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BIOCHEMICAL TESTS

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Biochemical tests are ordered to diagnose diseases, evaluate treatment plans, monitor medication effectiveness, and evaluate medical nutrition therapy (MNT).

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Biochemical assessment is a controlled process. It involves analyzing control samples, with predetermined analyte concentrations, with every batch of patient specimens. The results obtained from the samples analyzed with a particular batch of patient samples must compare favourably with the predetermined acceptable values.

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Acute illness or injury can trigger dramatic changes in biochemical test results, including rapidly deteriorating nutrition status. However chronic diseases that develop slowly over time also influence these results. Laboratory-based nutritional testing, used to estimate nutrient availability in biologic fluids and tissues.

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Single test results must be evaluated in light of the patient's current medical condition, medications, lifestyle choices, age of the patient, hydration status, fasting status at the time of the specimen collection, and reference standards used by the clinical laboratory.

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Specimen Types Ideally the specimen to be tested reflects the total body content of the nutrient to be assessed. The most common specimens for analysis for nutrients and nutrient-related substances are the following:

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Whole blood: collected with an anticoagulant. if entire content of the blood is to be evaluated; none of the elements are removed; contains red blood cells, white blood cells, and platelets suspended in plasma. Serum: the fluid obtained from blood after the blood has been clotted and then centrifuged to remove the clot and blood cells. Plasma : the transparent liquid component of blood, composed of water, blood proteins, inorganic electrolytes, and clotting factors

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Blood cells: separated from anticoagulated whole blood for measurement of cellular analyte content. Erythrocytes (red blood cells) Leukocytes (white blood cells) and leukocyte fractions Blood spots : dried whole blood from finger or heel prick that is placed on paper and can be used for selected hormone tests.

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Other tissues (obtained from scrapings or biopsy samples) urine (from random samples): contains a concentrate of excreted metabolites Faces (from random samples or timed collections ): important in nutritional analyses when nutrients are not absorbed and therefore are present in fecal material

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Less commonly used specimens include the following: Saliva: is used to evaluate functional adrenal stress and hormone levels Nails: easy-to-collect tissue that may be of value in determining exposure to toxic metals; usually a poor indicator of actual body levels of nutrients Hair: an easy-to-collect tissue that is usually a poor indicator of actual body levels of nutrients; may have value in determining exposure to toxic metals Sweat: classically used for presence of cystic fibrosis

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Type of Tests Measurement of the nutrient, its metabolite or some other products in blood or urine Measurement of the activity of a vitamin-dependent enzyme in erythrocytes. Measurement of an accumulated metabolite whose disposal depends on a vitamin or mineral-dependent enzyme.

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Clinical Serum chemistry panels Biochemical tests are ordered as panels or groupings of tests or as individual tests. The most commonly ordered groups of tests are the- Basic metabolic panel (BMP) and The comprehensive metabolic panel (CMP) that include groups of laboratory tests defined by the Centers for Medicare Services. The BMP includes eight tests used for screening, and the CMP includes all the tests in the basic metabolic panel and six additional tests.

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Basic Metabolic Panel (BMP) Includes : Glucose Calcium Sodium Potassium CO2 Chloride Blood urea nitrogen Creatinine

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Gomprehensive Metabolic Panel (CMP) Includes: Glucose Calcium Sodium Potassium CO2 (carbon dioxide, bicarbonate) Chloride Blood urea nitrogen Creatinine Albumin Total protein Alkaline phosphate (ALP) Alanine aminotransferase( AIIT) Aspartate aminotransferase( AST) Bilirubin

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Clinical chemistry panels used in conjunction with health history physical examination findings, anthropometric data, and dietary intake data can be helpful in screening for nutrition-related health conditions.

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The Complete blood Count The CBC or analysis and description of the red blood cells is often accompanied by a differential count, which enumerates each of the specific classes of leukocytes.

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Urinalysis The urinalysis test is used as a screening or diagnostic tool to detect substances in the urine associated with different metabolic and kidney disorders.

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AnalytesReference Range Significance Serum electrolytes Na+ K+ 135-I45 mEq/L 3.6-5 mEq/L those receiving total parenteral nutrition or who have renal conditions, chronic obstructive pulmonary disease, uncontrolled diabetes mellitus (DM), Glucose70-99 mg/dl (fasting) Fasting glucose >125 mg/dl indicates DM Creatinine0.6-1.2mg/dlIncreased in those with renal disease and decreased in those with PEM (i.e., blood urea n trogen/creatinine ratio >15:1) Constituents of the common serum Chemistry panels

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AnalytesReference Range Significance Blood urea nitrogen or urea 5-20 mg urea nitrogen/dl 1.8-7 mmol/L Increased in those with renal disease and excessive protein catabolism; decreased in those with liver failure and negative nitrogen balance Albumin3.5-5 mg/dlDecreased in those with liver disease or acute inflammatory disease BilirubinTotal bilirubin 0.3-1.0 mg/dL Increased in association with drugs, gallstones, and other biliary duct diseases and hepatic immaturity Total calcium8.5-10.5 mg/dlHypercalcemia, Hypocalcaemia Phosphorous (phosphate) 3-4.5 mg/dlHypophosphatemia associated with hypoparathyroidism and Decreased intake Total cholesterol

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Vitamin D

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AnalytesReference RangeSignificance Haemoglobin concentration 14-17 g/dl (men) 12-15 g/dl (women) In addition to nutritional deficits, may be decreased in those with haemorrhage, marrow failure, or Renal, not sensitive for iron, vitamin B12 Red blood cells3-5.9 x 10 6/mm3 (men) 3.5-5.9 x 106/mm3(women) White blood cell count (WBC) 5-10 x l03/mm3 (>2 yr) Increased (leukocytosis) in those with infection, and Stress, decreased (leucopoenia) in those with PEM, infections or who are receiving chemotherapy or radiation therapy Constituents the Hemogram: complete Blood Count

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Vitamin EExpressed as a ratio to cholesterol Vitamin C>3 mg/L Copper0.8-1.75 mg/L

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Chemical Tests in a Urinalysis AnalytesReference RangeSignificance pH6-8 (normal diet) Acidic in those with a high-protein diet or acidosis and in those with a urinary tract infection Protein2-8 mg/dlMarked proteinuria in those with nephrotic symdrome, severe glomerulonephritis GlucoseNot detected (2-10 g/dl in DM) Positive in those with DM; rarely in benign conditions BilirubinNot detectedIndex of unconjugated bilirubin; increase in those with certain liver diseases KetonesNegativePositive in those with uncontrolled DM Iodine>100g/L

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Vitamin A- meassurement of serum/plasma vitamin A RELATIVE DOSE RESPONSE (RDRT) TEST- percentage increases in vitamin A levels, 5 hours after a small oral dose of 450-1000 g of retinol is measured. the post dose increases in serum vitamin A is inversely related to vitamin A status, because in vitamin A deficiency retinol binding protein(RBP) accumulate in the liver and availability of exogenous vitamin A results in holo RBP. Raised circulating levels of Vitamin A, are maintained depending upon the amount accumulated unbound RBP. RDR greater than 20% is suggestive of vitamin A deficiency.

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Tests for Protein Energy Malnutrition SERUM PROTEIN The first indication of malnutrition is the lowering of serum total proteins and serum albumin. The normal albumin levels are 3.5-5.5 g/dl. During PEM the levels may slow down to 2.0-2.5 g/dl. Serum transferin