Cardiac Biomarkers: Troponin Trends, BNP Pitfalls, and the Chronic Elevation Problem

 

Cardiac Biomarkers: Troponin Trends, BNP Pitfalls, and the Chronic Elevation Problem

High-sensitivity troponin changed everything. BNP is falsely low in obesity. And a single troponin is almost never enough.

Troponin: The Myocardial Injury Marker

High-Sensitivity Troponin (hs-cTn)

High-sensitivity troponin assays detect far lower concentrations than older assays, enabling faster rule-out of MI but also detecting chronic low-level myocardial injury that was previously invisible. This has created a new problem: chronic troponin elevation without acute MI.

The Trend Is Everything

A single troponin value is not diagnostic. Acute MI shows a rise-and-fall pattern—troponin increases >20% from baseline over 3–6 hours. Chronic elevations (stable, flat values on serial testing) indicate non-ACS myocardial stress. Always order serial troponins at 0 and 3 hours (some protocols use 0 and 1 hour for rapid rule-out with hs-cTn). A flat troponin at two time points effectively rules out acute MI.

Non-ACS Causes of Elevated Troponin

• CKD/ESRD: Chronic low-level elevation from reduced clearance + subclinical ischemia. Present in up to 75% of dialysis patients.
• Heart failure: Myocardial wall stress causes chronic troponin leak.
• Pulmonary embolism: Right ventricular strain elevates troponin (prognostic, not diagnostic for PE).
• Sepsis: Demand ischemia and direct myocardial depression.
• Myocarditis: Often dramatic elevation without coronary obstruction.
• Tachyarrhythmias: Sustained rapid rates cause supply-demand mismatch.
• Takotsubo (stress) cardiomyopathy.
• Cardiac contusion, cardioversion, ablation.
• Extreme exercise: Marathon runners commonly have mildly elevated troponin post-race (resolves in 24–48 hours).

BNP and NT-proBNP: Heart Failure Markers

B-type natriuretic peptide (BNP) and its inactive fragment NT-proBNP are released by cardiomyocytes in response to volume overload and wall stress. They are used for diagnosis and monitoring of heart failure.

Marker	Heart Failure Unlikely	Gray Zone	Heart Failure Likely
BNP	<100 pg/mL	100–400	>400
NT-proBNP	<300 pg/mL	300–age-adjusted threshold	>450 (age <50), >900 (50–75), >1800 (age >75)

The Pitfalls

BNP Is Falsely LOW in Obesity

Adipose tissue expresses natriuretic peptide clearance receptors, causing BNP and NT-proBNP to be falsely low in obese patients. A BMI >35 patient with dyspnea and a BNP of 80 may actually have decompensated heart failure. Use lower thresholds in obese patients (some guidelines suggest halving the cutoff).

• NT-proBNP is renally cleared: Levels are elevated in CKD/ESRD independent of volume status. BNP is less affected by renal function.
• NT-proBNP increases with age: Use age-adjusted thresholds (see table above).
• Atrial fibrillation elevates both BNP and NT-proBNP independent of heart failure.
• Sacubitril/valsartan (Entresto) inhibits BNP degradation, falsely elevating BNP. Monitor with NT-proBNP instead in patients on this medication.
• Both markers are elevated in PE (right heart strain), sepsis, and severe pneumonia—don't assume heart failure without echocardiographic correlation.

Bottom Line

Troponin is a myocardial injury marker, not an MI-specific marker. The trend (rise-and-fall vs. flat) distinguishes acute MI from chronic elevation. BNP/NT-proBNP diagnose and monitor heart failure but are falsely low in obesity and falsely high in CKD, AF, and PE. Always correlate with the clinical picture and use serial measurements.

Stay sharp out there.

Viral Serologies: IgG vs. IgM for EBV, CMV, Parvovirus, and When to Suspect Each Infection

 

Viral Serologies: IgG vs. IgM for EBV, CMV, Parvovirus, and When to Suspect Each Infection

IgM means acute. IgG means past. Except when it doesn't. Here's how to interpret the viral serology panel without getting fooled.

The Universal Principle: IgM vs. IgG

• IgM: The first antibody produced during acute infection. Appears within days to 1–2 weeks of infection. Generally indicates acute or recent infection. Declines over weeks to months.
• IgG: Appears later (2–4 weeks), rises during convalescence, and persists for years to lifetime. Indicates past exposure/immunity.
• IgM positive + IgG negative = early acute infection (seroconversion in progress)
• IgM positive + IgG positive = recent or acute infection (IgG just appearing)
• IgM negative + IgG positive = past infection/immunity
• Both negative = no exposure (susceptible)

The IgM Caveat

IgM is NOT always reliable for timing. False-positive IgM can occur with: polyclonal immune activation (autoimmune diseases, other concurrent infections), rheumatoid factor interference (RF is an IgM that can cross-react in serologic assays), and persistent IgM (some infections like EBV can have detectable IgM for months). Always interpret IgM in clinical context, not as a standalone timestamp.

Virus-by-Virus Guide

EBV (Epstein-Barr Virus) — Infectious Mononucleosis

When to suspect: Adolescents/young adults with fever, severe pharyngitis, posterior cervical lymphadenopathy, fatigue, splenomegaly. Also consider in any age with prolonged febrile illness, atypical lymphocytes on CBC, or hepatitis.

Test	What It Means
VCA IgM (Viral Capsid Antigen)	Positive in acute infection. Appears early, disappears in 4–8 weeks. The best marker for acute mono.
VCA IgG	Appears during acute infection and persists for life. Positive alone = past infection.
EA IgG (Early Antigen)	Appears in acute infection, disappears in 3–6 months. Supports recent infection but present in only ~70% of acute cases.
EBNA IgG (EBV Nuclear Antigen)	Appears 6–12 weeks after onset. Negative in acute mono, positive in past infection. The key test that distinguishes acute from past.
Heterophile antibody (Monospot)	Rapid test. ~85% sensitive in adults/adolescents. Can be negative in children <4 years (up to 50% false-negative rate). If monospot is negative but EBV is suspected, order the full EBV panel.

The Acute EBV Pattern

VCA IgM positive + VCA IgG positive + EA IgG positive + EBNA IgG negative = acute infectious mononucleosis. Once EBNA becomes positive, the infection is past the acute phase. VCA IgG positive + EBNA positive + everything else negative = remote past infection.

Pediatric Pearl

In children <4 years, EBV often presents atypically (rash, irritability, mild URI symptoms) and the monospot has a high false-negative rate. Use the EBV-specific antibody panel instead. Also: EBV + amoxicillin = the classic maculopapular rash (occurs in ~70–100% of mono patients given amoxicillin—not a true drug allergy, but an immune-mediated reaction specific to the EBV context).

CMV (Cytomegalovirus)

When to suspect: Mono-like illness with negative monospot/EBV panel ("heterophile-negative mono"). Immunocompromised patients (transplant, HIV) with end-organ disease. Pregnancy screening when primary CMV is suspected (congenital CMV risk).

• CMV IgM positive: Acute or recent infection (but can persist for months and has false positives from RF).
• CMV IgG positive, IgM negative: Past infection. In immunocompetent patients, this is the most common finding and requires no action.
• CMV IgG avidity: High avidity = infection >3–4 months ago. Low avidity = recent infection (<3–4 months). Essential in pregnancy to time the infection relative to conception.
• CMV PCR (DNA viral load): The test for active CMV disease in immunocompromised patients. Serology is less useful in this population—they may not mount an adequate antibody response.

Pregnancy Pitfall

Primary CMV infection during pregnancy (especially first trimester) carries the highest risk of congenital CMV (hearing loss, microcephaly, intellectual disability). If a pregnant patient has CMV IgM positive, CMV IgG avidity is essential to determine if the infection is recent (low avidity = high risk to fetus) or past (high avidity = lower risk). Do not diagnose primary CMV in pregnancy on IgM alone—IgM can persist and give false-positive "acute" results months after the actual infection.

Parvovirus B19

When to suspect: "Slapped cheek" rash (erythema infectiosum/fifth disease) in children. In adults: symmetric polyarthralgia (especially hands/wrists, mimicking RA), reticulocytopenic anemia (aplastic crisis in sickle cell patients), hydrops fetalis in pregnancy.

• Parvovirus IgM: Appears by day 10–12 of infection, persists for 2–3 months. Indicates acute/recent infection.
• Parvovirus IgG: Appears by week 3, persists for life. Indicates immunity.
• Parvovirus PCR: Detects viral DNA. Essential in immunocompromised patients (who may not produce IgM) and for diagnosing chronic parvovirus infection (persistent anemia in immunosuppressed patients).

Clinical Pearls

• Parvovirus arthritis mimics early RA: Symmetric small joint polyarthralgia in a young woman with recent viral symptoms and a positive parvovirus IgM. Don't start methotrexate—it's self-limited (weeks to months).
• Aplastic crisis in sickle cell: Parvovirus infects erythroid precursors. In patients with chronic hemolysis (sickle cell, spherocytosis), this causes an abrupt reticulocytopenic anemia. Check parvovirus IgM in any sickle cell patient with sudden worsening anemia.
• Pregnancy: Primary parvovirus in the first/second trimester can cause fetal hydrops and death. If exposure is suspected, check IgM and IgG immediately. IgG positive/IgM negative = immune, no risk. IgM positive = refer to MFM urgently for fetal monitoring.

Other Viral Serologies to Know

Virus	When to Suspect	Key Tests	Pitfall
Hepatitis A	Acute hepatitis, travel exposure, foodborne outbreak	HAV IgM (acute), HAV total Ab/IgG (immunity)	Total anti-HAV is positive from past infection OR vaccination—can't distinguish without IgM
Measles	Fever, cough, coryza, conjunctivitis, maculopapular rash, Koplik's spots; unvaccinated or under-vaccinated	Measles IgM (acute, draw at rash onset), measles IgG (immunity check)	IgM may be negative in first 72 hours of rash; repeat if initially negative. Measles IgG confirms vaccination immunity.
Varicella (VZV)	Chickenpox (vesicular rash); immunity check pre-transplant or in healthcare workers	VZV IgG (immunity), VZV IgM (acute—rarely needed, as diagnosis is usually clinical)	VZV IgG confirms immunity from prior infection or vaccination. IgG-negative patients need vaccination (live vaccine—contraindicated in immunosuppressed).
HSV (covered in STI post)	Genital/oral lesions	PCR swab of lesion (gold standard); type-specific IgG for remote diagnosis	Don't screen asymptomatic patients. Low-index-value HSV-2 IgG has high false-positive rate.
HIV (covered in STI post)	Risk factors, acute retroviral syndrome	4th-gen Ag/Ab combo (screen); differentiation assay + RNA (confirm)	Window period 2–4 weeks with 4th-gen. Use RNA for very early suspected infection.
Mumps	Parotitis, orchitis; outbreaks in vaccinated populations	Mumps IgM (acute), PCR (buccal swab preferred)	IgM may be absent in vaccinated individuals with breakthrough mumps; PCR is more reliable.
Rubella	Pregnancy immunity screen; rash illness with arthralgia	Rubella IgG (immunity), IgM (acute); IgG avidity in pregnancy	IgM can persist for months; avidity testing helps time the infection in pregnancy.

When to Use Serology vs. PCR

• Serology (IgG/IgM): Best for immunocompetent patients with intact antibody responses. Tells you about exposure and timing.
• PCR (viral DNA/RNA): Best for immunocompromised patients (may not produce adequate antibodies), for detecting active viral replication, and for confirming acute infection when serology is ambiguous. Essential for CMV and EBV in transplant patients, parvovirus in immunosuppressed, and HSV in active lesions.

The Pitfalls Summary

• IgM can persist for months (especially EBV, CMV)—a positive IgM alone doesn't prove the infection is happening right now.
• Rheumatoid factor causes false-positive IgM in multiple viral assays—if the patient has RA or other conditions with elevated RF, interpret IgM cautiously.
• Monospot is unreliable in young children—use the full EBV panel for kids <4.
• Serology is unreliable in immunocompromised patients—use PCR for CMV, EBV, and parvovirus in transplant recipients and HIV patients.
• Avidity testing is essential in pregnancy for CMV and rubella when IgM is positive—it's the test that determines fetal risk.
• Parvovirus arthritis mimics RA—check parvovirus IgM before starting DMARDs in a patient with acute-onset symmetric polyarthritis.

Bottom Line

Viral serologies follow a consistent IgM (acute) and IgG (past) framework, but the devil is in the details: persistent IgM, RF interference, monospot limitations in children, and the critical role of avidity testing in pregnancy. Know each virus's unique antibody pattern (especially EBV's four-marker panel), use PCR when serology is unreliable, and never start immunosuppressive therapy for "RA" without ruling out parvovirus first.

Stay sharp out there.

Quantitative Immunoglobulins (IgG, IgA, IgM): When to Order, What the Patterns Mean, and the Myeloma Connection

Quantitative Immunoglobulins (IgG, IgA, IgM): When to Order, What the Patterns Mean, and the Myeloma Connection

Recurrent infections, monoclonal spikes, and the difference between too much of one and not enough of everything else.

The Three Immunoglobulins

• IgG (700–1600 mg/dL): The workhorse—75% of serum immunoglobulins. Provides long-term immunity after infection or vaccination. Crosses the placenta (maternal IgG protects the newborn). Low IgG = increased risk of bacterial infections.
• IgA (70–400 mg/dL): Mucosal immunity—found in saliva, tears, respiratory and GI secretions. Selective IgA deficiency is the most common primary immunodeficiency (1 in 400–800). Connects to our celiac post (IgA deficiency causes false-negative tTG-IgA).
• IgM (40–230 mg/dL): The first responder—the initial antibody produced during acute infection. Elevated IgM on infection-specific testing = acute/recent infection. Also the antibody class in Waldenström's macroglobulinemia.

When to Order Quantitative Immunoglobulins

Order When You See

• Recurrent sinopulmonary infections (2+ pneumonias in a year, 4+ ear infections, chronic sinusitis requiring antibiotics) — evaluate for humoral immunodeficiency
• Suspected primary immunodeficiency: CVID (common variable immunodeficiency), selective IgA deficiency, X-linked agammaglobulinemia in boys
• Monoclonal gammopathy workup: SPEP shows an M-spike — quantitative Igs help characterize suppression of uninvolved immunoglobulins (immune paresis)
• Multiple myeloma monitoring: Suppressed uninvolved Igs (immune paresis) = worse prognosis and higher infection risk
• Autoimmune hepatitis evaluation: Elevated IgG is part of the diagnostic criteria (with ANA/SMA/anti-LKM)
• Suspected Waldenström's macroglobulinemia: Markedly elevated IgM with lymphoplasmacytic infiltration
• Before starting rituximab or other B-cell depleting therapy: Baseline Ig levels for monitoring secondary hypogammaglobulinemia
• Celiac workup with negative tTG-IgA: Check total IgA to rule out IgA deficiency

The Patterns

Pattern	IgG	IgA	IgM	Think About
All low (panhypogamma)	↓	↓	↓	CVID, X-linked agammaglobulinemia (boys), secondary causes (rituximab, myeloma treatment, nephrotic syndrome protein loss, chronic lymphocytic leukemia)
Selective IgA deficiency	Normal	↓↓ (<7 mg/dL)	Normal	Most common primary immunodeficiency. Usually asymptomatic. Associated with celiac disease, autoimmune conditions, and anaphylaxis to blood products containing IgA.
One Ig markedly elevated, others suppressed	One ↑↑↑, others ↓			Monoclonal gammopathy / myeloma. The elevated Ig is monoclonal (M-protein). Confirm with SPEP + immunofixation. Suppression of uninvolved Igs = "immune paresis."
All elevated (polyclonal)	↑	↑	↑	Chronic infections (HIV, HCV, TB), autoimmune diseases (SLE, RA, Sjögren's), chronic liver disease (cirrhosis), sarcoidosis
IgG elevated, others normal	↑↑	Normal	Normal	Autoimmune hepatitis (type 1), chronic infections, connective tissue diseases
IgM markedly elevated	Normal/↓	Normal/↓	↑↑↑	Waldenström's macroglobulinemia, primary biliary cholangitis (moderate IgM elevation), acute infection (transient)
IgA elevated	Normal	↑↑	Normal	IgA nephropathy, alcoholic liver disease, celiac disease (paradoxically, some celiac patients have elevated IgA), mucosal infections

The Myeloma Connection: Immune Paresis

Critical Pattern

In multiple myeloma, the malignant plasma cells produce massive amounts of one monoclonal immunoglobulin while suppressing normal immunoglobulin production. This means: IgG myeloma = very high IgG (monoclonal) with very low IgA and IgM. IgA myeloma = very high IgA (monoclonal) with very low IgG and IgM. Light chain myeloma = all immunoglobulins may be low (the paraprotein is free light chains only, not measurable as intact Ig). Immune paresis (suppressed uninvolved Igs) is a hallmark of myeloma and is the reason these patients have severe infection susceptibility. IgG <500 mg/dL in a myeloma patient indicates high infection risk and may warrant immunoglobulin replacement therapy.

CVID: The Primary Immunodeficiency to Know

Common Variable Immunodeficiency is the most clinically significant primary immunodeficiency in adults. Diagnostic criteria: markedly reduced IgG (usually <500) with low IgA and/or IgM, impaired vaccine responses, and exclusion of other causes. Patients present with recurrent sinopulmonary infections, bronchiectasis, autoimmune cytopenias, granulomatous disease, and increased lymphoma risk. Mean age of diagnosis: 20–30s. Many patients are misdiagnosed for years before the Ig levels are checked.

Pediatric Note

Neonates have high IgG (transplacental maternal IgG) that wanes by 3–6 months, creating a physiologic nadir. Transient hypogammaglobulinemia of infancy is a delayed maturation of IgG production that self-resolves by 2–4 years—distinguish from true primary immunodeficiency by the child's ability to make specific antibodies to vaccines. X-linked agammaglobulinemia (Bruton's) presents in boys at 6–12 months when maternal IgG wanes, with all Ig classes virtually absent and no circulating B cells.

Selective IgA Deficiency: The Autoimmune Crossover

IgA deficiency (<7 mg/dL with normal IgG and IgM) connects to multiple posts in this series:

• Celiac disease: IgA deficiency causes false-negative tTG-IgA; always check total IgA with celiac screening
• Autoimmune associations: Higher prevalence of SLE, RA, thyroiditis, and type 1 diabetes
• Transfusion risk: Rare patients develop anti-IgA antibodies, causing anaphylaxis to blood products containing IgA. Use IgA-deficient or washed blood products if anti-IgA antibodies are documented.
• Most IgA-deficient patients are completely asymptomatic and require no treatment.

The Pitfalls

• Don't confuse quantitative Igs with SPEP: Quantitative Igs measure total amounts. SPEP separates proteins by electrophoretic pattern and detects monoclonal spikes. Both are needed for myeloma workup—they answer different questions.
• A "normal" IgG in myeloma patients is misleading: The total IgG may appear normal because the monoclonal IgG is included in the total. Subtract the M-spike from the total IgG to get the uninvolved (polyclonal) IgG, which is often severely depleted.
• Secondary hypogammaglobulinemia is increasingly common: Rituximab, anti-CD38 antibodies (daratumumab), CAR-T therapy, and chronic corticosteroids all cause IgG suppression. Monitor Ig levels in these patients and consider replacement when IgG <400–500 with recurrent infections.
• Age-dependent norms in children: Pediatric Ig levels change dramatically with age. Use age-specific reference ranges. Neonatal IgG is high (maternal); IgM is low (produced by the infant, not transplacental).

Bottom Line

Quantitative immunoglobulins are essential for evaluating recurrent infections, characterizing monoclonal gammopathies, monitoring immunosuppressive therapy, and diagnosing primary immunodeficiencies. One Ig massively elevated with others suppressed = think myeloma. All Igs low = think CVID or secondary immunodeficiency. Selective IgA deficiency = check for celiac and autoimmune associations. And always use age-appropriate norms in children.

Stay sharp out there.

Allergy Testing: Specific IgE, Skin Prick, Component Testing, and Why Large Panels Create More Problems Than They Solve

 

Allergy Testing: Specific IgE, Skin Prick, Component Testing, and Why Large Panels Create More Problems Than They Solve

A positive allergy test doesn't mean allergy. Sensitization ≠ clinical allergy. And shotgun IgE panels are how patients end up on unnecessary elimination diets.

The Fundamental Principle

Sensitization ≠ Clinical Allergy. A positive specific IgE or skin prick test means the patient has IgE antibodies against that allergen (sensitization). It does NOT mean they will have a clinical reaction on exposure. Up to 50–60% of food-specific IgE positives are clinically irrelevant. The test must ALWAYS be interpreted in the context of clinical history.

The Tests

Skin Prick Testing (SPT)

The clinical gold standard for aeroallergen and food allergy testing. Immediate (15–20 minute) wheal-and-flare response. Advantages: rapid, inexpensive, high sensitivity. Limitations: must stop antihistamines 3–7 days prior; cannot perform on patients with severe eczema, dermatographism, or anaphylaxis risk; requires trained personnel.

Serum Specific IgE (sIgE)

Blood test measuring IgE antibodies to specific allergens. Advantages: not affected by antihistamines, safe in any patient, no risk of anaphylaxis during testing. Limitations: measures sensitization, not clinical allergy. Higher values correlate with higher probability of clinical allergy but are not diagnostic on their own.

Total IgE

Often ordered but rarely helpful. Total IgE is elevated in atopic disease, parasitic infections, allergic bronchopulmonary aspergillosis (ABPA), hyper-IgE syndrome, and some immunodeficiencies. It does NOT identify specific allergens. A normal total IgE does NOT exclude allergy. Avoid ordering total IgE as a screening test for allergy.

Component-Resolved Diagnostics (CRD)

The newest and most clinically useful advance. Instead of testing against whole allergen extracts, CRD tests for IgE against specific allergenic proteins (components). This distinguishes true clinical allergy from cross-reactivity. Example: a patient positive for peanut sIgE may be reacting to Ara h 2 (high risk for clinical anaphylaxis) vs. Ara h 8 (a birch pollen cross-reactive protein that rarely causes significant reactions). CRD changes management—the Ara h 2-positive patient needs an EpiPen; the Ara h 8-positive patient may safely eat peanuts.

The Pitfalls

The Large-Panel Trap

Ordering a 50-food IgE panel on a patient with vague GI symptoms will generate multiple false-positive results (given the 50–60% sensitization-without-allergy rate), leading to unnecessary food elimination diets that impair nutrition, increase anxiety, and reduce quality of life—especially in children. Test only for allergens suggested by the clinical history. Targeted testing based on symptoms, timing, and food diary is far more useful than shotgun panels.

• IgG food testing is not validated: IgG to foods represents normal immune exposure, not allergy. Multiple medical societies (AAAI, EAACI, CAS) recommend against IgG food testing. It has no role in allergy diagnosis.
• Negative tests don't always exclude allergy: Skin prick testing and specific IgE have false-negative rates, particularly for drug allergy and some food allergies (e.g., alpha-gal/red meat allergy requires specific testing for galactose-alpha-1,3-galactose IgE).
• Drug allergy testing is limited: Penicillin skin testing is the only well-validated drug allergy test. For most other drugs, diagnosis relies on clinical history and controlled challenge. Specific IgE for drugs is available for a few agents but has limited sensitivity.
• Antihistamines suppress skin testing but not sIgE: If the patient can't stop antihistamines, use serum specific IgE instead of SPT.

Pediatric Note

Food allergy is most common in young children (milk, egg, wheat, soy, peanut, tree nut). Many children outgrow milk, egg, wheat, and soy allergies by school age. Serial specific IgE levels trending downward predict tolerance development. Peanut and tree nut allergies are more likely to persist. The 2017 NIAID guidelines recommend early peanut introduction (4–6 months) in high-risk infants (severe eczema or egg allergy) after appropriate evaluation—this has been shown to prevent peanut allergy development.

When to Refer to Allergist

• History of anaphylaxis
• Suspected food allergy in a child (for supervised oral food challenge)
• Venom allergy (for immunotherapy evaluation)
• Drug allergy testing (penicillin skin test, desensitization protocols)
• Refractory allergic rhinitis or asthma not responding to empiric treatment
• Suspected ABPA (asthma + bronchiectasis + elevated IgE + Aspergillus sensitization)

Bottom Line

Allergy testing detects sensitization, not necessarily clinical allergy. Test based on clinical history, not as a screening panel. Avoid IgG food testing entirely. Use component-resolved diagnostics when available for food allergy risk stratification. And resist the urge to order large IgE panels for nonspecific symptoms—they generate false positives that lead to unnecessary dietary restrictions and patient harm.

Stay sharp out there.

SPEP, UPEP, Immunofixation, and Free Light Chains: The Myeloma Workup NPs Need to Know

 

SPEP, UPEP, Immunofixation, and Free Light Chains: The Myeloma Workup NPs Need to Know

The dipstick misses light chains. SPEP finds the spike. UPEP catches what spills into the urine. And free light chains changed everything.

This post complements the immunoglobulin levels post and the SPEP section from the autoimmune serologic review. When you suspect a monoclonal gammopathy—whether it's MGUS, multiple myeloma, Waldenström's, or amyloidosis—you need to understand the full diagnostic panel: SPEP, UPEP, immunofixation, and serum free light chains.

The Diagnostic Panel

Test	What It Does	When to Order
SPEP (Serum Protein Electrophoresis)	Separates serum proteins by charge. Detects and quantifies an M-spike (monoclonal protein) in the gamma region.	Suspected myeloma, MGUS screening, unexplained elevated total protein, unexplained proteinuria, polyclonal gammopathy evaluation
Immunofixation (IFE)	Identifies the heavy chain (IgG, IgA, IgM) and light chain (kappa or lambda) type of the monoclonal protein.	Confirm and characterize any M-spike seen on SPEP. More sensitive than SPEP for detecting small monoclonal proteins.
Serum Free Light Chains (sFLC)	Measures kappa and lambda free light chains and calculates the kappa/lambda ratio.	Essential for light chain myeloma, AL amyloidosis, and non-secretory myeloma where SPEP may be negative. Also used for MGUS risk stratification and monitoring.
UPEP (Urine Protein Electrophoresis)	Detects monoclonal protein (Bence Jones protein = free light chains) in urine. Requires 24-hour urine collection.	Myeloma workup, AL amyloidosis, monitoring light chain excretion post-treatment. Detects the light chains the dipstick misses.
Urine Immunofixation	Identifies the type of monoclonal protein in urine (kappa vs. lambda).	Confirm any monoclonal band on UPEP

Why the Dipstick Misses Myeloma

Critical Connection to Urinalysis Post

As discussed in the urinalysis post, the urine dipstick detects albumin only. It does NOT detect free light chains (Bence Jones protein). A patient with light chain myeloma can have massive proteinuria on a 24-hour collection with a completely negative dipstick. This is why UPEP or urine immunofixation is essential in the myeloma workup. If you suspect myeloma, never rely on the dipstick to assess proteinuria.

The Screening Panel for Suspected Myeloma

Per current IMWG (International Myeloma Working Group) guidelines, the recommended initial workup when you suspect a plasma cell neoplasm is:

1. SPEP + serum immunofixation
2. Serum free light chains (kappa and lambda with ratio)
3. 24-hour UPEP + urine immunofixation

Together, these three tests detect >99% of myeloma cases. Using SPEP alone misses ~15–20% of cases (light chain only and non-secretory myeloma).

When to Suspect Myeloma in Primary Care

Red Flags That Should Trigger the Workup

• Unexplained anemia (especially normocytic) + elevated total protein or globulin gap
• Bone pain (especially back, ribs) without clear mechanical cause + anemia
• Unexplained renal insufficiency (especially with bland urine sediment and proteinuria)
• Hypercalcemia without obvious cause
• Markedly elevated ESR (>100 mm/hr) with rouleaux on peripheral smear
• Recurrent bacterial infections with low immunoglobulins
• Peripheral neuropathy without other explanation (think AL amyloidosis)
• Incidental M-spike on SPEP ordered for another reason
• Pathologic fractures or lytic bone lesions on imaging

MGUS: The Precursor State

Monoclonal Gammopathy of Undetermined Significance (MGUS) is a pre-malignant condition found in ~3% of adults >50. It progresses to myeloma at ~1% per year. MGUS criteria: M-protein <3 g/dL, bone marrow plasma cells <10%, no end-organ damage (CRAB: Calcium elevation, Renal insufficiency, Anemia, Bone lesions). Risk stratification uses: M-protein size, non-IgG isotype, and abnormal free light chain ratio. Low-risk MGUS can be monitored in primary care with annual SPEP, CBC, creatinine, and calcium.

Free Light Chains: The Game-Changer

Serum free light chains revolutionized myeloma diagnostics. Normal kappa/lambda ratio is approximately 0.26–1.65. An abnormal ratio indicates clonal light chain production. FLC is the most sensitive test for detecting light chain myeloma, AL amyloidosis, and non-secretory myeloma—conditions that SPEP and UPEP may miss. The "involved/uninvolved" FLC ratio is also used for monitoring treatment response and detecting early relapse.

The Pitfalls

• FLC ratio is affected by renal function: In CKD, both kappa and lambda accumulate, and the ratio may be mildly abnormal (kappa/lambda up to 3.1 in renal failure) without a clonal process. Use renal-adjusted reference ranges.
• SPEP can miss small M-proteins: Immunofixation is more sensitive. If SPEP is negative but clinical suspicion is high, the immunofixation and FLC may still be positive.
• Don't confuse polyclonal gammopathy with myeloma: A broad-based elevation in the gamma region = polyclonal (autoimmune disease, chronic infection). A narrow spike = monoclonal (MGUS, myeloma, Waldenström's). Immunofixation distinguishes them definitively.
• Urine collection errors: UPEP requires a complete 24-hour collection. Incomplete collections underestimate proteinuria. Some centers now accept a random urine immunofixation for screening, but 24-hour quantification is still needed for monitoring.
• IgA myeloma is harder to quantify on SPEP: IgA M-proteins migrate in the beta region and may be missed or under-quantified. Quantitative IgA and FLC are important adjuncts for monitoring IgA myeloma.

Bottom Line

The myeloma workup requires three tests: SPEP with immunofixation, serum free light chains, and 24-hour UPEP with urine immunofixation. Using any one alone will miss cases. The urine dipstick is blind to light chains. Free light chains are the most sensitive test for light chain disease. And a monoclonal spike on SPEP in a patient over 50 is MGUS until proven otherwise—but it requires monitoring because 1% per year will progress to myeloma.

Stay sharp out there.