Common Dialysis Labs
Key Takeaways
- Know the target ranges tested on the CCHT: serum potassium 3.5-5.0 mEq/L (predialysis often allowed up to ~5.5), corrected calcium 8.4-9.5 mg/dL, phosphorus 3.5-5.5 mg/dL, albumin >=4.0 g/dL, and hemoglobin held near 10-11 g/dL.
- Adequacy is read from BUN-based math: spKt/V >=1.2 per treatment and URR >=65% are the minimum standards; both rely on correctly timed pre- and post-dialysis BUN samples.
- Potassium is the lab most tied to immediate safety - hyperkalemia (>6.0 mEq/L) can cause lethal arrhythmia, so palpitations, weakness, or a missed treatment with a high recent K+ is escalated at once.
- Calcium, phosphorus, and PTH are read together as the mineral-and-bone (CKD-MBD) picture; the technician reinforces the dietitian's and prescriber's plan but never changes binder or vitamin-D dosing.
- The technician collects, observes, documents, and notifies licensed staff of critical or abnormal values - the technician never diagnoses a result or alters treatment because of one.
Why Labs Matter to the Technician
Laboratory values are how the dialysis team judges five things: adequacy (is enough waste being removed), anemia, mineral and bone balance, nutrition, and immediate safety. Most chronic patients have a fixed monthly lab panel drawn predialysis, plus periodic adequacy, iron, and PTH studies.
The CCHT exam will not ask you to prescribe from a lab. It tests whether you know what a value reflects, which observation matters, and who is notified. That distinction is the recurring theme of the Clinical domain, the largest part of the test.
A single number is rarely the whole story. The team reads trends - a potassium climbing month over month, an albumin slowly falling - alongside symptoms, missed treatments, and access function. A perfect-looking value from a mistimed or recirculated sample is worse than no value, because it hides a real problem.
Think of the panel in three jobs. Safety labs (potassium, calcium) can change today's treatment. Adequacy labs (BUN-based Kt/V and URR) grade whether the dialysis prescription is working. Chronic-management labs (phosphorus, PTH, albumin, hemoglobin, iron studies) drive medication and diet decisions made over weeks. Knowing which bucket a value falls in tells you how urgently to act and whom to involve - the panic value goes to the RN now, the slow trend goes into reinforcement and dietitian referral.
Target Ranges You Must Memorize
Learn each lab's normal range AND the direction that signals danger. The table below is the highest-yield content in this section.
| Lab | Typical target in dialysis | What it reflects | Technician focus |
|---|---|---|---|
| Potassium (K+) | 3.5-5.0 mEq/L (predialysis often <=5.5) | Cardiac/muscle excitability | Report >6.0 or symptoms FAST; high-K foods teaching |
| Sodium (Na+) | 135-145 mEq/L | Fluid/thirst balance | Links to sodium intake and weight gain |
| Calcium (corrected) | 8.4-9.5 mg/dL | Mineral/bone, binder type | Read with phosphorus; reinforce binder timing |
| Phosphorus | 3.5-5.5 mg/dL | Bone, vascular calcification | Binder adherence with meals; diet teaching |
| PTH (intact) | ~2-9x upper normal (per KDOQI) | Parathyroid response to MBD | Reinforce vitamin-D/calcimimetic plan |
| Albumin | >=4.0 g/dL | Nutrition, inflammation | Watch appetite, intake; refer to dietitian |
| Hemoglobin (Hgb) | ~10-11 g/dL (held, not normalized) | Anemia status | Fatigue, pallor, dyspnea, ESA/iron doses |
| Hematocrit (Hct) | ~30-36% | Roughly 3x Hgb | Same as Hgb |
| BUN | Used for Kt/V & URR | Uremic waste, adequacy | Time pre/post samples precisely |
| Bicarbonate (HCO3-) | 22-26 mEq/L | Acid-base balance | Low = acidosis; relates to dialysate bath |
Reading mineral and bone (CKD-MBD) together
- Phosphorus rises because failed kidneys cannot excrete it; high phosphorus pulls calcium from bone and deposits it in vessels.
- Calcium is interpreted with albumin (corrected calcium); low albumin makes total calcium read falsely low.
- PTH climbs when calcium is low and phosphorus is high - secondary hyperparathyroidism. The team treats it with vitamin-D analogs and calcimimetics, not the technician.
Adequacy Math: BUN, Kt/V, and URR
Adequacy answers a single question: did this treatment remove enough small solute? Both standard measures start from BUN (blood urea nitrogen), the lab marker for accumulated waste.
- URR (urea reduction ratio) = (predialysis BUN - postdialysis BUN) / predialysis BUN x 100. The minimum standard is URR >=65%. If predialysis BUN is 60 and post is 18, URR = (60-18)/60 = 70% - adequate.
- Kt/V is a more complete clearance measure (clearance x time, scaled to body water). The standard is single-pool spKt/V >=1.2 per treatment.
Because both depend on BUN, the postdialysis draw technique is critical. A post sample taken without slowing the blood pump pulls in dialysate-cleared blood, reads falsely low, and makes adequacy look better than it is. Conversely, access recirculation lets cleared blood re-enter the needle and distorts results too. The next section covers correct timing; here, the exam point is that bad sampling fakes good numbers.
Creatinine is expected to be high in ESRD and is not a stand-alone score of dialysis success - muscle mass, nutrition, and residual kidney function all move it.
Potassium and Other Safety-Critical Values
Potassium is the lab most tied to immediate danger. Both very high (hyperkalemia, >6.0 mEq/L) and very low (hypokalemia) levels destabilize heart rhythm. A patient who reports palpitations, chest discomfort, muscle weakness, or a missed treatment - especially with a recent high potassium - needs prompt escalation to licensed staff. The technician does not wait for the next routine check.
Hemoglobin guides anemia care. Low values pair with fatigue, pallor, shortness of breath, blood loss, missed ESA doses, or inflammation. Note that Hgb is deliberately held near 10-11 g/dL, not pushed to a non-dialysis "normal" of 14-15 - over-correction raises clotting and cardiovascular risk, which is why the technician never suggests "more ESA."
Albumin below target flags poor nutrition or inflammation and predicts worse outcomes; the response is a dietitian referral, not a technician diet plan. Bicarbonate below ~22 mEq/L signals metabolic acidosis managed through the dialysate bath and prescriber orders.
Worked example. Predialysis labs: K+ 6.4 mEq/L, BUN 58, phosphorus 7.1, Hgb 9.2. The patient mentions skipping last Friday's treatment. The single most urgent item is the potassium of 6.4 plus the missed treatment - report immediately. The phosphorus and Hgb matter but are not minute-to-minute emergencies; you reinforce binder use and document, then notify per policy.
A common exam trap is to label any abnormal value an "emergency." It is not. In ESRD, a high creatinine is expected, a BUN that looks high is normal predialysis, and hemoglobin held at 10.5 is on target, not low. The skill being tested is triage: separate the truly urgent (hyperkalemia, symptomatic anemia, signs of fluid overload) from the chronic (phosphorus, PTH, albumin) so you escalate the right thing at the right speed and reinforce - not panic about - the rest.
A patient's predialysis BUN is 70 mg/dL and the postdialysis BUN is 28 mg/dL. What is the urea reduction ratio (URR), and does it meet the minimum adequacy standard?
Predialysis labs show potassium 6.5 mEq/L. The patient says they feel weak and their heart is 'fluttering.' What is the technician's best first action?
A patient's corrected calcium is 8.8 mg/dL but phosphorus is 7.8 mg/dL and intact PTH is markedly elevated. Which statement best reflects the technician's correct understanding and role?
Why does the dialysis team aim to keep hemoglobin around 10-11 g/dL rather than restoring it to a non-dialysis 'normal' of 14-15 g/dL?