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PA22.3-5 | Laboratory Panel Interpretation — SDL Guide

Learning Objectives

• Interpret a semen analysis panel using WHO criteria and recognise azoospermia, oligospermia and asthenospermia patterns.
• Interpret thyroid function tests (TSH, free T4/T3 ± anti-TPO) and distinguish primary, secondary and subclinical thyroid dysfunction.
• Interpret liver function tests by grouping them into hepatocellular injury, cholestatic and synthetic function markers, and classify jaundice as prehepatic, hepatic or posthepatic.
• Interpret renal function tests (urea, creatinine, eGFR, electrolytes) and distinguish acute kidney injury from chronic kidney disease using prerenal, renal and postrenal frameworks.

INSTRUCTIONS

A clinician who cannot read a lab panel cannot act on it. This module builds the systematic pattern-recognition skill you will use every day in medicine — from the fertility clinic to the ICU. Work through each panel type in order. When you hit a micro-quiz, stop and think before revealing the answer; the reasoning matters more than the result.

References

• Robbins & Kumar: Basic Pathology, 11th ed., Ch 18, 20, 21 (textbook)
• Harsh Mohan: Textbook of Pathology, 8th ed., Ch 23 (textbook)
• WHO Laboratory Manual for Examination of Human Semen, 6th ed. (2021) (guideline)
• EASL Clinical Practice Guidelines on Liver Disease (2022) (guideline)

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Version 2.0 | NMC CBUC 2024

How to Read Any Panel: Universal Principles

Universal Principles for Reading Any Lab Panel

Every lab panel interpretation follows four steps:

1. Check pre-analytical factors first. Haemolysis raises LDH, K⁺ and AST falsely. Lipaemia interferes with bilirubin assays. Semen specimens must be collected after 2–7 days of abstinence; a shorter interval reduces volume and count, a longer interval reduces motility.
2. Compare each value against the reference range provided on the report — ranges vary by method and laboratory. Never memorise absolute numbers without their context.
3. Identify the pattern, not just the single abnormal value. A lone ↑ALT with normal bilirubin, ALP and albumin is very different from ↑ALT + ↑bilirubin + ↓albumin.
4. Generate a differential ordered by probability in the clinical context.

Pre-analytical factors that commonly distort panels:

Factor	Panel affected	Direction of error
Haemolysed sample	LFT (AST, LDH, K⁺)	False ↑
Semen: abstinence <2 d	Semen analysis (count, volume)	False ↓
Semen: abstinence >7 d	Semen analysis (motility)	False ↓
Biotin supplementation	TFT (immunoassay interference)	False ↓ TSH / ↑ T4
Recent heavy meal	Triglycerides, ALP	False ↑

Semen Analysis — WHO 2021 Reference Limits

The WHO 6th edition (2021) provides the following lower reference limits (5th centile of fertile men):

Provided image

Parameter	Lower reference limit
Volume	1.4 mL
Total sperm count	39 × 10⁶/ejaculate
Sperm concentration	16 × 10⁶/mL
Total motility (PR + NP)	42%
Progressive motility (PR)	30%
Morphology (Kruger strict)	4%
Vitality (live spermatozoa)	54%

IMPORTANT NOTE: The WHO 5th edition (2010) figures are still widely quoted in older Indian textbooks. The 6th edition thresholds differ — notably concentration drops from 15 to 16 × 10⁶/mL and normal morphology rises from 4% to 4% (unchanged). Always state which edition you are applying.

Nomenclature for defects:
• Oligospermia — concentration < 16 × 10⁶/mL
• Azoospermia — no spermatozoa in the ejaculate (obstructive vs non-obstructive)
• Asthenospermia — total motility < 42% or progressive motility < 30%
• Teratospermia — morphology < 4% normal forms
• Hypospermia — volume < 1.4 mL
• Oligoasthenoteratospermia (OAT) — combined defect in count + motility + morphology

Worked example — the hook scenario:
- Volume 0.9 mL → below 1.4 mL → hypospermia
- Concentration 8 × 10⁶/mL → below 16 → oligospermia
- Total motility 24% → below 42% → asthenospermia
- Morphology 3% → below 4% → teratospermia
- Combined: OAT syndrome with hypospermia

Possible causes: varicocele (most common reversible cause), partial ejaculatory duct obstruction (explains low volume), or primary testicular failure.

IMPORTANT NOTE: Azoospermia requires two centrifuged semen samples before the diagnosis is confirmed — a single negative spin is not sufficient.

Thyroid Function Tests — Patterns and Interpretation

The standard TFT panel includes: TSH (thyroid-stimulating hormone), free T4 (FT4), free T3 (FT3), and optionally anti-thyroid peroxidase antibodies (anti-TPO Ab).

The hypothalamic–pituitary–thyroid axis operates as a closed-loop feedback system: TSH drives T4/T3 synthesis; rising T4/T3 suppresses TSH. This inverse TSH–T4 relationship is the basis of all TFT interpretation.

Core patterns:

Pattern	TSH	FT4	FT3	Comment
Primary hypothyroidism	↑↑	↓	↓	Thyroid fails → pituitary over-drives
Subclinical hypothyroidism	↑	Normal	Normal	Compensated; anti-TPO predicts progression
Primary hyperthyroidism	↓ (often undetectable)	↑	↑	Excess thyroid hormone suppresses TSH
Subclinical hyperthyroidism	↓	Normal	Normal	Autonomously functioning nodule, early Graves'
Secondary hypothyroidism	↓ or low-normal	↓	↓	Pituitary/hypothalamic disease; TSH does NOT rise despite low T4
Sick euthyroid / non-thyroidal illness	↓ or normal	Normal or ↓	↓↓	Critical illness suppresses T3 conversion

Anti-TPO antibodies:
- Present in ~90% of Hashimoto's thyroiditis (most common cause of primary hypothyroidism in iodine-sufficient populations).
- Present in ~75% of Graves' disease.
- A positive anti-TPO in subclinical hypothyroidism predicts a 4% annual risk of progressing to overt hypothyroidism — this changes the decision to treat.

Worked example:
> TSH 28 mIU/L (ref 0.4–4.0), FT4 6.2 pmol/L (ref 12–22), anti-TPO 890 IU/mL (ref < 35)
> Interpretation: markedly elevated TSH, low FT4 — overt primary hypothyroidism. High anti-TPO confirms autoimmune (Hashimoto's) aetiology. Start levothyroxine.

IMPORTANT NOTE: TSH alone is the best single test for screening. But TSH alone is insufficient when pituitary disease is suspected — you MUST request FT4 as well, because in secondary hypothyroidism TSH is inappropriately low-normal despite low T4.