Lipid Panel: Beyond Total Cholesterol—Non-HDL, ApoB, Lp(a), and Secondary Causes

LDL-C is calculated, not measured. Non-HDL may be better. And nobody's checking Lp(a) yet even though they should be.

The lipid panel is ordered on nearly every adult in primary care, yet most providers look at the LDL-C, compare it to a target, and stop. The panel actually contains much more information—and the advanced markers that are increasingly recommended (non-HDL, apoB, Lp(a)) are the ones that predict cardiovascular events better than LDL alone.

The Standard Panel

• Total cholesterol: LDL + HDL + VLDL. Largely supplanted by its components for clinical decisions.
• LDL-C: Usually calculated by the Friedewald equation (TC − HDL − TG/5). Inaccurate when triglycerides >400 (equation breaks down) or when LDL is very low. Direct LDL measurement is available but not standard.
• HDL-C: Higher is generally protective. Very low HDL (<40 men, <50 women) increases cardiovascular risk. Pharmacologically raising HDL has NOT been shown to reduce events.
• Triglycerides: Fasting preferred for accuracy but non-fasting is acceptable for screening. >500 mg/dL = pancreatitis risk requiring treatment regardless of cardiovascular risk.
• Non-HDL cholesterol = Total cholesterol − HDL. Captures ALL atherogenic lipoproteins (LDL + VLDL + IDL + Lp(a)). Better predictor of cardiovascular risk than LDL-C alone, especially in patients with elevated triglycerides where calculated LDL is unreliable. Target: typically LDL goal + 30.

Advanced Markers: When to Go Beyond the Standard Panel

ApoB (Apolipoprotein B)

Each atherogenic lipoprotein particle (LDL, VLDL, IDL, Lp(a)) contains exactly one apoB molecule. ApoB therefore counts the total number of atherogenic particles, making it the single best measure of atherogenic burden. It's superior to LDL-C in patients with metabolic syndrome, diabetes, obesity, or high triglycerides where LDL-C may underestimate risk (discordance between particle number and cholesterol content). Consider ordering when LDL-C is at goal but the patient has metabolic syndrome or premature ASCVD.

Lp(a) (Lipoprotein(a))

The most underordered cardiovascular risk marker in medicine. Lp(a) is a genetically determined, highly atherogenic lipoprotein that is NOT lowered by statins, diet, or exercise. Elevated Lp(a) (>50 mg/dL or >125 nmol/L) independently increases ASCVD risk 2–3 fold and aortic stenosis risk. Current guidelines (2024 ESC, AHA/ACC consideration) recommend checking Lp(a) at least once in every adult's lifetime since it's genetically fixed. If elevated, it changes risk stratification (may warrant more aggressive LDL lowering) and will have targeted therapies (antisense oligonucleotides) entering the market.

When to Order Lp(a)

Check at least once in all adults. Especially important in: premature ASCVD (men <55, women <65), family history of premature ASCVD, recurrent events despite optimal statin therapy, borderline risk where Lp(a) could change the treatment decision, and calcific aortic stenosis.

Fasting vs. Non-Fasting

Current guidelines (2018 AHA/ACC, 2024 ESC) accept non-fasting lipid panels for initial screening. Triglycerides are the main value affected by fasting (can rise 20–30% postprandially). A fasting panel is needed when: triglycerides are >400 on non-fasting, you need accurate calculated LDL-C, or you're monitoring response to triglyceride-lowering therapy.

Secondary Causes of Dyslipidemia

Before attributing dyslipidemia to "genetics" or "diet," rule out secondary causes:

Lipid Abnormality	Secondary Causes to Consider
Elevated LDL	Hypothyroidism (check TSH!), nephrotic syndrome, obstructive liver disease, anorexia, medications (thiazides, cyclosporine, retinoids)
Elevated triglycerides	Uncontrolled diabetes/insulin resistance, alcohol, obesity, CKD, medications (steroids, beta-blockers, estrogen, retinoids, atypical antipsychotics, protease inhibitors)
Low HDL	Metabolic syndrome, smoking, sedentary lifestyle, anabolic steroids, beta-blockers, progestins
Severely elevated TG (>500)	Familial hypertriglyceridemia, uncontrolled diabetes, alcohol, medications, pregnancy

Don't Miss Hypothyroidism

Hypothyroidism is one of the most common reversible causes of elevated LDL. Always check TSH before starting a statin for new dyslipidemia. Correcting the thyroid may normalize the lipids without medication.

Pediatric Lipid Screening

• Universal screening: Non-fasting lipid panel once between ages 9–11 and again at 17–21 (NHLBI guidelines).
• Targeted screening: Children ≥2 years with family history of premature ASCVD, dyslipidemia, or risk factors (obesity, diabetes, hypertension).
• Familial hypercholesterolemia should be suspected when LDL >160 in a child or >190 in an adult. Cascade screening of family members is indicated.

Bottom Line

The lipid panel is more than LDL-C. Non-HDL is free (calculate from the standard panel) and better than LDL-C in metabolic syndrome. ApoB counts atherogenic particles directly. Lp(a) should be checked once in every adult. Always rule out secondary causes before starting a statin. And check that TSH.

Stay sharp out there.

Thyroid Function Tests: TSH, Free T4, Free T3—and When You Actually Need Each One

 

Thyroid Function Tests: TSH, Free T4, Free T3—and When You Actually Need Each One

TSH is almost always enough. Free T3 is almost never needed. And sick euthyroid syndrome fools everyone.

This post complements the thyroid antibody workup from earlier in the series. That post covered which antibody to order when you suspect autoimmune thyroid disease. This one covers the function tests—TSH, free T4, and free T3—and the interpretation patterns that trip up clinicians daily.

The Hierarchy: TSH First, Always

TSH is the single best screening test for thyroid dysfunction in outpatient primary care. The pituitary amplifies small changes in thyroid hormone levels, making TSH far more sensitive than direct hormone measurement. A normal TSH essentially rules out primary thyroid disease in an outpatient setting.

TSH	Free T4	Free T3	Interpretation
↑ High	↓ Low	—	Overt hypothyroidism. Treat with levothyroxine.
↑ High	Normal	—	Subclinical hypothyroidism. Repeat in 6–12 weeks to confirm. Treat if TSH >10, or if symptomatic + anti-TPO positive, or if pregnant/trying to conceive.
↓ Low	↑ High	—	Overt hyperthyroidism. Order TSI to confirm Graves'. Consider radioactive iodine uptake if diagnosis unclear.
↓ Low	Normal	↑ High	T3 thyrotoxicosis. One of the few times free T3 is needed. Seen in early Graves' or toxic nodule.
↓ Low	Normal	Normal	Subclinical hyperthyroidism. Repeat to confirm. Consider treatment if TSH <0.1, age >65, atrial fibrillation, or osteoporosis risk.
Normal or Low	↓ Low	—	Central hypothyroidism (pituitary or hypothalamic). TSH is inappropriately normal/low despite low T4. Rare but missed if you only check TSH.
Variable	Variable	—	Sick euthyroid syndrome (nonthyroidal illness). See below.

When to Order Free T3 (Almost Never)

Free T3 is overordered in primary care. The only validated indications:

• Suppressed TSH + normal free T4: Check free T3 to detect T3 thyrotoxicosis
• Monitoring amiodarone-induced thyroid disease (complex T3/T4 dynamics)
• Suspected T3 thyrotoxicosis (early Graves', toxic adenoma)

Free T3 should NOT be ordered for: hypothyroidism monitoring (it's the last to fall and the most variable), fatigue workup, or routine screening. Treat hypothyroidism by normalizing TSH, not by chasing T3 levels.

Sick Euthyroid Syndrome (Nonthyroidal Illness)

Acutely ill hospitalized patients frequently have abnormal thyroid function tests despite having no thyroid disease. The classic pattern: low T3, low or normal T4, low/normal/slightly elevated TSH. This is an adaptive response to illness, not hypothyroidism.

The Rule

Do not check thyroid function tests in acutely ill hospitalized patients unless you have a specific clinical reason to suspect thyroid disease (myxedema coma, thyroid storm, new atrial fibrillation). Abnormal results in acute illness are almost always sick euthyroid and do not warrant treatment. Recheck 6–8 weeks after recovery if needed.

Pregnancy: Trimester-Specific TSH Ranges

TSH normally drops in the first trimester due to HCG-mediated thyroid stimulation. Using non-pregnant reference ranges will over-diagnose hypothyroidism in early pregnancy:

• First trimester: Upper limit of TSH ~4.0 mIU/L (or ideally population-based trimester-specific ranges from your lab, typically 0.1–2.5)
• Second/third trimester: TSH gradually returns toward non-pregnant range
• Gestational thyrotoxicosis: Suppressed TSH with elevated free T4 in the first trimester, driven by high HCG (hyperemesis gravidarum). TSI-negative. Self-limited. Do NOT treat with antithyroid drugs—it's not Graves'.
• Overt hypothyroidism in pregnancy should be treated aggressively (target TSH <2.5 in first trimester). Levothyroxine dose typically increases 25–50% in pregnancy.

The Pitfalls

• Checking only TSH and missing central hypothyroidism: If a patient has symptoms of hypothyroidism + a pituitary history (surgery, radiation, tumor, postpartum hemorrhage/Sheehan's), check free T4 even if TSH is "normal."
• Biotin interference (from the antibody post): Biotin causes falsely low TSH and falsely high free T4, mimicking hyperthyroidism. Stop biotin supplements 48–72 hours before testing.
• Checking TFTs too soon after dose changes: TSH takes 6–8 weeks to re-equilibrate after a levothyroxine dose change. Don't recheck sooner.
• Ordering total T4 instead of free T4: Total T4 is affected by binding protein changes (pregnancy, estrogen, liver disease). Free T4 is the clinically relevant measurement.
• Over-checking in stable patients: Once hypothyroid patients are stable on levothyroxine, annual TSH is sufficient. More frequent testing creates dose-chasing.
• Treating subclinical hypothyroidism reflexively: TSH 5–10 with normal T4 doesn't always need treatment. Consider symptoms, anti-TPO status, age, cardiovascular risk, and fertility plans.

Pediatric Note

Congenital hypothyroidism is screened on the newborn metabolic panel. A high TSH on newborn screen requires urgent confirmatory testing and treatment—delayed treatment causes irreversible intellectual disability. In children, acquired hypothyroidism (usually Hashimoto's) should be suspected with growth deceleration, delayed puberty, fatigue, and constipation. TSH is the first-line test at any age.

Bottom Line

TSH first. Free T4 if TSH is abnormal. Free T3 only for suppressed TSH with normal T4. Don't test acutely ill patients unless you suspect a thyroid emergency. Use trimester-specific ranges in pregnancy. And stop biotin before testing.

Stay sharp out there.

Vitamin D, B12, and Folate: The Most Over-Ordered and Over-Treated Labs in Primary Care

 

Vitamin D, B12, and Folate: The Most Over-Ordered and Over-Treated Labs in Primary Care

When low B12 is real vs. artifactual, the vitamin D debate that won't die, and why folate deficiency is now almost nonexistent.

These three labs are ordered reflexively on nearly every patient with fatigue, brain fog, or "just to check." And in most cases, the results either don't change management or lead to treatment of a "deficiency" that wasn't real. Let's bring some evidence-based clarity to the most over-ordered panel in primary care.

Vitamin B12

When to Test

Test B12 when there's a clinical reason: macrocytic anemia (MCV >100), peripheral neuropathy, cognitive changes, glossitis, or risk factors for deficiency (strict vegans, pernicious anemia, gastric bypass, metformin use, elderly with poor nutrition, chronic PPI use, Crohn's/celiac affecting the terminal ileum).

The Serum B12 Problem

Serum B12 is a notoriously unreliable test:

• A "low" B12 (200–400 pg/mL) does NOT always mean functional deficiency. Up to 30% of patients with low-normal B12 have no metabolic evidence of deficiency.
• Conversely, some patients with normal serum B12 have functional deficiency at the tissue level.
• Anti-intrinsic factor antibodies can interfere with some B12 assays, causing falsely normal results in pernicious anemia patients who are actually deficient.
• Pregnancy, oral contraceptives, and folate deficiency can all lower serum B12 without true deficiency.

The Confirmatory Test: Methylmalonic Acid (MMA)

MMA is the definitive test for B12 deficiency. B12 is a cofactor for the enzyme that converts methylmalonyl-CoA to succinyl-CoA. When B12 is deficient, MMA accumulates. An elevated MMA confirms functional B12 deficiency regardless of the serum B12 level. Homocysteine is also elevated in B12 deficiency but is less specific (it's also elevated in folate deficiency, hypothyroidism, renal failure, and aging).

The Decision Rule

B12 <200 pg/mL: True deficiency likely. Treat. Check MMA if diagnosis uncertain.
B12 200–400: Gray zone. Check MMA. If MMA elevated, treat. If MMA normal, deficiency is unlikely.
B12 >400: Deficiency excluded in most cases. Don't treat.
Exception: If clinical suspicion is high (neuropathy, macrocytic anemia) regardless of B12 level, check MMA.

Pernicious Anemia Workup

If B12 deficiency is confirmed, determine the cause. Pernicious anemia (autoimmune destruction of parietal cells) is the most important diagnosis to make because it requires lifelong parenteral or high-dose oral B12. Test: anti-intrinsic factor antibodies (highly specific, ~50% sensitive) and anti-parietal cell antibodies (more sensitive but less specific). Pernicious anemia is associated with other autoimmune conditions (autoimmune thyroiditis, vitiligo, type 1 diabetes) and carries an increased risk of gastric carcinoid tumors.

Don't Miss This

B12 deficiency can cause irreversible neurologic damage (subacute combined degeneration of the spinal cord) even without anemia. The neuropathy can precede hematologic changes. If a patient has unexplained neuropathy or gait problems, check B12 and MMA even if the CBC is normal.

Folate

The Short Version: You Almost Never Need to Check It

Since mandatory folic acid fortification of grain products in the US (1998), clinically significant folate deficiency has become rare in the general population. Serum folate is a poor test (it reflects recent dietary intake, not stores) and changes within days of eating folate-rich foods.

When Folate Testing Is Still Relevant

• Macrocytic anemia with normal B12 and normal MMA: Folate deficiency is in the differential (MMA is normal in folate deficiency, which distinguishes it from B12 deficiency; homocysteine is elevated in both).
• Alcohol use disorder: Alcoholism impairs folate absorption and is the most common cause of folate deficiency in developed countries.
• Malabsorption syndromes: Celiac disease, tropical sprue, short bowel syndrome.
• Medications: Methotrexate (folate antagonist), phenytoin, trimethoprim, sulfasalazine.
• Pregnancy: Folate is critical for neural tube closure. However, we supplement with folic acid rather than testing levels.

Clinical Pearl

RBC folate is a better reflection of tissue stores than serum folate (which is too labile). But even RBC folate is now rarely indicated outside of the specific scenarios above. For most primary care patients with fatigue, checking a folate level is not clinically useful.

Danger: Folate Can Mask B12 Deficiency

Giving folate to a patient who actually has B12 deficiency will correct the macrocytic anemia (because folate and B12 share a metabolic pathway for DNA synthesis) but will NOT prevent the neurologic damage of B12 deficiency. Always rule out B12 deficiency before treating macrocytic anemia with folate alone. This is why B12 should be checked first and MMA used to confirm.

Vitamin D

The Ongoing Debate

Vitamin D testing and supplementation is one of the most debated topics in medicine. The evidence has shifted significantly in recent years:

• The USPSTF (2021) found insufficient evidence to recommend screening for vitamin D deficiency in asymptomatic adults.
• The VITAL trial and other large RCTs showed that vitamin D supplementation in unselected adults does not reduce fracture risk, cardiovascular events, or cancer incidence.
• The Endocrine Society (2024) updated guidelines recommending empiric supplementation (1000–2000 IU/day) for certain high-risk groups without routine testing.

The Thresholds

• <12 ng/mL (30 nmol/L): True deficiency. Risk of osteomalacia (adults), rickets (children). Treat.
• 12–20 ng/mL: Insufficiency per some guidelines. Clinical significance debated.
• 20–30 ng/mL: The "gray zone" that generates the most overtesting and overtreatment. The IOM considers 20 ng/mL sufficient for bone health in most people.
• >30 ng/mL: Sufficient by virtually all criteria.
• >50 ng/mL: No proven additional benefit. Risk of toxicity begins above 100 ng/mL.

When to Test Vitamin D

Test When You See

• Osteoporosis or osteomalacia
• Recurrent fractures or unexplained bone pain
• Chronic kidney disease (impaired 1-alpha hydroxylation)
• Malabsorption syndromes (celiac, IBD, short bowel, gastric bypass)
• Medications affecting vitamin D metabolism (anticonvulsants, glucocorticoids, antiretrovirals)
• Hyperparathyroidism workup
• Unexplained hypocalcemia
• Elderly in institutional settings with limited sun exposure

Do NOT Routinely Test

• Asymptomatic adults without risk factors
• "Just to check" as part of a wellness panel
• Patients with fatigue (vitamin D deficiency is very rarely the cause of nonspecific fatigue)

The Pitfalls

• Overtesting asymptomatic patients: Universal vitamin D screening is not recommended and generates a cascade of unnecessary supplementation, retesting, and follow-up.
• Treating "insufficiency" (20–30 ng/mL) aggressively: The evidence for treating levels in this range is weak for most outcomes. Modest supplementation (1000–2000 IU/day) is reasonable for at-risk groups, but high-dose loading protocols for levels of 25 are not evidence-based.
• Checking 1,25-dihydroxyvitamin D instead of 25-hydroxyvitamin D: The correct test for assessing vitamin D status is 25(OH)D. The 1,25(OH)2D test measures the active hormonal form, which is tightly regulated and does NOT reflect stores. It's only indicated in specific scenarios (granulomatous disease, CKD, suspected vitamin D-dependent rickets).
• Vitamin D toxicity from oversupplementation: While rare, it's being seen more often with unregulated high-dose supplementation. Hypercalcemia, nephrocalcinosis, and renal failure can result. Monitor levels if the patient is taking >4000 IU/day.

Quick Reference: When to Test What

Lab	Test When	Don't Test When	Confirm With
B12	Macrocytic anemia, neuropathy, risk factors for deficiency, metformin use	Nonspecific fatigue, "wellness" screening	MMA (elevated = true deficiency)
Folate	Macrocytic anemia with normal B12/MMA, alcoholism, malabsorption, methotrexate use	Routine screening (fortification has made deficiency rare)	RBC folate (better than serum); homocysteine (elevated in both B12 and folate deficiency)
Vitamin D (25-OH)	Osteoporosis, CKD, malabsorption, unexplained bone pain, hyperparathyroidism workup	Asymptomatic adults without risk factors, "just to check," nonspecific fatigue	PTH if hyperparathyroidism suspected; calcium levels

Bottom Line

B12, folate, and vitamin D are important nutrients, but the lab tests for them are overordered, poorly interpreted, and frequently lead to unnecessary treatment. Serum B12 is unreliable in the gray zone—use MMA to confirm. Folate deficiency is now rare and almost never needs checking unless there's macrocytic anemia or specific risk factors. And vitamin D screening in asymptomatic adults is not supported by current evidence—save the test for patients with real risk factors and treat the clinical condition, not the number.

Stay sharp out there.

Tumor Markers in Primary Care: When to Order, When to Step Away, and Why Screening Causes More Harm Than Good

 

Tumor Markers in Primary Care: When to Order, When to Step Away, and Why Screening Causes More Harm Than Good

PSA, CA-125, CEA, AFP—the tests that cause the most unnecessary panic in your practice.

Tumor markers are among the most misused tests in primary care. They get ordered for vague abdominal pain, pelvic discomfort, fatigue, or "just to be thorough"—and then a mildly elevated result triggers imaging, referrals, biopsies, and patient anxiety for a condition that doesn't exist. The core principle: tumor markers are for monitoring known cancers, not for screening asymptomatic patients (with limited exceptions).

The Markers: What They Do and Don't Tell You

Marker	Primary Cancer Association	Non-Cancer Causes of Elevation	Role in Primary Care
PSA	Prostate cancer	BPH, prostatitis, recent ejaculation, bike riding, UTI, age	Screening (shared decision-making for men 55–69); monitoring after treatment
CA-125	Ovarian cancer	Endometriosis, fibroids, PID, pregnancy, menstruation, cirrhosis, CHF, peritonitis, any peritoneal/pleural inflammation	Monitoring known ovarian cancer. NOT for screening pelvic pain.
CEA	Colorectal cancer	Smoking (most common), IBD, pancreatitis, cirrhosis, peptic ulcer, hypothyroidism	Monitoring colorectal cancer post-treatment. NOT for screening.
AFP	Hepatocellular carcinoma, germ cell tumors	Pregnancy, hepatitis, cirrhosis (regenerating nodules)	HCC surveillance in cirrhosis patients (with ultrasound every 6 months). Germ cell tumor monitoring.
CA 19-9	Pancreatic cancer	Biliary obstruction, cholangitis, pancreatitis, cirrhosis. Not expressed in Lewis antigen-negative patients (~5–10%).	Monitoring known pancreatic cancer. NOT for screening abdominal pain.
HCG	Gestational trophoblastic disease, germ cell tumors	Pregnancy (obviously), marijuana use (rarely), pituitary HCG production in postmenopausal women	Monitoring trophoblastic disease and germ cell tumors post-treatment.

The Rules That Prevent Harm

1. CA-125 Is NOT a Screening Test for Ovarian Cancer

This is the most commonly violated rule. CA-125 is elevated in roughly 80% of advanced ovarian cancer but only 50% of early-stage disease. Meanwhile, it's elevated in dozens of benign conditions: endometriosis, fibroids, PID, menstruation, pregnancy, and any cause of peritoneal or pleural inflammation. The USPSTF recommends against screening for ovarian cancer (including CA-125 and transvaginal ultrasound) in average-risk women because screening does not reduce mortality and leads to unnecessary surgeries, some with serious complications.

The Harm

Ordering CA-125 for "pelvic pain" in a premenopausal woman will frequently return a mildly elevated result from endometriosis, a corpus luteum cyst, or menstruation—triggering imaging, surgical consultation, and sometimes unnecessary oophorectomy. Do not order CA-125 as a screening test in average-risk women. It is appropriate for monitoring response in known ovarian cancer or evaluating a suspicious adnexal mass in a postmenopausal woman in conjunction with imaging.

2. PSA: Shared Decision-Making, Not Reflexive Ordering

Per USPSTF (2018, reaffirmed): for men 55–69, PSA screening should be an individual decision made after shared decision-making about benefits and harms. Not recommended for men ≥70 or men with <10-year life expectancy. Key points:

• PSA >4 ng/mL is traditionally considered the threshold, but many cancers occur below 4 and many benign conditions elevate PSA above 4.
• PSA velocity (rate of change) and PSA density (PSA relative to prostate volume) improve specificity.
• For screening, discuss overdiagnosis and overtreatment. Many screen-detected prostate cancers are low-grade and would never cause symptoms or death.

3. CEA Doesn't Screen for Colorectal Cancer

CEA is only useful for monitoring known CRC post-resection (rising levels may indicate recurrence). Smokers commonly have elevated CEA without cancer. It should never be ordered as a CRC screening test—colonoscopy and stool-based tests (FIT, Cologuard) are the appropriate screens.

4. AFP Has a Defined Surveillance Role

AFP plus abdominal ultrasound every 6 months is the recommended HCC surveillance strategy in patients with cirrhosis (any etiology) and chronic hepatitis B without cirrhosis who meet risk criteria. Outside of this specific surveillance context, AFP should not be ordered for vague abdominal symptoms.

The Pitfalls

• Ordering tumor markers for nonspecific symptoms: This creates false-positive results, unnecessary imaging, invasive follow-up procedures, and patient anxiety—without improving outcomes.
• Using tumor markers to diagnose cancer: Tumor markers support diagnosis in the right clinical context but are NEVER diagnostic on their own. Tissue biopsy is required.
• Not knowing the non-cancer causes: Every tumor marker has a long list of benign elevations. If you don't know the list, you'll over-investigate every positive.
• Ordering panels: "Tumor marker panels" that include CA-125, CEA, CA 19-9, AFP, and CA 15-3 together are almost never indicated in primary care. They generate a statistically inevitable false positive and do not improve cancer detection.
• Repeating tumor markers as "follow-up" without oncology guidance: Post-treatment tumor marker surveillance should be directed by the oncology team, not primary care guesswork.

Bottom Line

Tumor markers are monitoring tools, not screening tools (with the narrow exceptions of PSA with shared decision-making and AFP in cirrhosis surveillance). Ordering them for nonspecific symptoms is one of the most reliably harmful testing decisions in primary care. Know what each marker does, know its benign causes, and resist the urge to order a "cancer panel" for reassurance. The reassurance it provides is false, and the anxiety it generates is real.

Stay sharp out there.

HbA1c Pitfalls: When the Number Lies

 

HbA1c Pitfalls: When the Number Lies

Hemoglobinopathies, iron deficiency, CKD, and transfusions all break A1c. Here's when to trust it and when to use alternatives.

HbA1c is the cornerstone of diabetes diagnosis and monitoring. But it measures glycated hemoglobin, which means anything that alters hemoglobin or RBC lifespan will alter the A1c—independent of blood glucose. In your patients with sickle cell trait, iron deficiency, chronic kidney disease, or recent transfusions, the A1c may be telling you a completely different story than what their glucometer shows.

How A1c Works (and Why It Breaks)

A1c measures the percentage of hemoglobin A molecules with glucose attached. It reflects average blood glucose over the preceding 2–3 months (the lifespan of an RBC). This works perfectly when RBC lifespan and hemoglobin structure are normal. When they're not, the test becomes unreliable.

Conditions That Falsely LOWER A1c

These conditions shorten RBC lifespan or increase RBC turnover, giving glucose less time to glycate hemoglobin:

• Hemolytic anemias (autoimmune, G6PD deficiency, hereditary spherocytosis, sickle cell disease)
• Chronic kidney disease (especially on EPO therapy—accelerated erythropoiesis produces younger RBCs)
• Recent blood transfusion (dilutes the patient's glycated hemoglobin with donor RBCs)
• Acute or chronic blood loss (reticulocytosis = younger RBCs)
• Splenomegaly (increased RBC destruction)
• Pregnancy (hemodilution + increased RBC turnover, especially 2nd/3rd trimester)
• Hemoglobin variants: HbS (sickle), HbC, HbE can interfere with some assay methods (though newer methods handle this better)

Clinical Impact

A patient with sickle cell trait and a "normal" A1c of 5.8% may actually have diabetes. A patient on dialysis with an A1c of 6.0% may have average glucoses much higher than 126 mg/dL. If the A1c doesn't match the home glucose readings or clinical picture, suspect interference.

Conditions That Falsely RAISE A1c

These conditions extend RBC lifespan or otherwise increase glycation time:

• Iron deficiency anemia (the most common cause of falsely elevated A1c—iron-deficient RBCs live longer and accumulate more glycation)
• B12/folate deficiency (impaired erythropoiesis = older circulating RBCs)
• Splenectomy (RBCs not being cleared as quickly)
• Alcoholism (forms acetaldehyde-hemoglobin adducts that some assays measure as A1c)
• Chronic opioid use (reported association with falsely elevated A1c)
• Hypertriglyceridemia (can interfere with some assay methods)

The Iron Deficiency Trap

This one trips up NPs constantly. A patient with untreated iron deficiency anemia may have an A1c of 6.8%—technically "diabetic"—that drops to 5.5% after iron repletion. Always check for and correct iron deficiency before diagnosing diabetes based on A1c alone. This is especially important in menstruating women and patients with celiac disease or chronic GI blood loss.

When to Use Alternatives to A1c

Alternative Test	What It Measures	When to Use
Fructosamine	Glycated serum proteins (mainly albumin); reflects 2–3 week average glucose	Hemoglobinopathies, recent transfusion, dialysis, any condition making A1c unreliable. Not useful in hypoalbuminemia (nephrotic syndrome, cirrhosis).
Glycated albumin	Similar to fructosamine; 2–3 week average	Same indications as fructosamine; may be slightly more standardized
CGM (Continuous Glucose Monitoring) data	Real-time and ambulatory glucose profiles; calculates GMI (Glucose Management Indicator)	The gold standard when A1c is unreliable. Provides time in range, variability, and hypoglycemia data. Increasingly accessible.
Fasting glucose / OGTT	Point-in-time or 2-hour post-load glucose	For initial diabetes diagnosis when A1c is suspect; OGTT is the gold standard for gestational diabetes

Ethnic and Genetic Variation

A1c levels can vary by race and ethnicity independent of glucose levels. African American, Hispanic, and Asian patients tend to have A1c values 0.3–0.4% higher than White patients at the same average glucose. This is partially explained by differences in hemoglobin glycation rates and RBC survival. Current diagnostic thresholds (6.5% for diabetes) apply uniformly, but this variation may contribute to diagnostic disparities.

The Pitfalls Summary

• Diagnosing diabetes by A1c alone in a patient with iron deficiency: Correct the iron first, then recheck.
• Trusting A1c in sickle cell disease/trait: Use fructosamine or CGM data instead.
• Monitoring A1c in dialysis patients: A1c underestimates glucose control; use glycated albumin or CGM.
• Post-transfusion A1c: Wait at least 3 months after transfusion for a reliable A1c.
• A1c discordant with home glucose logs: Always investigate—interference from one of the conditions above, or inaccurate glucometer readings, or selective testing by the patient.
• Using A1c for gestational diabetes diagnosis: A1c is NOT recommended for GDM screening. OGTT is the standard.

Bottom Line

A1c is a powerful tool when hemoglobin and RBC lifespan are normal. In patients with hemoglobinopathies, iron deficiency, CKD, hemolysis, or recent transfusion, it lies—sometimes enough to misdiagnose or under-treat diabetes. Know the conditions that raise it falsely (iron deficiency is #1), know the conditions that lower it falsely (hemolysis and CKD), and use fructosamine or CGM when A1c can't be trusted.

Stay sharp out there.