8.2 Laboratory Values

Reading Labs for Risk

Laboratory values let the LPN/VN detect problems before symptoms appear. On the NCLEX-PN, the tested skill is rarely diagnosis — it is recognizing a critical value and reporting it to the RN, and understanding the consequence of acting on a dangerous result (for example, never giving potassium when the serum level is already high).

Complete Blood Count (CBC)

Clinical thresholds: an absolute neutrophil count (ANC) below 1,500 means neutropenia and high infection risk — institute neutropenic precautions; below 500 is severe. Platelets below 20,000 is critical for spontaneous bleeding; below 50,000 increases procedural bleeding. Leukocytosis (> 11,000) suggests infection; leukopenia suggests marrow suppression.

Coagulation Studies

Worked example: a patient on warfarin has an INR of 4.5. Because the target is 2.0-3.0, this is supratherapeutic — bleeding risk is high, so you hold the next dose and notify the prescriber; vitamin K may be ordered.

Basic Metabolic Panel

Critical values to memorize:

Hyperkalemia (> 6.5) causes peaked T waves and lethal arrhythmias — report immediately and expect calcium gluconate, insulin with dextrose, or kayexalate. Hypokalemia (< 3.5) potentiates digoxin toxicity. Hyponatremia causes confusion and seizures; correct sodium slowly to avoid demyelination.

Cardiac Markers

Troponin is the most specific marker for myocardial infarction. BNP above 100 pg/mL points to heart failure and helps distinguish cardiac from pulmonary dyspnea.

Liver, Renal, and Thyroid Snapshots

ALT is the most liver-specific enzyme; AST also rises with cardiac/skeletal injury. Albumin (3.5-5.0 g/dL) reflects nutrition and liver synthesis. For thyroid: high TSH with low free T4 = hypothyroid; low TSH with high T4 = hyperthyroid.

Arterial Blood Gas (ABG) Logic

Step through it: (1) pH — below 7.35 is acidosis, above 7.45 alkalosis. (2) CO2 — if it moves opposite to pH, the disorder is respiratory. (3) HCO3 — if it moves with pH, it is metabolic. (4) If pH is back in range, it is compensated. Example: pH 7.28, CO2 52, HCO3 24 — low pH with high CO2 (opposite directions) = uncompensated respiratory acidosis, classic for hypoventilation or opioid sedation. A common trap is forgetting that COPD patients carry chronically high CO2 with a normal pH (compensated).

Urinalysis and Renal Reasoning

A urinalysis adds quick risk data. Normal urine specific gravity is 1.005-1.030; a high value points to dehydration, a low value to overhydration or impaired concentrating ability. Glucose or ketones in the urine suggest uncontrolled diabetes, protein suggests glomerular damage, and nitrites with leukocyte esterase suggest a urinary tract infection. Pair the BUN-to-creatinine picture with this: a BUN that rises out of proportion to creatinine usually means dehydration, whereas both rising together points to intrinsic kidney injury. The LPN/VN reports these patterns so the RN and provider can adjust fluids and nephrotoxic drugs.

Reporting and Critical-Value Workflow

Facilities maintain a critical-value list, and labs phone these results directly to a licensed nurse. The LPN/VN's role is to receive or relay that result, perform a read-back to confirm accuracy, notify the RN and provider promptly, document the time and content of the call, and monitor the patient for related signs. For example, a hemoglobin of 6.5 g/dL means symptomatic anemia and possible transfusion — assess for fatigue, pallor, and tachycardia while reporting.

The tested judgment is consistent across labs: identify the dangerous value, connect it to the patient's clinical picture, and escalate rather than simply charting the number.