Biochemical Indicators FN 115‐Nutritional Assessment and Epidemiology
IRON STATUS 2
C. P. Fernandez
Stages of Iron Depletion and Biochemical Tests Used to Identify Them
Iron Deficiency “State in which there is insufficient iron to maintain the normal physiological function of tissues such as the blood, brain, and muscles.” C. P. Fernandez
Descriptive Term Biochemical Tests
First
Depleted iron stores Iron deficiency w/o anemia
Second
Iron‐deficiency anemia
Third
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Serum ferritin level Transferrin saturation Erythrocyte protoporphyrin Hemoglobin Mean corspuscular volume (MCV)
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Cont.
Serum Ferritin
Good indicator of body iron stores Useful in assessing total body iron
load 1 ug/L serum ferritin is equivalent to 8‐10 mg stored iron for an average‐ size adult
C. P. Fernandez
Stage
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1.
2.
Most specific test for iron deficiency 2 major exceptions for use: significant or chronic i ifi t h i inflammatory conditions and disease processes that cause tissue destruction C. P. Fernandez
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Cutoff values indicative of iron deficiency
Transferrin receptors
Age (yr)
Serum Ferritin (ug/L)
1‐2
‐
3‐4
<10
5‐10
<10
11‐14
<10
15‐74
Transferrin receptors on the surface of the erythrocyte precursor increase when the supply of iron is inadequate for the production of hemoglobin d i fh l bi Cutoff value in defining elevated transferrin receptor level based on normal values for adults is >8.0ug/L
<12 C. P. Fernandez
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Cutoff values indicative of iron deficiency
Erythrocyte protoporphyrin Precursor of hemoglobin and
1‐2
Erythrocyte Protoporphyrin (umol/L RBC) >1.42
3‐4
>1.33
5‐10
>1.24
11‐14
>1.24
Age (yr)
becomes elevated when the iron supply is insufficient supply is insufficient Can be used as a screening test in children and adults
15‐74 C. P. Fernandez
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>1.24 10
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Hemoglobin levels below which anemia may be considered to be present (WHO)
Hemoglobin
Age and Sex
Iron‐containing molecule found in
RBC capable of carrying oxygen Index of blood Index of blood’ss oxygen carrying oxygen carrying capacity (g hemoglobin/dL blood) Most widely used screening test for IDA
Children: 6 mos – 6y y – 14y y 6.1y Adult: Males Females (nonpregnant, non-lactating) Pregnant Women Lactating Women
C. P. Fernandez
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Normal Hb Level (g/dL) 11.0 12.0 13.0 12.0 11.0 12.0
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Epidemiological criteria for assessing severity and magnitude nutritional anemia in population groups (FAO/WHO, 1992) MAGNITUDE Parameters
High Moderate Low
Percent of population with Hb Percent of population with Hb less than the above cut‐off > 40 points especially women and children Percent of population with Hb less than 7g/dL especially > 10 women and children
10‐39
1‐9
1‐9
<1
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RBC Calculated by dividing Hg level by Calculated by dividing Hg level by RBC count Reference values ≈ 26‐34pg
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Volume of average RBC Calculated by dividing hematocrit
Average concentration of Hg in the
value by RBC count Normal range = 80‐100fL Normal range 80 100fL Factors increasing MCV: Folate and B12 deficiency, chronic liver disease, alcoholism, cytotoxic chemotherapy
average RBC Calculated by dividing Hg value by Hematocrit value Normal range = 320 ‐ 360g/L (32 ‐ 36dL) 15
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Models Assessing Impaired Iron Status
Transferrin saturation
Model Measurements Used Ferritin Model Serum ferritin Transferrin saturation Erythrocyte protoporphyrin Mean MCV corpuscular Transferrin saturation volume (MCV) Erythrocyte protoporphyrin model
Reflects adequacy of iron
transport to tissue Serum transferrin Serum transferrin of <16% is of <16% is associated with iron deficiency
C. P. Fernandez
MCH is the amount of hemoglobin in
Mean Corpuscular Volume
Mean Corpuscular Hemoglobin Concentration
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Mean Corpuscular Hemoglobin
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Models Assessing Impaired Iron Status Model Measurements Used Four‐variable MCV or serum ferritin model Transferrin saturation Erythrocyte protoporphyrin Hemoglobin Hemoglobin percentile shift Transferrin saturation model Erythrocyte protoporphyrin C. P. Fernandez
IODINE STATUS 19
Biochemical Indicators
Good marker of previous day’s dietary iodine intake Data can be used only for making a population based estimate population‐based estimate Iodine concentration in early morning urine specimen provides adequate assessment of a population’s iodine status
Thyroid Stimulating Hormone
(TSH) Thyroglobulin (Tg)
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Epidemiological criteria for assessing severity of IDD based on median urinary iodine levels Median value Severity of IDD (μg/l)) (μg < 20 Severe IDD 20‐49 Moderate IDD 50‐99 Mild IDD No deficiency > 100 C. P. Fernandez
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Urinary Iodine
Urinary Iodine
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Thyroid stimulating hormone (TSH)
Iodine levels are low Pituitary gland stimulates the release of TSH 23
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4
TSH…
Thyroglobulin (Tg)
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Enhanced turnover of thyroid f h id cells
°
°
Insufficient iodine intake induces induces proliferation of thyroid cells
and adequacy of thyroid hormone hormone Best diagnostic for determining hypothyroidism
°
Directly reflect the availability
Release Tg into the serum
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C. P. Fernandez
Summary of IDD prevalence indicators and criteria for a significant public health problem
Median Tg Different assays may have different
Target Population Median Median School age 50 School age 50‐99 99 urinary iodine child level (ug/L) TSH >5mU/l 3.0‐ Neonates whole blood 19.9% Median Tg Children & 10.0‐ (ng/ml serum) Adults 19.9
normal ranges Normal (children and adults) Normal (children and adults) = 10ng/ml
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Severity of public health problem (prevalence) Mild Moderate Severe
Indicator
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C. P. Fernandez
20 49 20‐49
<20
20.0‐ 39.9% 20.0‐39.9
> 40.0% > 40.0
WHO/NUT/94.6
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Indicators for the assessment of Vitamin A status at the subclinical level Serum retinol Serum retinol‐binding protein (RBP) lb d ( ) RBP/TTR molar ratio
VITAMIN A STATUS C. P. Fernandez
RAG hydrolysis test
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Serum Retinol Level
Serum Retinol Level is under homeostatic control Reflects stores only when they are very high or very low Best used when frequency distribution can Best used when frequency distribution can provide useful information… … about the status of a population …about response to an intervention programme
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WHO biological indicators of subclinical vitamin A deficiency in children 6‐71 months of age (McLaren and Frigg, 2001) Prevalence below cut‐off to define a public health problem and its l l fi level of importance Indicator (cut‐ Mild Moderate Severe off) Serum retinol > 2‐<10% > 10‐<20% > 20% (<0.70μmol/l) C. P. Fernandez
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0.70μmol/l • “low” value • Considered consistent with the presence of a subclinical deficiency status C. P. Fernandez
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Serum retinol‐binding protein (RBP) Correlates closely with serum
retinol Measured using fluorometer
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RBP/TTR (transthyretin) molar ratio
RAG (retinoyl β‐glucuronide) hydrolysis test
Introduced to assess vitamin A status in the presence of inflammation Low molar ratio of RBP/TTR can distinguish VAD in the presence of infection
RAG is a naturally occurring
C. P. Fernandez
metabolite of Vitamin A In a study, RAG orally administered to rats with VAD retinoic acid appears in the plasma in high concentrations 35
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Assessment of Body Reserves
Indirect assessment of liver
Indirect assessment of liver stores
stores…
Relative dose response (RDR)
apo‐RBP accumulates in the liver when retinol is in short supply short supply
Modified relative does response
(MRDR) Serum 30‐day dose response Deuterated‐retinol‐dilution technique C. P. Fernandez
Once retinol is available RBP is released into the circulation 37
Relative Dose Response “When stores of retinol are high,
plasma retinol concentration is little affected by oral administration of Vitamin A But when reserves are Vitamin A. But when reserves are low, the plasma retinol concentration increases markedly, reaching a peak 5h after oral dose.” C. P. Fernandez
1
2
3
• Fasting serum retinol is measured (A0) • 450‐1000mg retinyl ester is given orally
• 5 hours after dosing, serum retinol is measured (A5) retinol is measured (A5)
•RDR = (A5‐A0) x100/A5
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Limitations of RDR
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WHO biological indicators of subclinical vitamin A deficiency in children 6‐71 months of age (McLaren and Frigg, 2001)
5 hours waiting period Need to draw 2 blood samples
Indicator (cut‐off) RDR (>20%) C. P. Fernandez
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Prevalence below cut‐off to define a public health problem and its l l fi level of importance Mild Moderate Severe <20%
> 20‐<30%
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> 30% 42
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Modified Relative Dose Response (MRDR)
Cont.
Uses a metabolite of vitamin A, 3,4‐
• Oral dose of DR 1
didehydroretinyl acetate (dehyroretinol) (d h i l) Dehydroretinol binds to RBP and appears in serum after test dose is liver reserves of vitamin A are low C. P. Fernandez
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Modified Relative Dose Response
3
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WHO biological indicators of subclinical vitamin A deficiency in children 6‐71 months of age (McLaren and Frigg, 2001)
>0.06 – marginal or poor vitamin A status <0.03 – adequate vitamin A status
Indicator (cut‐off) MRDR (ratio > 0.06) 45
Prevalence below cut‐off to define a public health problem and its l l fi level of importance Mild Moderate Severe <20%
> 20‐<30%
C. P. Fernandez
> 30% 46
WHO biological indicators of subclinical vitamin A deficiency in children 6‐71 months of age (McLaren and Frigg, 2001)
Serum 30‐day dose response (+S30DR) Similar to RDR but…
… second blood sample taken 30‐45 p days after the first Used at the population level and in monitoring the effectiveness of interventions C. P. Fernandez
• MRDR = SDR/SR
C. P. Fernandez
Dehydroretinol:retinol
C. P. Fernandez
2 • Blood test (4‐6 h hours after dose)
Indicator (cut‐off) +S30DR (ratio > 20%) 47
Prevalence below cut‐off to define a public health problem and its l l fi level of importance Mild Moderate Severe <20%
> 20‐<30%
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> 30% 48
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Deuterated‐retinol‐dilution technique
Breast milk Vitamin A concentration
Uses stable isotope of hydrogen – deuterium Used increasingly in research Extent of dilution of the labeled tracer relates to the amount of endogenous reserves
Proposed to be used as an indicator
of vitamin A status of a communityy Concentration of vitamin A in the breast milk of undernourished mothers is low 49
C. P. Fernandez
WHO biological indicators of subclinical vitamin A deficiency in children 6‐71 months of age (McLaren and Frigg, 2001)
Average Breast milk concentrations Vitamin A‐ sufficient populations
Vitamin A‐deficient population
1.75‐2.45μmol/L
<1.4μmol/L
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C. P. Fernandez
Indicator (cut‐off) Breast milk retinol (< 1.05μmol/L or <8μg/gmilk fat)
Prevalence below cut‐off to define a public health problem and its level of importance Mild Moderate Severe <10%
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> 10‐<25%
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> 25%
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Protein Principal compound of body
structure and function Not stored in a non‐functional form Not stored in a non functional form Gain or loss of protein represents equivalent gain or loss of function
PROTEIN STATUS C. P. Fernandez
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Biochemical assessment of protein status: two compartment model Somatic and visceral protein Somatic protein –
skeletal muscles Visceral protein – organs, erythrocytes, granulocytes and lymphocytes C. P. Fernandez
Rate of protein synthesis or anabolism = Rate of protein degradation or catabolism Positive Nitrogen Balance – Positive Nitrogen Balance nitrogen nitrogen intake exceeds nitrogen loss Negative Nitrogen Balance – nitrogen losses exceed nitrogen intake
Normal Half‐life Function Value Mean (+ ( SD or Range) 12‐20 Maintain 45 (35‐50) plasma oncotic days pressure; carrier for small molecules C. P. Fernandez
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Based on the assumption that
decreases in serum concentrations are due to decreased in liver production A consequence of limited supply of amino acids
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Serum Proteins Used in Nutritional Assessment
Albumin
– used for estimating body muscle mass When compared with a standard based on stature, it can be used to estimate lean body mass
Serum Proteins
Serum Protein
24‐H urinary creatinine
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Nitrogen Balance
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Creatinine excretion and Creatinine‐height index
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C. P. Fernandez
Serum Protein
Transferrin
Prealbumin
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Normal Half‐life Function Value Mean (+ SD or Range) 2.3 (2.6‐ 8‐9 days Binds iron in plasma and plasma and 4 3) 4.3) transports to bone marrow 0.30 (0.2‐ 0.4)
2‐3 days Binds T3; carrier for retinol‐ binding protein
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Serum Protein
Retinol‐ binding protein
Normal Half‐life Function Value Mean (+ SD or Range) 0.372 + 12 Transports vitamin A in 0.0073 hours plasma; binds noncovalently to prealbumin 61
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Serum Protein
Fibronectin
Normal Half‐life Value Mean (+ SD or Range) Plasma: 4‐24 2 92+0 2 2.92+0.2 h hours Serum: 1.82+0.16
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Serum Protein
Insulin‐like gro th growth factor‐1 (IGF‐1)
Normal Half‐life Function Value Mean (+ SD or Range) 0.83IU/mL 2‐6 One of a family of ins lin like of insulin‐like (0 55 1 4) hours (0.55‐1.4) h peptides that have anabolic actions on fat, muscle, cartilage, and cultured cells C. P. Fernandez
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Function
A glycoprotein fo nd in man found in many tissues; a soluble form appears in blood; involved in wound healing 63
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