Lab values and ankle brachial index

Lab values

Lab values can be found at the American Physical Therapy Association (APTA) interpretation guide.

Before you treat: a markedly abnormal lab value means you hold or modify the planned activity and notify the supervising PT - adjusting the plan of care itself is outside the PTA’s scope. Common red flags include platelets below ~20,000/mm³ (bleeding risk with resistance or ambulation), INR above ~4 (bleeding risk), hemoglobin below ~8 g/dL (poor activity tolerance, possible transfusion need), a newly elevated troponin (suspected myocardial injury), and SpO2 below 88-90% during activity.

Example: a post-op patient has hemoglobin 7.5 g/dL and desaturates to 87% while ambulating. Both values cross hold thresholds - stop the activity, document the vitals and symptoms, and notify the supervising PT before continuing.

Vital signs

• Temperature: 97℉ - 99.6℉
  • High value indicates fever
• Resting heart rate: 60-100 beats per minute
  • Below 60 indicates bradycardia
  • Above 100 indicates tachycardia
• Respiration: 12-20 breaths per minute
  • Below 12 indicates bradypnea
  • Above 20 indicates tachypnea
• Blood pressure: less than 120/80 mmHg is normal
  • See Hypertension for the categories above normal, and “Measuring blood pressure” below for technique
• Oxygen saturation (O2 sats) 95%-100% is normal
  • Below 90% indicates possible need for supplemental oxygen

Measuring blood pressure

A reading is accurate, and comparable from one session to the next, only when the technique is standardized:

• Patient: seated with the back supported, feet flat on the floor, and legs uncrossed, after about 5 minutes of quiet rest; no talking during the reading
• Arm: bare and supported at heart level, palm up
  • An arm below heart level or left unsupported reads falsely high; an arm above heart level reads falsely low
• Cuff: the correct size (the bladder wraps 75-100% of the arm), on bare skin, with its lower edge about 1 inch (2-3 cm) above the elbow crease and the bladder over the brachial artery
  • A cuff that is too small reads falsely high, and a cuff over clothing gives an inaccurate reading
• Manual technique:
  1. Palpate the radial pulse while inflating and note the pressure at which it disappears; this estimates the systolic pressure
  2. Inflate 20-30 mmHg above that point, then deflate slowly, about 2 mmHg per second, while listening over the brachial artery with the stethoscope
  3. The first Korotkoff sound is the systolic pressure, and the point where the sounds disappear is the diastolic pressure
• A reading taken by watching the gauge alone, without auscultation or palpation, is not valid

Hematological - complete blood count

Blood is made of plasma, the liquid in which the cells float, plus red blood cells (which carry oxygen using hemoglobin), white blood cells (which defend against infection) and platelets (which help stop bleeding).

• Hemoglobin: responsible for transporting oxygen via red blood cells
  • Male: 14-18
  • Female: 12-16
    • Below normal values indicate anemia, which increases the risk for blood transfusion
    • An above normal value indicates polycythemia, which increases the risk for clogging of capillaries

Definitions

Anemia

Due to low red cell blood count, the individual presents with fatigue, pallor, shortness of breath, weakness, and lightheadedness, especially during exertion

Polycythemia

Excessive red blood cells, which lead to increased volume and thickness of the blood; symptoms include headache, dizziness, nose bleeds, vision changes, and red skin

Both conditions can cause dizziness and fatigue on exertion, but the distinguishing signs run opposite directions: anemia’s hallmark is pallor from too few red cells, while polycythemia’s hallmark is ruddy, red skin from too many.

• Hematocrit: ratio of red blood cells to total volume of blood
  • Male: 42%-52%
  • Female: 37%-47%
    • Below normal values indicate anemia, which increases the risk for blood transfusion or need for fluids
    • An above normal value indicates polycythemia, which increases the risk for clogging of capillaries
• Platelets: clot-forming components of blood
  • 150,000-400,000/mm³
    • Below 150,000/mm³ indicates thrombocytopenia, which increases risk for hemorrhage, bleeding from gums, heavy menstrual bleeding, or blood in urine or stools
    • Above 400,000/mm³ indicates thrombocytosis, which increases risk for DVT development
• White blood count: important in immune response to infectious processes
  • 5,000-10,000/mm³
    • Below 5,000/mm³ indicates leukopenia, which increases the risk for recurrent infections
    • Above 10,000/mm³ indicates leukocytosis, which suggests infection, inflammation, or bone marrow disease (e.g., leukemia)
• Red blood count: cells that carry oxygen from the lungs to the tissue and are produced within the bone marrow
  • Male: 4.7-6.1
  • Female: 4.2-5.4
    • Below normal values indicate anemia, which increases the risk for blood transfusion
    • An above normal value indicates polycythemia, which increases the risk for myocardial infarction and stroke
• INR (international normalized ratio): the specific blood test used to measure the time it takes for blood to form a blood clot
  • 0.8-1.2: normal range for a person not on anticoagulants
  • For most patients on warfarin, the therapeutic target is 2.0-3.0; some indications use a different range (for example, 2.5-3.5 for some mechanical heart valves), so check the patient’s own target
    • Below 2.0: sub-therapeutic - blood may clot too easily, increasing the risk of thrombosis, stroke, or embolism
    • Above 3.0: supra-therapeutic - blood is too thin, increasing the risk of bleeding, with that risk rising notably above ~3.5, especially dangerous in falls or with trauma

Liver panel

• Albumin: A protein that assists with moving small molecules such as bilirubin, progesterone, and calcium through the body
  • 3.5-5.0 g/dL
    • Lab value that indicates nutritional status in the last 12-18 days
    • Below 3.5 indicates malnutrition
      • Will need to increase overall protein intake
    • Above 5.0 most often reflects dehydration/hemoconcentration rather than a nutritional or renal problem (true hyperalbuminemia is rare)
• Pre-albumin: a short-lived protein that carries thyroid hormone and vitamin A (retinol) in the blood.
  • 15-36
    • Reflects nutritional status over the past 2-3 days (short half-life)
      • This is the preferred lab value for nutritional status
    • Below 15 indicates malnutrition
      • Will need to increase overall protein intake
    • Above 36 may indicate chronic kidney disease (reduced renal clearance), corticosteroid use, or dehydration

Renal function

• Blood urea nitrogen (BUN): Measures the metabolic function of the liver (which makes urea) and the excretory function of the kidney
  • 10-20
    • Below 10 indicates liver disease, malnutrition, or overhydration
    • Above 20 indicates dehydration, kidney disease or failure, GI bleeding, a high-protein diet, extensive burns, or sepsis
• Creatinine: Elevated levels suggest impaired kidney filtration
  • Normal ~0.6-1.3 mg/dL
    • Above normal renal disease, rhabdomyolysis, endocrine dysfunction

Definitions

Rhabdomyolysis

Rapid breakdown of skeletal muscle that releases its cell contents (myoglobin, creatine kinase, and potassium) into the bloodstream; myoglobin can damage the kidneys, raising creatinine.

Cardiac lab values

• Troponin:
  • Lab value indicates suspected acute coronary ischemic disease
    • Troponin T: < 0.1
    • Troponin I: < 0.03
      • Above normal: myocardial injury or myocardial infarction
• B-type natriuretic peptide (BNP): released by the ventricles when volume or pressure overload stretches them
  • Normal: < 100 pg/mL
    • Above normal: supports a heart failure assessment, read alongside the clinical picture; kidney disease, older age, and other heart and lung conditions can also raise it

Electrolytes

• Potassium (K+): essential for heart rhythm and muscle contraction
  • 3.5-5.0 mEq/L
    • Below 3.5 (hypokalemia): muscle weakness, cramps, fatigue, and arrhythmias
    • Above 5.0 (hyperkalemia): muscle weakness and dangerous arrhythmias
    • Report either finding to the supervising PT before exercise

Arterial blood gases

How to interpret these values is covered in Understanding arterial blood gases.

• pH: 7.35-7.45
• Partial pressure of carbon dioxide (PaCO₂): 35-45 mmHg
• Bicarbonate (HCO₃): 22-26

Lipid panel

• Low density lipoprotein (LDL - bad cholesterol):
  • Creates plaque and occlusions in blood vessels
  • Normal <100
    • Low levels can result from hypoproteinemia (malabsorption, malnutrition, or severe burns) or hyperthyroidism
    • High levels increase the risk for cardiovascular disease; causes include familial hypercholesterolemia, hypothyroidism, liver or kidney disease, and a diet high in cholesterol, saturated fat, and alcohol
• High density lipoprotein (HDL - good cholesterol):
  • Helps to remove excess cholesterol deposits
  • Normal: >60 mg/dL
  • Below 40 mg/dL (men) or below 50 mg/dL (women) indicates increased risk for cardiovascular disease
• Triglycerides:
  • Produced in the liver and transported to fatty tissue
  • Desirable <150
    • Above 150 is hypertriglyceridemia, which increases the risk for cardiovascular disease; causes include hypothyroidism and a diet high in carbohydrates or alcohol
    • No specific value - hypotriglyceridemia indicates increased risk for malnutrition
• Total cholesterol:
  • Main lipid associated with cardiovascular disease
    • <200
      • 200 or higher hypercholesterolemia indicates increased risk for cardiovascular disease
      • No specific value - hypocholesterolemia indicates increased risk for malnutrition
• Statins (cholesterol-lowering drugs) can injure the liver; patients should report jaundice, dark urine, or unusual weakness or fatigue, which can prompt liver function tests (AST, ALT). Statins may also raise the risk of type 2 diabetes, mainly in people who already have an elevated diabetes risk, such as those with excess weight, prediabetes or metabolic syndrome.

Ankle brachial index (ABI)

The ABI screens for peripheral arterial disease by comparing systolic blood pressure at the ankle to systolic blood pressure at the arm. With the patient supine and resting, a Doppler probe measures the systolic pressure in the brachial artery of each arm and in the dorsalis pedis and posterior tibialis arteries of each ankle. The ABI for a leg is the higher of that leg’s two ankle pressures divided by the higher of the two brachial pressures.

$$\text{ABI}=\frac{\text{higher ankle pressure (DP or PT)}}{\text{higher brachial pressure}}$$

Example: Calculating ABI

A patient’s highest ankle pressure is 90 mmHg and highest brachial pressure is 120 mmHg.

$$\text{ABI}=\frac{90}{120}=0.75$$

Answer: 0.75 indicates mild to moderate arterial insufficiency.

Exertional monitoring tools like the 6-minute walk test, Borg rating of perceived exertion, and normal versus abnormal blood pressure and heart rate responses to exercise are covered next, in Cardiac exercise testing.