Nutrition Assessment: Biochemical Assessment Flashcards
What are features of the biochemical analysis
- Can detect sub-clinical deficiences before signs/ symptoms appear
- usually measured by blood and urine samples as they are easily affected by acute changes
- Pt results compared to reference values which may differ with with different labs
How does biochemical analysis differ from dietary assessment?
- biochemical or lab values tell you if a individual has a deficiency
- dietary assessment tells you about risk for deficiency
What are some common labs done in biochemical analysis?
- CBC (complete blood cell count) - most common standard blood work (can tell if you have infection)
- Hgb
- serum iron
- TIBC
- Albumin
- prealbumin
- blood clotting (INR → international normalized ratio of prothrombin time)
- liver function (AST aspartate aminotransferase, ALT Alanine transaminase)
- Kidney function (BUN or blood urea nitrogen, creatinine)
- Ca2+, PO4-, Mg2+
- Lytes (Na+, K+, Cl-, CO2)
- Serum lipids
- Glucose
- Hb A1C (glycolated hemoglobin)
- CRP (C-reactive protein)
Normal ranges are provided on the test and assignments, but you will need to interpret abnormal/normal values
What lab tests are used for protein status?
- blood analysis through serum proteins which is not ideal but still best option → serum albumin & thyroxin binding protein (prealbumin)
- Nitrogen balance
- creatinine excretion
Why are serum proteins not ideal for protein status?
- not always representative of protein status
- low sensitivity, low specificity
- affected by many factors
Best option though so still used
What factors affect serum proteins?
- protein intake
- protein metabolism/synthesis
- hydration
- medications
- medical condition
- activity level
- pregnancy
Features of serum albumin
Half-life of 20 days so it is a better marker of chronic malnutrition, (long-term protein status) and is insensitive to acute nutritional change
* ↓ significantly with overhydration (more fluid on board)
* ↓ significantly with acute illness; influenced by presence of renal or liver disease
When is serum albumin measures most useful?
- Pts being followed long term
- Pts with NO acute illness
Serum albumin ranges to detect protein status
detects level of visceral protein depletion without confounding variables
Features of prealbumin
Gold standard for short term changes in protein status with half-life of 2 days
* sensitive to acute nutritional changes
* ↓ significantly (severe deficit <0.5 g/L) with acute illness
When is prealbumin measures most useful?
- Pts being followed in hospital
- Once Pt is recovering
Features of nitrogen balance
A measurement that reflects total protein mass by comparing nitrogen losses to nitrogen intake
* requires a 24 hr urine collection
* urea excreted = measure of protein breakdown (nitrogen intake - nitrogen losses)
Where is nitrogen balance used?
Some specific clinical populations such as ICUs but not very accurate
* Can result in overestimate of nitrogen losses because doesn’t consider miscellaneous nitrogenous losses in skins and hair (up to 8 mg/kg/d).
Features of creatinine excretion
Reflects muscle mass and increases with muscle wasting
Where is creatinine excretion measured?
used in some specific clinical populations such as ICUs with bedridden patients
What nutrients should be checked if pt is anemic?
B12, folate and iron as they are all needed for RBC synthesis and may account for different types of anemic condition.
What are the types of anemia?
- anemia of chronic disease (which is not iron deficiency anemia)
- anemia due to dietary deficits (eg iron, B12, folate etc)
- anemia due to iron losses/malabsorption of iron (Celiac Disease, excessive menstrual losses, GI bleeds, infection like Giardia etc)
Purpose of CBC with anemic patient
differentiate between anemia of chronic diseases vs dietary intake or both
B12 and folate deficiency anemia
megaloblastic anemia → lack of vitamin B12 or folate causes the body to produce abnormally large red blood cells (but not as red) that can’t function properly
What conditions may lead to B12 and folate deficiency anemia
- chronic disorders (liver disease, kidney disease, alcoholism)
- malabsorption diseases (celiac)
- pts with short gut and missing duodenum where B12 is absorbed
- dietary → seniors, vegans
What are the stages of iron deficiency?
- stage 1 depleted stores: Storage (ferritin) = liver, bone marrow, spleen
- stage 2 early functional iron deficiency: Transport (transferrin)
- stage 3 iron deficiency anemia : Essential (Hgb) = RBC, myoglobin, enzymes
What is iron deficiency anemia considered a clinical deficiency?
Once all storage and transport iron is used up
What does low ferritin mean?
Risk goes up to develop IDA
What elements are considered when diagnosing IDA?
- RBCs (Hgb)
- ferritin
- transferrin
- saturation (Fe/TIBC)
Latter 3 are typically in renal services vs. CBC
RBCs in diagnosing IDA
- typically ↓ Hgb (gives diagnosis of anemia)
- Hematocrit (HCT); gives information about iron content in RBC; typically, but not always ↓; A low HCT: hypochromic → lighter brown, not as red
- Mean cell volume (MCV): gives information of size/volume; typically ↓. A low MCV would be a microcytic anemia → looks more shrivelled
- May have increased # of reticuloycytes (immature RBC); compensatory mechanism
- May have modestly elevated platlet counts (mild thrombocytopenia) due to high erythopoietin levels; all compensatory
Combo of HCT and MCV is common
ferritin in diagnosis of IDA
Typically low and is very sensitive of iron depletion in body; but may be difficult to assess if patient has chronic inflammation where values may be elevated (even in presence of iron deficiency anemia).
* Ferritin may be elevated in patients with Inflammatory Bowel Disease, Rheumatoid Arthritis, during acute and chronic infections even when patient is iron deficient!
transferrin in diagnosis of IDA
(typically high which signifies less iron in the body) is main iron transport protein. Typically levels increase in iron deficiency anemia so as to maximize the amount of iron sent to the bone marrow
serum iron/TIBC saturation
transferrin saturation is a reflection of reflection of how well free iron binds to the transferrin molecule and how sufficient/deficient iron (free) is present. Usually ↓
* Serum iron (free) not part of the HgB in RBC which may or may not be low in iron deficiency anemia but often ↓
* TIBC: surrogate marker of transferrin levels; blood test that measures the ability of iron(free) to bind to the transferrin protein; typically ↑ in iron deficiency anemia.
Ranges for transferrin saturation
Typically females are between 15-50% and males 20-50%; may vary in pediatric populations.
* <5% is indicative of iron deficiency anemia
Top reasons for IDA
- menses
- poor intake
Common screening tool for IDA
Ferritin is often used as the screening tool to screen for IDA, particularly in young females but consider other clinical info
* asking about menstrual losses in females, dietary intake, reason for other sources of blood losses (e.g presence of chronic disease).
* Consider the sources of heme and non-heme iron.
Describe CRP
C-reactive protein → A marker of acute inflammation and infection that is highly sensitive, individual and nonspecific
* cancer, CVD, TB, pneumonia, Inflammatory Bowel Disease, undiagnosed Celiac
* ICU patients: recent surgery, trauma, respiratory, renal, and coagulation failures
Where is CRP tests useful?
More useful for determining disease progress and effectiveness of treatments
* positively associated with mortality rates
* if high in the presence of no disease it is very important to look at
CRP ranges
- normal is about 1-2 mg/L
- cut-off is 7 mg/L with illness around 8-10 mg/L
What is BUN
Blood urea nitrogen → The concentration of nitrogen (as urea) in the serum and not in RBCs (blood)
What might high BUN be related to?
- Acute or chronic kidney disease with high creatinine and urea
- Dehydration
- Excessive protein intake (diet or amino acid infusions via parenteral nutrition)
- Meds such as corticosteroids, tetracycline (antibiotics)
- Obstruction of ureter, bladder or urethra
- After intense cardio such as ultra marathon with skeletal muscle breakdown
What
What might low BUN be related to?
- Malnutrition
- Profound liver disease (↓synthesis)
Describe creatinine
Produced in the muscle, creatinine is a spontaneous decomposition product of creatine and creatine phosphate (for ATP generation)
High creatinine may be related to…
- Impaired renal function
- Rhabdomyolysis (the destruction or degenerative of skeletal muscle tissue)
- Meds such as NSAIDs, cyclosporine (immunosuppressant)
Low creatinine may be related to…
- Decreased hepatic synthesis of creatine (precursor)
- Decreased muscle mass (e.g. elderly, amputation, malnutrition, muscle wasting)
When might a healthy person have low creatinine?
hard training such as ultra running
How many times should lab tests be done?
always need blood tests or other tests done about 2-3 times before making diagnosis
* need to look at bloodwork, nutrition, disease and put pieces together
