Can You Draw Labs From a PICC Line?

Blood can be drawn from a PICC line for most routine laboratory tests, and the results are generally accurate enough to guide clinical decisions. Studies comparing PICC-drawn samples to traditional venipuncture show agreement rates above 90% for the majority of common labs. That said, a few specific tests are more prone to interference when drawn through a PICC, and the technique used to collect the sample matters a great deal. The details are worth knowing whether you are a patient tired of extra needle sticks or a clinician weighing convenience against sample quality.

How Accurate Are PICC-Drawn Lab Results?

The short version is that for most standard blood work, PICC-drawn samples match venipuncture samples closely. A study of patients with sepsis in the emergency department found that accuracy exceeded 90% for nearly every common test, including hemoglobin, white blood cell count, platelets, kidney function markers, electrolytes, blood sugar, prothrombin time, and INR. The accuracy range across those tests was roughly 93% to 99%.¹

Research in hematology patients tells a similar story. When complete blood counts were drawn from PICCs and compared to peripheral venipuncture, a statistically measurable difference showed up for hemoglobin and hematocrit, but the difference was not clinically meaningful. The two methods agreed well enough that treatment decisions would not change based on which collection site was used.²

So if your nurse draws a basic metabolic panel, a CBC, or a standard chemistry set from your PICC, the numbers are overwhelmingly likely to reflect reality. The exceptions are specific enough that they deserve their own discussion.

The Technique That Makes It Work

Pulling blood from a PICC is not as simple as connecting a syringe and drawing. The catheter lumen contains residual fluid, whether that is saline from the last flush, heparin from a lock solution, or remnants of whatever medication was infused most recently. If that residual fluid mixes with your blood sample, the lab results get diluted or chemically altered. Two main techniques exist to deal with this problem.

The traditional approach is the “discard” or “waste” method. The nurse draws a small volume of blood first, throws it away, and then collects the actual sample. The idea is that the first few milliliters clear out whatever was sitting in the catheter. This works, but it means losing blood with every draw, which adds up in patients who get labs pulled multiple times a day.

The alternative is the “push-pull” method, sometimes called “mixing” or blood-sparing sampling. Instead of discarding that first draw, the nurse pushes the blood back into the patient and pulls again, repeating a few times to flush out residual fluid before collecting the real sample. This approach can significantly reduce blood loss from lab draws, which is particularly valuable in intensive care settings where patients may have blood drawn many times daily.³ In pediatric ICUs especially, preventing sampling-related anemia and the need for transfusions is a real concern.

Both methods require a proper flush afterward, typically with normal saline, to keep the catheter patent and clear of residual blood that could clot inside the lumen. If an IV infusion is running through the PICC at the time of the draw, it needs to be paused. Older research established that blood should not be drawn from a line while fluids are actively infusing, since the infusate dilutes the sample and skews results. Stopping the infusion for at least a couple of minutes before collecting the sample is a standard precaution.⁴

Coagulation Tests and Heparin-Locked Lines

Coagulation studies are the test category that raises the most eyebrows when drawn from a PICC. The concern is straightforward: many PICCs are locked with a small amount of heparin between uses to prevent clotting inside the catheter. Heparin is an anticoagulant, and even trace residual amounts in a blood sample can artificially prolong clotting times, making it look like the patient’s blood takes longer to clot than it actually does.

Research has shown this fear is partly overblown, at least when the sample is collected carefully. A study comparing coagulation tests drawn from heparinized PICCs to venipuncture found near-perfect correlations for prothrombin time, partial thromboplastin time, and fibrinogen. Four of the five coagulation tests studied produced accurate results when the researchers followed an evidence-based waste-and-flush protocol. The one test that showed signs of disagreement was INR, though the bias was small.⁵

The sepsis study mentioned earlier found a similar pattern: accuracy for most labs stayed above 93%, but aPTT (activated partial thromboplastin time) dipped to about 86% accuracy, the lowest of any test measured.¹ That 86% number is still useful in many clinical scenarios, but it is a meaningful step down from the near-perfect results seen with chemistry panels and blood counts. If a patient’s treatment hinges on precise aPTT values, such as fine-tuning a heparin drip, many clinicians still prefer a peripheral stick for that specific test.

The practical takeaway: coagulation results from a PICC are not automatically unreliable, but they require careful technique and a clinician who understands the potential for heparin contamination. If the line is saline-locked rather than heparin-locked, the concern drops considerably.

Blood Cultures Are a Different Story

Drawing blood cultures through a catheter, including a PICC, introduces a problem that has nothing to do with sample dilution. It has to do with bacteria. The hub and lumen of any indwelling catheter can harbor microorganisms. When blood passes through that colonized space on its way into a culture bottle, the organisms come along for the ride and grow in the culture medium, producing a false positive.

A large study comparing catheter-drawn blood cultures to venipuncture-drawn cultures found that catheter-drawn samples were equally likely to detect true infections but roughly twice as likely to be contaminated: about 3.8% contamination from catheter draws versus 1.8% from venipuncture.⁶ A contaminated blood culture can trigger unnecessary antibiotic courses, extended hospital stays, and additional testing to figure out whether the result was real or not.

Many hospitals have moved toward policies requiring venipuncture for blood cultures rather than drawing them through central lines. One institution that shifted to venipuncture-only blood culture collection saw contamination rates fall from 1.6% to 0.5%.⁷ That is a substantial drop, and it has real implications for how many patients get treated for infections they do not actually have.

There is a clinical exception. When a central line-associated bloodstream infection is specifically suspected, clinicians often draw cultures from both the PICC and a peripheral site simultaneously. Comparing the time it takes bacteria to grow in each set helps determine whether the catheter itself is the source of infection. In that specific diagnostic scenario, drawing from the PICC is not just acceptable but necessary.

Drug Level Monitoring

Patients on medications like vancomycin or tobramycin need periodic blood draws to ensure drug levels stay in the therapeutic range. Drawing these levels from a PICC raises the worry that drug residue clinging to the catheter wall could falsely elevate the result, especially if the same line was used to administer the medication.

A pediatric study comparing drug concentrations drawn from central venous catheters and peripheral IV sites against venipuncture and fingerstick found substantial agreement for both vancomycin and tobramycin levels. Using a lumen-volume-based flush and waste protocol, the researchers concluded that children with indwelling catheters did not need additional needle sticks to confirm drug concentrations.⁸

That finding is especially welcome in pediatric populations, where every avoided needle stick matters for pain management and cooperation. For adults, the same principle holds: proper flushing and waste technique before collecting drug-level samples yields reliable results. The one caveat is timing. If the same PICC lumen was used to infuse the drug moments earlier, the risk of contamination goes up. Many facilities draw trough levels from the opposite lumen of a multi-lumen PICC or wait a defined interval after infusion ends.

Infection Risk from Repeated PICC Access

Every time a PICC line is accessed, whether for medication administration or blood draws, the system is briefly opened to the outside world. The needleless connector hub at the end of the line is the primary entry point for microorganisms, and research consistently identifies it as a major source of catheter-related bloodstream infections. Studies have found that between a third and nearly half of connector hubs are contaminated at any given time, and compliance with proper disinfection before access can be startlingly low.⁹

A scoping review looking at the relationship between how often central venous catheters are accessed and infection rates found that more frequent access is associated with higher risk of central line-associated bloodstream infection. Importantly, interventions that reduced the number of times a central line was accessed for blood draws effectively lowered those infection rates.¹⁰

This creates a tension. Drawing labs from a PICC spares the patient needle sticks and can be more convenient for nursing staff, but each access event adds a small increment of infection risk. The practical compromise most hospitals have settled on is to consolidate lab draws as much as possible, scrub the connector hub thoroughly before each access (usually with alcohol for at least 15 seconds, though practices vary), and use passive alcohol-impregnated disinfection caps between accesses. Those caps have been associated with large reductions in infection rates, ranging from about half to more than 80% in some studies.⁹

Occlusion and Fibrin Sheath Problems

A PICC line that will not give back blood is one of the more common frustrations in clinical practice. You try to draw labs, and the syringe meets resistance. Sometimes the line flushes fine going in but refuses to let blood come back out. This is often caused by a fibrin sheath, a layer of biological material that forms around the catheter tip over time.

The sheath starts forming within days of catheter placement. Initially it consists of clotted blood and fibrin strands, but over weeks, it matures into a more organized tissue with collagen and other cell types.¹¹ The sheath can act like a one-way valve, allowing fluid to push past it during infusion but collapsing over the catheter tip during aspiration and blocking blood return.

When a PICC develops withdrawal resistance, the typical first-line intervention is instilling a thrombolytic agent like alteplase (or historically urokinase) into the catheter to dissolve the fibrin obstruction.¹² This usually restores function, though the sheath tends to re-form. If withdrawal occlusion becomes a recurring problem, the clinical team may decide the line is no longer suitable for lab draws, even if it still works for infusions.

Complete occlusion, where the line will neither flush nor draw, is less common. A randomized trial comparing PICCs to midline catheters found complete occlusion rates of about 4% to 5% for PICCs, while partial occlusion was under 1%.¹³ PICCs perform well in this regard compared to shorter catheters, which had much higher rates of partial blockage in the same trial.

The Hemolysis Surprise

One concern people raise about drawing blood through any catheter is hemolysis, the rupturing of red blood cells during collection that turns the sample pinkish and ruins certain test results. Intuitively, you might expect that forcing blood through a long, narrow PICC catheter would damage more cells than a simple needle stick. The evidence suggests the opposite.

A study in patients with head and neck cancers compared hemolysis rates between PICC-drawn and venipuncture-drawn samples. Only 1 out of 101 PICC samples showed hemolysis, compared to 11 out of 101 venipuncture samples, a statistically significant difference favoring the PICC.¹⁴ The likely explanation is that venipuncture involves more turbulence and shear stress as blood is pulled through a needle into a vacuum tube, while PICC draws allow a smoother, slower aspiration. For patients who have difficult venous access and frequently get hemolyzed peripheral samples that need to be redrawn, a PICC can actually improve specimen quality.

Saline Versus Heparin Flushing

Whether to lock a PICC with heparin or just use saline between accesses has been debated for years. The answer matters for lab draws because heparin locks create the coagulation-test contamination risk discussed earlier. A systematic review of the evidence found that there is not enough data to conclude heparin flushing is more effective than saline flushing at keeping catheters open.¹⁵

Many hospitals have moved to saline-only flush protocols for PICCs, partly to simplify the workflow, partly to eliminate the risk of heparin-induced thrombocytopenia (a paradoxical immune reaction to heparin), and partly because it makes lab draws from the PICC cleaner. If your PICC is maintained with saline only, the worry about heparin contaminating coagulation samples essentially disappears.

How Common Is PICC Blood Sampling in Practice?

Drawing labs from central lines including PICCs is extremely common, though the exact rates vary by setting. A systematic review spanning multiple sites in the US, Puerto Rico, and Canada found that in adult ICU patients with existing central lines, about 52% of blood culture samples were drawn through those lines. In pediatric ICU practice, the figure was 96%. For hematology-oncology and bone marrow transplant patients, central line blood sampling ran even higher: 64% in adults and 98% in children.¹⁶

The high rates in pediatric and oncology populations make intuitive sense. These patients often have poor peripheral veins, need frequent lab monitoring, and benefit enormously from avoiding repeated needle sticks. Patients themselves tend to prefer having blood drawn from their PICC over getting stuck, though living with a PICC comes with its own inconveniences around dressing changes, movement restrictions, and keeping the site dry.¹⁷

When a Peripheral Stick Is Still the Better Choice

Despite the evidence supporting PICC-drawn labs for most purposes, there are specific situations where a peripheral venipuncture remains preferable:

Blood cultures: The higher contamination rate from catheter-drawn cultures means many facilities mandate peripheral collection to keep false-positive rates low, unless a catheter-related infection is specifically being investigated.
Critical aPTT values: If a patient is on a heparin drip and aPTT is being used to titrate the dose, even a small residual heparin effect from a heparin-locked PICC could throw off the result enough to change management.
Single-lumen PICC with active drug infusion: If the drug was just infused through the only available lumen and there hasn’t been adequate flush time, drawing a drug level from that same lumen risks an artificially high reading.
Withdrawal occlusion: If the PICC will not give blood back despite troubleshooting, a peripheral stick is simply necessary. Forcing aspiration against resistance can damage the catheter.

Outside those scenarios, drawing routine labs from a functioning PICC is well-supported by the evidence and widely practiced. The technique has to be right: adequate waste or push-pull cycling, proper flushing, pausing active infusions, and meticulous hub disinfection. When those steps are followed, the convenience gains for both patients and clinical staff are real and the lab results are trustworthy.

Multi-Lumen PICCs and Lumen Selection

Many PICCs placed in hospitalized patients have two or even three lumens, each functioning as an independent channel into the same vein. This raises a practical question: does it matter which lumen you draw from? The answer is yes, particularly when a medication is being infused through one of the other lumens.

The standard practice is to draw blood from a lumen that is not actively running medication or one that has been adequately flushed and paused. If a patient is receiving total parenteral nutrition through one lumen and an antibiotic through another, the third lumen (or a paused lumen) becomes the draw site. Even with separate lumens, some facilities require pausing all infusions briefly before drawing, because the catheter tips sit in the same vessel within centimeters of each other and cross-contamination of infusate into the draw lumen is at least theoretically possible. The degree to which this matters clinically depends on the specific infusate and the lab being drawn, but playing it safe costs only a minute or two of paused infusion.

Double-lumen PICCs are the most common configuration, and in practice, nurses often designate one lumen for draws and one for infusions to maintain consistency. This habit reduces the odds of accidentally drawing a sample through a lumen that was just used to push a medication bolus.

Pediatric Considerations

Children are the population that benefits most from PICC blood draws. Their veins are smaller and harder to access, they are less cooperative with needle sticks for obvious reasons, and they have less total blood volume, making every unnecessary waste discard more consequential. The push-pull method was developed in large part to address blood-sparing concerns in pediatric ICUs.³

The evidence supporting accuracy in children mirrors the adult data. Drug-level monitoring drawn from central lines in pediatric patients shows strong agreement with peripheral samples when proper flush-and-waste protocols are followed.⁸ The near-universal use of central line blood sampling in pediatric ICUs and oncology units reflects a well-justified consensus that the benefits of avoiding peripheral sticks outweigh the manageable risks of catheter-drawn specimens.

The survey data bear this out: pediatric ICU and oncology settings draw from central lines at rates approaching 96% to 98%, far higher than adult practice.¹⁶ That gap likely reflects not just clinical judgment but also the practical reality that sticking a frightened three-year-old when a perfectly good PICC is already in place is hard to justify unless there is a specific clinical reason to do so.

1
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2
Cancer Nursing. Complete Blood Count Collected Via Venipuncture Versus Peripherally Inserted Central Catheter in Hematological Patients
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PubMed Central. A Standard Push-Pull Protocol for Waste-Free Sampling in the Pediatric Intensive Care Unit
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PubMed. Data regarding blood drawing sites in patients receiving intravenous fluids
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Clinical Nurse Specialist. A Comparison of Coagulation Study Results Between Heparinized Peripherally Inserted Central Catheters and Venipunctures
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PubMed Central. Contamination of catheter-drawn blood cultures
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PubMed. Obtaining blood cultures by venipuncture versus from central lines: impact on blood culture contamination rates and potential effect on central line-associated bloodstream infection reporting
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PubMed. Therapeutic antibiotic serum concentrations by two blood collection methods within the pediatric patient: A comparative effectiveness trial
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PubMed Central. Disinfection of Needleless Connector Hubs: Clinical Evidence Systematic Review
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PubMed. Limiting central venous catheter access for blood sampling and its impact on central line-associated bloodstream infection: A scoping review
11
Radiology Case Reports. Pediatric Fibrin sheath of a peripherally inserted central catheter undepicted with gray-scale (real-time B-mode) ultrasonography: A case report
12
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13
JAMA Network Open. Midline Venous Catheter vs Peripherally Inserted Central Catheter for Intravenous Therapy: A Randomized Clinical Trial
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PubMed. Blood sampling from peripherally inserted central catheter is effective and safe for patients with head and neck cancers
15
PubMed. Heparin flushing and other interventions to maintain patency of central venous catheters: a systematic review
16
PubMed Central. Comparison of Clinical, Economic, and Humanistic Outcomes Between Blood Collection Approaches: A Systematic Literature Review
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Home Health Care Management & Practice. More Benefits Than Problems