3.2 Chemistry & Hematology Labs
Key Takeaways
- Typical adult teaching ranges (assays vary): creatinine 0.6–1.3 mg/dL, BUN 7–20 mg/dL, potassium 3.5–5.0 mEq/L; use these to flag contrast, arrhythmia, and delay-or-proceed decisions.
- Reduced eGFR raises contrast-induced nephropathy risk; hydrate, minimize contrast, consider iso-osmolar contrast, and delay truly elective PCI when creatinine is significantly elevated.
- Hypokalemia predisposes to ventricular ectopy; hyperkalemia produces peaked T waves and can progress to a sine-wave rhythm—correct potassium before elective work.
- Troponin marks myocardial injury with a rise-or-fall pattern, but it does not by itself stop a STEMI activation.
- Anemia plus dual antiplatelet therapy plus access-site bleeding is a cumulative risk; platelets below about 50–80 × 10³/µL often delay elective PCI, and a HIT history changes the heparin plan.
Chemistry & Hematology Labs
ARRT CI Patient Care B.8.a and B.8.b are not a phlebotomy hobby. The numbers on the pre-procedure sheet tell you whether contrast is reasonably safe, whether the ventricle is likely to ectopy, whether an access-site bleed will be survivable, and whether the case in front of you is a ST-elevation myocardial infarction (STEMI) that proceeds regardless of a pending enzyme. Learn typical adult teaching ranges, then learn the decision. Assays and units vary by laboratory; never treat a textbook interval as a hidden ARRT cutoff.
Quick Answer: Creatinine 0.6–1.3 mg/dL and blood urea nitrogen (BUN) 7–20 mg/dL flag kidney risk before contrast. Potassium 3.5–5.0 mEq/L flags arrhythmia risk. Troponin documents injury but does not cancel a STEMI. Low hemoglobin plus dual antiplatelet therapy plus a large sheath is a bleed waiting to happen. Platelets below about 50–80 × 10³/µL often delay elective PCI.
Chemistry (B.8.a)
Creatinine, BUN, and contrast-induced nephropathy
Typical adult teaching range for serum creatinine is about 0.6–1.3 mg/dL. Typical BUN is about 7–20 mg/dL. Creatinine is the better single snapshot of filtration; BUN also moves with volume status, gastrointestinal bleed, and high protein load. What the cath lab actually uses is estimated glomerular filtration rate (eGFR) derived from creatinine (and demographics). When eGFR is reduced, contrast-induced nephropathy (CIN) risk rises. There is no single magic creatinine that ARRT publishes as a stop number. The operational pattern is:
- Hydrate when the clinical picture allows—isotonic saline is the usual preventive measure, started before contrast when the case is not a true emergency.
- Minimize contrast volume and avoid left ventriculography you do not need.
- Consider iso-osmolar contrast (for example iodixanol) in higher-risk kidneys; this is operator and protocol driven, not a substitute for hydration.
- Delay truly elective PCI when creatinine is significantly elevated and the indication can wait. A creatinine of 2.1 mg/dL on an elective day is a reason to pause, hydrate, restage, or choose a contrast-sparing strategy—not a reason to pretreat and hope.
- Hold metformin around the contrast exposure when kidney function is reduced, because superimposed CIN plus metformin is the lactic-acidosis pathway. That hold is a medication safety step tied to the creatinine, not a separate outline leaf.
Trap: A normal BUN with a rising creatinine is still kidney trouble. A high BUN with a normal creatinine in a dry patient is volume, not a free pass to unload 250 mL of contrast.
Electrolytes — potassium first
Typical adult potassium is 3.5–5.0 mEq/L. This is the electrolyte that changes the case in front of you.
- Hypokalemia (for example 2.8 mEq/L after diuretics) predisposes to ventricular ectopy, pause-dependent ventricular tachycardia, and digoxin-related arrhythmias. On an elective table, correct it before you instrument the heart. Ischemia plus a low potassium is how a diagnostic catheter becomes a resuscitation.
- Hyperkalemia produces peaked T waves, PR prolongation, QRS widening, and, at the extreme, a sine-wave rhythm. An elective PCI does not start with a potassium of 6.4 mEq/L. Treat, recheck, then talk about wires.
Sodium, magnesium, and calcium matter, but potassium is the CI-exam decision value. If the tracing suddenly looks peaked after a long case with hemolyzed samples or succinylcholine in a crash induction, think potassium before you think a new lead placement error.
Glucose
Typical fasting teaching range is about 70–99 mg/dL; random values run higher after a meal. Two cath-lab facts:
- Hyperglycemia in acute coronary syndrome (ACS) is associated with worse outcomes. You are not the physician writing an insulin drip, but you should not ignore a glucose of 340 mg/dL on the pre-op sheet as irrelevant chemistry.
- Hypoglycemia under sedation is an emergency. A diaphoretic, confused patient with a glucose of 42 mg/dL is not oversedated until you have a number. Treat hypoglycemia; do not deepen sedation to stop the restlessness.
NPO status makes hypoglycemia more likely in insulin-treated patients. Have a point-of-care glucose in the room, not in another department.
Cardiac enzymes — troponin
Troponin (high-sensitivity troponin I or T, depending on the lab) is the marker of myocardial injury. A rising or falling pattern distinguishes acute injury from a chronically elevated baseline in kidney disease or heart failure. Important CI distinction: troponin does not by itself stop a STEMI activation. STEMI is an electrocardiogram and clinical diagnosis. You do not hold the emergency PCI because the first troponin is still pending or still within the 99th percentile. Conversely, a rising troponin in a patient without ST elevation is non–ST-elevation ACS timing, not a reason to skip antiplatelet and anticoagulation planning.
Older enzyme names (CK-MB, total CK) still appear on some outlines and old reports. For current practice, troponin is the decision enzyme.
Hematology (B.8.b)
Hemoglobin and hematocrit
Typical adult hemoglobin teaching ranges are about 12–16 g/dL in women and 13.5–17.5 g/dL in men. Hematocrit is roughly three times the hemoglobin (about 36–46% and 41–53%). Anemia plus dual antiplatelet therapy plus an arterial sheath is cumulative bleeding risk, not three separate problems. Large-bore femoral access, chronic kidney disease, and glycoprotein IIb/IIIa inhibitors stack on top.
Transfusion thresholds are physician-driven. Do not memorize a fake ARRT hemoglobin at which you must transfuse. What you must do is recognize that a hemoglobin of 7.2 g/dL before elective femoral PCI is a conversation, a possible delay, and a reason to be obsessive about access-site hemostasis. During the case, a falling hematocrit with groin fullness is a bleed until proven otherwise.
Platelet count and HIT
Typical platelet count is about 150–400 × 10³/µL. Counts below about 50–80 × 10³/µL often delay elective PCI because you cannot safely combine arterial puncture with dual antiplatelet therapy. Emergency primary PCI is a different risk conversation, but it is still not a free pass to ignore a platelet count of 18 × 10³/µL.
Heparin-induced thrombocytopenia (HIT) is a history question, not just a number. A falling platelet count after recent heparin, or a documented HIT antibody, changes the anticoagulation plan: unfractionated heparin is the problem, and the operator will reach for a non-heparin agent (commonly bivalirudin or argatroban) rather than a heparin bolus into the sheath. Flag the history before the bolus, not after the ACT comes back.
White blood cell count
Typical white blood cell (WBC) count is about 4.5–11.0 × 10³/µL. Elevation has two common cath-lab stories:
- Infection — fever, a hot groin from a prior stick, or a planned implant (pacer, closure device) should make a high WBC a pause for elective work.
- Stress leukocytosis — ACS, catecholamines, and steroids raise the WBC without an abscess. Do not diagnose pneumonia from a WBC of 14 × 10³/µL on a STEMI sheet, and do not ignore 22 × 10³/µL plus fever on an elective day.
Lab value table — typical teaching ranges and why the CI exam cares
Ranges below are typical adult teaching intervals. Your lab's reference, the patient's sex and muscle mass, and the assay all move the numbers.
| Value | Typical teaching range | Why the CI exam cares |
|---|---|---|
| Creatinine | 0.6–1.3 mg/dL | CIN risk; contrast volume; hydration; delay elective work when substantially elevated |
| BUN | 7–20 mg/dL | Renal perfusion and volume status alongside creatinine |
| Potassium | 3.5–5.0 mEq/L | Hypokalemia → ventricular ectopy; hyperkalemia → peaked T, sine wave; correct before elective PCI |
| Glucose | Fasting ~70–99 mg/dL | Hyperglycemia worsens ACS outcomes; hypoglycemia under sedation is an emergency |
| Troponin | Assay-specific 99th percentile | Myocardial injury with rise/fall; does not cancel STEMI activation |
| Hemoglobin | ~12–16 g/dL (F), ~13.5–17.5 g/dL (M) | Anemia + DAPT + access bleeding; transfusion is physician-driven |
| Hematocrit | ~36–46% (F), ~41–53% (M) | Tracks with hemoglobin; falling Hct after access suggests bleeding |
| Platelets | 150–400 × 10³/µL | <50–80k often delays elective PCI; HIT history changes heparin plan |
| WBC | 4.5–11.0 × 10³/µL | Infection vs stress leukocytosis; elective implants and groins care about fever plus high WBC |
Scenario — creatinine 2.1 mg/dL before elective PCI
A 74-year-old with stable angina is on the table for elective single-vessel PCI. Pre-op labs: creatinine 2.1 mg/dL, BUN 32 mg/dL, potassium 4.1 mEq/L, hemoglobin 13.0 g/dL, platelets 220 × 10³/µL, troponin negative. This is not a STEMI. The kidney, not the coronary, is the reason to slow down.
Team actions that match B.8.a: notify the operator before the first contrast injection; hydrate if volume status allows; minimize contrast (skip a non-essential ventriculogram, collimate, use dilute contrast for puffs); discuss iso-osmolar contrast; consider staging the PCI rather than ad hoc multi-vessel work; hold metformin if the patient takes it. What you do not do is treat 2.1 mg/dL as a normal variant because the patient feels fine, and you do not reverse a STEMI activation if this same creatinine appears on a primary-PCI sheet—you still protect the kidney, but you do not cancel reperfusion for an enzyme of filtration.
Exam traps
- Troponin pending is not a STEMI stop. Creatinine 2.1 mg/dL is an elective stop-and-plan.
- A hemolyzed potassium of 6.0 mEq/L may be fake; a non-hemolyzed 6.0 mEq/L with peaked T waves is real. Recheck before you treat the lab instead of the patient, but do not ignore the tracing.
- Platelet count 40 × 10³/µL is not rescued by a normal hemoglobin. They answer different bleed problems.
- WBC 13 × 10³/µL in ACS can be stress. WBC 13 × 10³/µL plus a red hot groin is infection until the operator says otherwise.
An elective PCI patient has a non-hemolyzed potassium of 2.8 mEq/L and frequent premature ventricular complexes on the table monitor. What is the appropriate lab-driven decision?
A stable patient scheduled for elective PCI has a creatinine of 2.1 mg/dL and a BUN of 32 mg/dL. Which concern should drive the next step?
An elective femoral PCI candidate has platelets of 40 × 10³/µL, hemoglobin 13.4 g/dL, and a remote history of HIT. Which statement best matches hematology decision-making?