin A deficiency.

IGF (Insulin-like Growth Factor) is a growth promoting peptide produced in response to growth hormone.

Immunocompetence (indirect measure)

1) Nonspecific (skin, mucous membranes, phagocytes, etc) & Antigen Specific Immunity (b-lymphocytes and t-lymphocytes) possibly drop during protein malnutrition

2) TLC – total lymphocyte count (decreases)

3) Delayed cutaneous (skin) hypersensitivity

Evaluating Iron (Fe) Status:Serum Ferritin combines w/ Fe and is stored in liver, spleen &

bone marrow. **Most sensitive and best test to detect early iron deficiency!

Transferrin carries Fe in blood. Associated and used to calculate TIBC (total iron binding capacity). When TIBC goes up, iron level is low. When TIBC goes down, iron level is high.

Hemoglobin (Hgb) is the molecule in RBC (red blood cells) that holds iron, and allows the cells to carry oxygen to the body tissues. (Stage III indicator)

Hematocrit (Hct) expressed as a percentage of RBCs as compared to entire volume of blood

Dietary sources of iron

Heme iron may be found in meat, poultry, fishNon-heme iron may be found in cereal, greens, peas/beans, eggs,

dried fruits;

Vitamin C improves iron absorption

Stages of Iron Deficiency:

I Depletion present with decreased serum ferritin

II Iron deficiency present with decreased transferrin saturated

II Fe deficiency anemia present with decreased hemoglobin (Hgb) and decreased mean corpuscular volume (MCV)

Mean Corpuscular Hemoglobin (MCH) is the amount of hemoglobin in RBCs

Mean Corpuscular Volume (MCV) is the volume of the average RBC; Cell size may go up or down

Low MCV (microcytic anemia or “small red blood cells) is a sign of iron deficiency or even lead poisoning

High MCV (macrocytic anemia or “large red blood cells) is a sign of folate or vitamin B12 deficiency

Types of Blood work or Lab Panels:

CBC (Complete Blood Count) includes RBC, Hgb, Hct, MCH, MCV and can give some idea of anemias

Metabolic Panels or Chem profile/panels (liver profile or comprehensive) includes minerals Na, K, P, Cl, Ca, Alb, total proteins, globulins and liver enzymes (alkaline phosphatase, ALT, AST), byproducts of metabolism (BUN, creatinine, CO2), blood glucose

Lipid Panels include total cholesterol, triglycerides, LDLs, HDLs, VLDLs. We will study more next semester!

Metabolic Panel

ALT (alanine aminotransferase) is a liver enzyme; when elevated may signal a liver problem or disease

Alkaline Phosphatase (ALP) enzyme indicating a problem in liver, bone, placenta, intestine

AST (aspartate aminotransferase) indicates MI, liver disease, drug exposure, musculoskeletal injuriesBilirubin is the pigment in bile, produced from the breakdown of hemoglobin; when elevated may indicate liver problem and results in jaundice

BUN (blood urea nitrogen) is the byproduct of protein metabolism; when elevated can signal renal disease or dehydration

Creatinine becomes elevated with renal disease

Calcium stays very tightly controlled; if low may indicate hypoparathyroidism, renal disease, or pancreatitis; high levels can indicate excessive vitamin D intake. When out of normal range indicates a metabolic problem rather than a true deficiency of dietary calcium.

Carbon Dioxide (CO2) indicates acid/base balance in body. Too high indicates alkalosis; too low indicates acidosis

Chloride (Cl) works with Na to help with acid-base balance and fluid pressure. Low level may indicate alkalosis and low K; High level may indicate kidney disease or heart disease

Glucose (Normal is 70-100 mg/dl) is considered the normal range for a fasting blood glucose level.

If a fasting blood glucose level determines 100-125 mg/dL, the person is considered to have impaired fasting glucose, a type of prediabetes

A random blood glucose test usually will be below 125 mg/dL; when elevated, may signal diabetes.

• A1C test is a common blood test used to diagnose type 1 and type 2 diabetes. The A1C test may be referred to as hemoglobin A1C, HbA1C, glycated hemoglobin, glycosylated hemoglobin.

• The test reflects the average blood sugar level for the past two to three months and measures the percentage of your hemoglobin (protein in RBC that carries oxygen) is coated with sugar (glycated).

• Normal A1C 4.5-6% (5% = 97 mg/dL as estimated average blood glucose level)

• Prediabetes A1C 5.7-6.4% (6% = 126 mg/dL as estimated average BG level)

• Diabetes A1C >6.5% (7%= 154 mg/dL as estimated average BG level)

Phosphorus (P) closely relates to Ca; when high may indicate renal failure; when low may indicate a bone disease (rickets or osteomalacia)

Sodium (Na) maintains acid-base and fluid balance. Low level may be from vomiting, diarrhea, or diuretics, or overhydration; High level may be seen with dehydration. Terms: hypernatremia, hyponatremia

Potassium (K) plays a key role in acid-base and fluid balance; nerve impulses. High level may be seen with renal disease. Low levels may be caused by diuretics, vomiting, diarrhea, eating disorders. Terms: hyperkalemia, hypokalemia

Biochemical Tests of Nutrients:

Zinc (Zn) is involved in enzymes; immune function and wound healing. If depleted can result in growth retardation; if severe may cause dwarfism. Possible tests: metallothionen, hair zinc, urinary zinc

Vitamin C, in reduced form, is ascorbic acid; used in formation of collage, promotion of Fe absorption. Tests: serum, leukocyte levels

Vitamin B6 serves as a coenzyme in reactions; of most concern in elderly and alcoholism; Tests-PLP, plasma PL, total B6 using microbiological assay, Tryptophan Load test (most widely used), Methionine Load test

Folate serves as a coenzyme that transports carbon groups in amino acid metabolism and nucleic acid synthesis.

There are 4 stages of folate deficiency; Low serum folate indicates early depletion; last the tissues begin to deplete. By the time there is full blown deficiency, MCV levels go up (macrocytic anemia) and Hgb goes down.

Vitamin B12 is involved and active in human metabolism. Sources include animal products and fortified grain, soy and plant based meat substitutes.

In order to be absorbed for B12 to be absorbed by the body, it requires an INTRINSIC FACTOR to be secreted by the stomach. When B12 and IF bond, this complex can be absorbed by the ileum.

B12 deficiency is called pernicious anemia. It can result in serious neurological damage. The initial lab indicators for Vit B12 deficiency present the same way as with folic acid deficiency (high MCV and low Hgb). Unless a serum B12 is checked, the true deficiency can be missed.

The Schilling test is used to determine if low B12 level is a result of IF production problem or ileal dysfunction!

Source for slide information

Lee, Robert and Nieman, David. Nutritional Assessment 5th edition. McGraw Hill 2010.

http://www.mayoclinic.org/tests-procedures/a1c-test/basics/results/prc-20012585