Lab Values Lecture

What are the five primary reasons for ordering laboratory tests according to the lecture?

Diagnosis (rule in or rule out), evaluating organ function, monitoring response to therapy, screening, and research.

How is a 'normal' laboratory range statistically defined on a standard distribution curve?

A normal range is defined as within $2$ standard deviations ($SD$) from the mean, encompassing approximately $95\%$ of the healthy population and leaving $5\%$ ($2.5\%$ on each side) categorized as abnormal.

T/F: Absolute value is more important than the trend

False : Need to consider the clinical context and trends

In laboratory testing, what is meant by high sensitivity versus high specificity?

Higher sensitivity provides confidence that a negative result is true (think ppl who are sensitive have a negative reaction), whereas higher specificity provides confidence that a positive result is true. You can not use them interchangeably.

What does each letter in the L-A-B-S acronym represent when systematically reviewing laboratory values?

L stands for Look (value and reference range); A stands for Assess the trend (previous values and rate of change); B stands for Build the clinical picture (signs, symptoms, diagnoses); S stands for Scrutinize medications (causes, safety, dose adjustments, monitoring).

What is included in a Basic Metabolic Panel (BMP)

Electrolytes (Sodium, Potassium, Chloride, Carbon Dioxide) Renal Function ( Blood, Urea, Nitrogen, Creatinine) and Metabolic (Glucose, Calcium)

Sodium Range

135-145 mEq/L

What severe clinical complications can result from extreme abnormalities in sodium levels?

Extreme hyponatremia or hypernatremia can cause seizures, coma, and death; chronic sodium abnormalities must be corrected slowly.

What is the clinical difference between azotemia and uremia?

Azotemia refers to an elevated Blood Urea Nitrogen (BUN) level without symptoms, while uremia refers to an elevated BUN level accompanied by clinical symptoms.

Which additional laboratory markers differentiate a Comprehensive Metabolic Panel (CMP) from a Basic Metabolic Panel (BMP)?

A CMP includes the 8 BMP components plus 6 additional markers: Albumin, Total Protein, Total Bilirubin, Alkaline Phosphatase (ALP), Aspartate Aminotransferase (AST), and Alanine Aminotransferase (ALT).

Which laboratory tests are most specific for assessing drug-related hepatocellular liver injury?

Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT).

What clinical parameters are evaluated to assess the loss of synthetic liver function in end-stage liver disease (cirrhosis)?

Bilirubin, INR, Serum Creatinine ($SCr$), and Sodium ($Na^+$).

What are the normal reference ranges for Phosphorus and Magnesium?

Phosphorus: $2.6\text{--}4.5\,\text{mg/dL}$; Magnesium: $1.5\text{--}2.2\,\text{mg/dL}$.

Why is magnesium repletion necessary when correcting low potassium levels?

Magnesium is essential for proper potassium balance in the body; therefore, magnesium must be repleted alongside potassium.

What are the normal adult reference ranges for White Blood Cells (WBC), Hemoglobin (Hgb), Hematocrit (Hct), and Platelets in a Complete Blood Count (CBC)?

WBC: $4\text{--}10\,\text{K/mm}^3$ ; Hgb Males: $14\text{--}18\,\text{g/dL}$, Hgb Females: $13\text{--}16\,\text{g/dL}$; Hct Males: $40\text{--}54\%$; Hct Females: $38\text{--}48\%$; Platelets: $120\text{--}400\,\text{K/mm}^3$.

What Absolute Neutrophil Count (ANC) threshold defines neutropenia?

An Absolute Neutrophil Count ($ANC$) of < 1500 indicates neutropenia.

How does Mean Corpuscular Volume (MCV) help classify different types of anemia?

Normal MCV is $80\text{--}100\,\text{fL}$. Low MCV (< 80\,\text{fL}) indicates iron deficiency anemia or anemia of chronic disease. High MCV (> 100\,\text{fL}) indicates folate or Vitamin B12 deficiency. Normal MCV indicates acute blood loss, chronic disease, or bone marrow failure.

What is the primary laboratory test used to monitor anticoagulation therapy with Warfarin, and what is its standard therapeutic goal?

International Normalized Ratio (INR), with a standard therapeutic target of $2\text{--}3$ in most patients (baseline normal is $1$).

In acute illness, what ferritin level threshold indicates iron deficiency?

In acute illness, a ferritin level < 100\,\text{ng/mL} indicates iron deficiency (normal baseline ferritin is $20\text{--}300\,\text{ng/mL}$).

What do nitrites, leukocytes, and muddy brown tubular casts in a urinalysis (UA) indicate?

Nitrites indicate bacterial presence; leukocytes (pyuria) indicate urinary tract infection; muddy brown tubular casts indicate kidney damage.

What are the Hemoglobin A1c percentage thresholds for normal, prediabetes, and diabetes diagnosis?

Normal: < 5.7\% ; Prediabetes: $5.7\text{--}6.4\%$; Diabetes: > 6.4\%.

What are the normal reference ranges for TSH, Thyroxine (T4), and Triiodothyronine (T3)?

TSH: $0.5\text{--}4.5\,\text{mIU/L}$; Thyroxine (T4): $0.7\text{--}0.9\,\text{ng/dL}$; Triiodothyronine (T3): $2\text{--}4.4\,\text{pg/mL}$.

What is the recommended timing for drawing a serum cortisol sample, and what do abnormal values indicate?

Cortisol should be drawn early in the morning (~$0700$) during peak waking levels. Values > 15\,\text{mcg/dL} are normal, low levels indicate adrenal insufficiency, and elevated levels suggest Cushing's syndrome.

What percentage of values fall within ±1 SD of the mean?

68%

What percentage of values fall within ±2 SD of the mean?

95%

What percentage of values fall within ±3 SD of the mean?

99.7%

Accuracy vs Precision

Accuracy is the extent to which the mean measurement is close to the true value vs Precision is consistency (it can be reproduced)

Potassium Range

3.5-5.0 mEq/L

Chloride Range

95-105 mEq/L

Carbon Dioxide / Bicarbonate Range

22-26 mEq/L

Anion Gap (calculated) Range

<12 mEq/L

B-U-N Range

8-20 mg/dL

Creatinine Range

0..5-1.0 mg/dL

Glucose Range

60-100 mg/dL

Calcium Range

8.4-10.2 mg/dL

T/F: High potassium levels do not cause fatal arrhythmias

False

Blood Urine Nitrogen levels are impacted by _______ and why?

Kidneys + liver - because the liver makes urea, and kidneys eliminate urea

B-U-N is the product of _____________

Protein Metabolism

Serum Creatinine + B-U-N are both considered what?

Waste

Serum Creatinine is the primary marker of ________ function and why?

Renal because kidneys filter SCr out of the blood, so when kidney filtration decreases causing SCr to increase

When is SCr elevated

During dehydration , AKI, and CKD