CPT Code 84443 (TSH): Codes, Denials & ICD-10 Pairs

A denied TSH claim rarely comes from ordering the wrong test. It comes from a coding step that looked routine and got skipped. CPT code 84443 is one of the most-billed lab codes in any practice that touches thyroid care, and that familiarity is exactly why small errors slip through: a diagnosis code too vague to prove medical necessity, a repeat draw that ran past a payer’s frequency limit, a reflex panel billed with the wrong pairing.

This guide breaks down 84443 and the codes it travels with: Free T4, free T3, thyroid antibodies, imaging, biopsy, and the ICD-10 codes that back them up, along with the specific rules that cause denials.

What Does CPT Code 84443 Cover?

CPT code 84443 reports one lab test: Measuring thyroid-stimulating hormone (TSH) in a patient’s blood. It’s the standard first-line test for hypothyroidism, hyperthyroidism, and monitoring thyroid replacement therapy, filed under Pathology and Laboratory, Chemistry Procedures.

A few details that change how the claim gets paid:

• Lab order codes differ; the CPT doesn’t: LabCorp lists TSH under order code 004259; other labs use their own internal numbers. Regardless of which lab runs it, 84443 is the code that goes on the claim.
• Frequency limits are real: Under CMS NCD 190.22, a clinically stable Medicare patient is generally covered for TSH testing twice a year. Many Medicare Administrative Contractors allow up to four times a year, but only when the chart documents a therapy change or new symptoms. A repeat draw without that documentation is a common denial.
• Watch the panel overlap: If a provider orders a general health panel (CPT 80050), TSH is already bundled into it alongside a metabolic panel (80053) and a CBC (85025). Billing 84443 again as a separate line on the same date is an avoidable rejection.

Which Codes Cover Free T4, Free T3 & Related Thyroid Panels?

TSH is the screening test, but a full thyroid workup pulls in several adjacent codes, each billed separately even when a lab groups them under one order name.

• TSH (CPT Code 84443).
• Free T4 (CPT Code 84439).
• Free T3 (CPT Code 84481).
• Total T4 (CPT Code 84436).
• Total T3 (CPT Code 84480).
• TPO Antibodies (CPT Code 86376).
• Parathyroid Hormone (PTH) (CPT Code 83970).

A few pairing rules matter more than the codes themselves:

• Total T4 and Free T4 can’t both be billed: An NCCI edit blocks 84436 and 84439 on the same date for the same patient, and no modifier overrides it. Only 84439 gets paid.
• PTH has a daily cap: Medicare allows one unit of 83970 per day, no matter how many times the level gets checked in that visit.
• TPO antibodies need the right diagnosis: CPT 86376 supports a Hashimoto’s or Graves’ workup and pairs with an autoimmune thyroiditis diagnosis, not a routine screening code.

TSH With Reflex to Free T4: Pros and Cons

Many labs run a reflex protocol: TSH goes first, and if the result falls outside a set range, commonly below roughly 0.30 or above roughly 5.33 µIU/mL, though the exact cutoff is lab-specific, Free T4 gets added automatically, and both codes get billed.

Pros:

• One draw covers the follow-up test automatically, so the patient doesn’t return for a second visit.
• The lab only adds the second charge when the result actually warrants it, which tends to support medical necessity on the claim.

Cons:

• The practice doesn’t control the threshold that triggers the second charge, a borderline result can add a code the ordering physician didn’t specifically request.
• The order documentation needs to match the reflex logic, or the second code can deny even when the first one pays.

What CPT Code Covers a Thyroid Ultrasound?

CPT 76536 covers a thyroid ultrasound. It’s real-time imaging of the soft tissues of the head and neck, thyroid, parathyroid, and parotid glands with images saved to the record.

It’s a single code. Some billing tools list a separate “76537” for a limited or follow-up scan, but that split doesn’t appear in AAPC’s code set or in payer coverage policies; 76536 covers both a full exam and a focused follow-up on a known nodule. Worth double-checking against the current AMA code book before that distinction goes into a claim.

Coverage depends on medical necessity: A palpable mass, an abnormal thyroid lab result, or monitoring a known nodule typically qualify. A scan with no documented reason behind it is a common denial. If the same visit includes an ultrasound-guided biopsy, the guidance component (76942) bills separately from 76536; one covers the diagnostic scan, the other covers the procedure.

What CPT Code Applies to a Thyroid Biopsy?

Two codes cover a thyroid biopsy, and the difference is the needle type. Fine needle aspiration with ultrasound guidance bills as 10005 for the first nodule and 10006 for each additional nodule; a core needle biopsy bills as 60100.

• Guidance billing differs between them: CPT 10005 already includes ultrasound guidance in its own description, so 76942 doesn’t get billed again alongside it. Code 60100 doesn’t include guidance in its descriptor, so 76942 gets added as a separate line.
• FNA usually comes first: A core needle biopsy typically only comes up when an FNA sample comes back non-diagnostic.
• Same-lesion bundling is strict: An FNA code and a core biopsy code generally can’t both be billed for the same nodule at the same visit. If a nodule gets both, check the payer’s NCCI edits before submitting.

Which ICD-10 Codes Pair With TSH and Thyroid Testing?

The right ICD-10 code depends on whether a diagnosis has already been confirmed. R94.6 (abnormal results of thyroid function studies) applies before a specific condition is confirmed. E03.9 (hypothyroidism, unspecified) or E05.90 (hyperthyroidism/thyrotoxicosis, unspecified) apply once the labs and symptoms support an actual diagnosis.

This is the single most common gap coders run into: Billing R94.6 after the chart already documents a confirmed hypothyroidism diagnosis. Once E03.9 applies, R94.6 shouldn’t carry the claim anymore.

Documentation needs to support whichever code gets used. A TSH value alone rarely counts on its own; the note should tie the number to a symptom, a monitoring reason, or a confirmed diagnosis. AAPC’s R94.6 reference is a useful bookmark for this exact distinction, since payers audit it more than most practices expect.

Is There an ICD-10 Code for Thyroid Screening?

Yes, Z13.29 (encounter for screening for other suspected endocrine disorder) applies when a patient has no thyroid symptoms and no prior diagnosis, and the test is ordered as a preventive check.
Z13.29 only fits a true screening visit. If the patient reports fatigue, weight change, or another thyroid-related symptom, that symptom code should lead the claim instead. Some payers process wellness-visit thyroid testing differently from a symptom-driven order, so the diagnosis on file needs to match what actually happened in the visit, not just what got tested.

What Tube Is Used to Draw Blood for a TSH Test?

A gold-top serum separator tube (SST) is the standard collection tube for a TSH draw. Some labs also accept a green-top (lithium heparin) tube when serum isn’t available.

The sample needs to clot, get centrifuged, and stay refrigerated until it reaches the lab. A rejected or hemolyzed specimen means a redraw, which can trigger the frequency-limit issue covered earlier in this guide if it happens more than once in a short window. Getting this step right at the draw station is a quieter way to protect the claim than any coding fix downstream.

Conclusion:

Most of what denies a TSH claim isn’t the test itself. It’s a frequency rule, a bundling edit, or a diagnosis code that doesn’t quite match the chart. None of that needs a coding overhaul to fix; it needs a team that catches the pattern before the claim goes out.

If thyroid panel denials keep showing up in your aging report, HelloMDs denial management team can run a free billing review and show exactly where the pattern starts.