lab values

Lab values must always be interpreted based on what 3 major factors?

Reference range, trends over time, clinical context 

What is a critical lab value?

Value far outside normal that poses immediate health risk and requires provider action 

What patient factors can alter “normal” lab values?

Age, race/ethnicity, sex, gender 

How should lab values be interpreted in transgender patients on hormone therapy?

Use affirmed gender (except troponin & PSA) 

What determines how lab values are interpreted?

The specific lab + patient context (ranges vary by facility) 

Why are lab trends more important than single values?

Show progression (improving vs worsening condition)

What are the 2 major components of blood?

Formed elements + plasma 

What are formed elements?

RBCs, WBCs, platelets 

What is plasma?

Fluid containing proteins, nutrients, waste, ions 

Normal WBC range

5,000–10,000/mm³ 

Primary function of WBCs

Fight infection 

What WBC fights bacterial infection?

Neutrophils

What WBC is elevated in allergies/parasites?

Eosinophils

What WBC is involved in allergic/myeloproliferative disorders?

Basophils

What WBC fights viral infections?

Lymphocytes

What WBC performs phagocytosis?

Monocytes

What is leukocytosis?

WBC >11,000 (infection, inflammation, trauma, leukemia) 

Critical leukocytosis value

30,000

What is leukopenia?

WBC <4,000 (infection risk) 

Critical leukopenia value

What is neutropenia?

Low neutrophils → ↑ infection risk (ANC <1,000) 

A patient has WBC = 18,000 and fever. PT decision?

Likely infection → monitor vitals, modify intensity, consider holding if unstable

A patient has WBC = 2,000. What is priority?

Infection prevention (neutropenic precautions)

Why avoid crowded areas with low WBC?

High infection risk

What are neutropenic precautions?

Isolation, PPE, no shared items, avoid flowers/fruit 

PT modification with WBC abnormalities

Monitor fatigue, adjust intensity/duration 

Normal RBC count (male)

4.7–6.1 million/mm³ 

Normal RBC count (female)

4.2–5.4 million/mm³ 

Primary function of RBCs

Carry oxygen 

RBC lifespan

~120 days 

What is hematocrit?

% of blood made of RBCs 

Normal HCT (male)

42–52% 

Normal HCT (female)

37–47% 

What is hemoglobin?

Oxygen-carrying protein in RBCs 

Normal Hb (male)

14–18 g/dL 

Normal Hb (female)

12–16 g/dL 

What is anemia?

↓ RBC, Hb, HCT → ↓ oxygen delivery 

Common cause of anemia in US

Chronic blood loss (iron deficiency) 

What is polycythemia?

↑ RBC, Hb, HCT (often from chronic hypoxia) 

Critical HCT values

Critical Hb values

A patient has Hb = 6. PT action?

Likely hold or very light activity, consult team (transfusion possible)

Why is SpO₂ misleading in anemia?

Oxygen saturation normal but total O₂ content low 

A patient fatigues quickly with normal vitals but low Hb. Why?

Poor oxygen delivery to tissues

Normal platelets

150,000–400,000/mm³ 

Platelet function

Blood clotting 

Critical platelet values

What is thrombocytopenia?

Low platelets → bleeding risk 

What is thrombocytosis?

High platelets → clot risk 

Signs of thrombocytopenia

Petechiae, purpura, ecchymosis 

PT considerations with low platelets

Fall prevention, avoid trauma, monitor bleeding 

Patient platelets = 40,000. PT decision?

Avoid high-risk activity, falls → modify or hold

Why avoid dry needling with low platelets?

Increased bleeding risk

Normal PT (lab)

11–12.5 sec 

Normal PTT

30–40 sec 

Normal INR

0.8–1.2 

Critical PTT

70 sec 

Critical PT

~20 sec 

Critical INR

5.5 

Why are PT/PTT/INR monitored?

Anticoagulation therapy (bleeding risk) 

Patient INR = 6. PT action?

Hold or very cautious → high bleeding risk

What should PT monitor with high INR?

Bruising, bleeding, neuro changes

What intervention if bleeding occurs?

Apply prolonged pressure 

Normal sodium (Na⁺)

136–145 mmol/L 

Normal potassium (K⁺)

3.5–5.0 mmol/L 

Normal chloride (Cl⁻)

98–106 mmol/L 

Normal bicarbonate (HCO₃⁻)

22–26 mEq 

Normal BUN

10–20 mg/dL 

Normal creatinine

M: 0.6–1.2, F: 0.5–1.1 mg/dL 

Normal glucose

74–106 mg/dL 

Critical glucose values

Patient glucose = 65 before PT. Action?

Give 15–30g carbs before activity 

Patient glucose = 300. PT concern?

Check ketones → risk of ketoacidosis 

Why electrolytes matter in PT?

Affect muscle contraction, cardiac function, cognition 

Why lab values alone don’t dictate PT?

Must consider full clinical picture 

Biggest PT mistake with labs

“Getting hypnotized by numbers” instead of assessing patient 

What should you do if unsure about lab safety?

Ask nursing/interprofessional team 

What ultimately determines PT safety?

Patient presentation + hospital protocols