Analyzes comprehensive metabolic panels, CBCs, lipid panels, and thyroid function with clinical correlation. Use when reviewing outpatient labs, identifying abnormalities, or correlating lab trends.
Analyzes comprehensive metabolic panels, CBCs, lipid panels, and thyroid function with clinical correlation.
Outpatient laboratory interpretation is a core primary care competency that directly drives clinical decisions: medication adjustments, specialist referrals, diagnosis of new conditions, and monitoring of chronic diseases. Approximately 70% of medical decisions are influenced by lab results, yet abnormal values frequently go un-actioned—studies show 7-8% of abnormal outpatient labs lack documented follow-up. Errors in interpretation range from misattributing hemolysis artifacts to clinical significance to missing subtle trends in renal function decline.
This skill provides a structured framework for interpreting the most commonly ordered outpatient panels (CMP, CBC, lipids, thyroid, A1c, urinalysis) with emphasis on clinical correlation, trend analysis, and appropriate next steps. It ensures that every abnormal value is either explained by a known diagnosis, flagged for workup, or documented as clinically insignificant with rationale.
| Analyte | Reference Range | Common Causes of High | Common Causes of Low | Critical Action Threshold |
|---|---|---|---|---|
| Sodium | 136-145 mEq/L | Dehydration, diabetes insipidus, excess salt | SIADH, diuretics, heart failure, cirrhosis | <120 or >160: urgent evaluation |
| Potassium | 3.5-5.0 mEq/L | ACEi/ARB, CKD, hemolysis (artifact), spironolactone | Diuretics, vomiting, diarrhea, insulin | <3.0 or >6.0: ECG, urgent correction |
| Chloride | 98-106 mEq/L | Dehydration, renal tubular acidosis | Vomiting, diuretics, metabolic alkalosis | Interpret with sodium and bicarb |
| CO2 (bicarb) | 22-29 mEq/L | Metabolic alkalosis, vomiting, diuretics | Metabolic acidosis (DKA, lactic, CKD), diarrhea | <15: urgent evaluation for acidosis |
| BUN | 7-20 mg/dL | Dehydration, GI bleed, high protein diet, CKD | Liver disease, malnutrition, overhydration | Interpret BUN:Cr ratio |
| Creatinine | 0.7-1.3 mg/dL (M); 0.6-1.1 (F) | CKD, AKI, muscle mass, dehydration, medications | Low muscle mass, amputation, malnutrition | Rise >0.3 mg/dL from baseline: evaluate AKI |
| eGFR | >60 mL/min/1.73m² | N/A | CKD staging: G3a 45-59, G3b 30-44, G4 15-29, G5 <15 | <30: nephrology referral |
| Glucose (fasting) | 70-99 mg/dL | Diabetes, prediabetes, stress, steroids | Insulin excess, oral hypoglycemics, adrenal insufficiency | >400 or <50: immediate action |
| Calcium | 8.5-10.5 mg/dL | Hyperparathyroidism, malignancy, thiazides, vitamin D excess | Hypoalbuminemia (correct), CKD, hypoparathyroidism | Correct for albumin: add 0.8 per 1g albumin below 4.0 |
| Albumin | 3.5-5.0 g/dL | Dehydration | Liver disease, nephrotic syndrome, malnutrition, inflammation | <2.0: significant malnutrition or liver failure |
| Total bilirubin | 0.1-1.2 mg/dL | Hemolysis, Gilbert syndrome, hepatitis, obstruction | Rare; not clinically significant | >3.0: evaluate direct vs. indirect; imaging if direct elevated |
| ALP | 44-147 IU/L | Bone disease, biliary obstruction, pregnancy, growth in children | Rare; zinc deficiency, hypothyroidism | Fractionate with GGT to distinguish bone vs. liver |
| AST | 10-40 IU/L | Hepatitis, alcohol, medications, MI, muscle injury | Not clinically significant | >1000: acute hepatitis workup |
| ALT | 7-56 IU/L | Hepatitis, NAFLD/NASH, medications, alcohol | Not clinically significant | ALT >3x ULN on statin: hold statin, evaluate |
| Parameter | Reference Range | Key Patterns |
|---|---|---|
| WBC | 4.5-11.0 × 10³/µL | Elevated: infection, stress, steroids, leukemia. Low: viral, medications, bone marrow suppression |
| Hemoglobin | 14-18 g/dL (M); 12-16 g/dL (F) | Anemia classification by MCV: microcytic (<80), normocytic (80-100), macrocytic (>100) |
| MCV | 80-100 fL | Low: iron deficiency, thalassemia. High: B12/folate deficiency, alcohol, hypothyroidism, MDS |
| RDW | 11.5-14.5% | Elevated: iron deficiency (early marker), mixed deficiency. Normal in thalassemia trait |
| Platelets | 150-400 × 10³/µL | High: reactive (infection, inflammation, iron deficiency), myeloproliferative. Low: ITP, medications, liver disease, DIC |
Iron deficiency anemia workup (MCV <80 + low ferritin):
Macrocytic anemia workup (MCV >100):
Apply ACC/AHA 2018 cholesterol guidelines:
| Component | Desirable | Borderline | High Risk |
|---|---|---|---|
| Total cholesterol | <200 mg/dL | 200-239 | ≥240 |
| LDL-C | <100 mg/dL (general); <70 (ASCVD) | 100-159 | ≥160; very high-risk ASCVD: <55 |
| HDL-C | ≥40 (M); ≥50 (F) | N/A | Low HDL is independent CV risk factor |
| Triglycerides | <150 mg/dL | 150-499 | ≥500: pancreatitis risk; initiate fibrate or omega-3 |
| Non-HDL-C | <130 mg/dL | 130-159 | ≥160 |
Statin decision framework:
TSH interpretation:
| TSH (mIU/L) | Free T4 | Interpretation | Action |
|---|---|---|---|
| 0.4-4.0 | Normal | Euthyroid | No action |
| >4.0, <10 | Normal | Subclinical hypothyroidism | Repeat in 6-12 weeks; treat if symptomatic, pregnant, or TSH >10 |
| >10 | Low | Overt hypothyroidism | Start levothyroxine 1.6 mcg/kg/day; lower in elderly/cardiac |
| <0.4 | Normal | Subclinical hyperthyroidism | Repeat in 6-12 weeks; refer endocrinology if persistent |
| <0.1 | High | Overt hyperthyroidism | Urgent endocrinology referral; check T3, TSI/TRAb |
A1c interpretation:
For each abnormal value:
Document each disposition with rationale and timeline for follow-up.