J Clin Med Res

Journal of Clinical Medicine Research, ISSN 1918-3003 print, 1918-3011 online, Open Access

Article copyright, the authors; Journal compilation copyright, J Clin Med Res and Elmer Press Inc

Journal website http://www.jocmr.org

Original Article

Volume 9, Number 1, January 2017, pages 46-57

Serum Free Light Chain Assay and κ/λ Ratio: Performance in Patients With Monoclonal Gammopathy-High False Negative Rate for κ/λ Ratio

**Table 1.** Frequency Distribution of Various Type of Monoclonal Immunoglobulins
Immunoglobulin type	Number of observations	Number of patients
IgG K	923	173
IgG L	543	97
IgA K	305	48
IgA L	180	35
IgM K	88	33
IgM L	37	14
IgD K	10	1
IgD L	26	2
Kappa only	193	40
Lambda only	88	22
Non-secretory	16	3
Total	2,409
Total kappa (including non-secretory)	1,535
Total lambda	874

Table 1. Frequency Distribution of Various Type of Monoclonal Immunoglobulins

Immunoglobulin type

Number of observations

Number of patients

IgG K

923

173

IgG L

543

IgA K

305

IgA L

180

IgM K

IgM L

IgD K

IgD L

Kappa only

193

Lambda only

Non-secretory

Total

2,409

Total kappa (including non-secretory)

1,535

Total lambda

874

**Table 2.** Performance of Electrophoretic Methods and SFLCA κ/λ Ratio With Respect to Level of Concordance With the Established Diagnosis of Monoclonal Gammopathy
Concordance level	SFLCA, N	SFLCA, %	SPEP/SIFE, N	SPEP/SIFE, %
The total 2,409 observations were graded for concordance with the established diagnoses. The results of the electrophoretic methods had significantly higher concordance with the established diagnoses, P < 0.00001. The results of the electrophoretic method had significantly lower discordance rate with a P < 0.00001.
Concordant	1,359	56.41	1,855	77
Non-concordant	971	40.31	540	22.42
Discordant	79	3.28	14	0.58
	P << 0.00001

Table 2. Performance of Electrophoretic Methods and SFLCA κ/λ Ratio With Respect to Level of Concordance With the Established Diagnosis of Monoclonal Gammopathy

Concordance level

SFLCA, N

SFLCA, %

SPEP/SIFE, N

SPEP/SIFE, %

The total 2,409 observations were graded for concordance with the established diagnoses. The results of the electrophoretic methods had significantly higher concordance with the established diagnoses, P < 0.00001. The results of the electrophoretic method had significantly lower discordance rate with a P < 0.00001.

Concordant

1,359

56.41

1,855

Non-concordant

971

40.31

540

22.42

Discordant

3.28

0.58

P << 0.00001

**Table 3.** The Concordance Rates of the Two Methods for Light Chain Specific Results
Concordance level	Kappa (N = 1,535) (including non-secretory)	Lambda (N = 874)
Electrophoretic methods had significantly higher concordance with the established diagnoses for both kappa and lambda light chain monoclonal gammopathies than serum free light chain κ/λ ratio assay results.
Concordant	1010	66.49	1137	74.85	348	39.82	717	82.04
Non-concordant	521	34.3	392	25.81	451	51.6	150	17.16
Discordant	4	0.26	6	0.39	75	8.58	7	0.8
	P < 0.00001 (X² = 26.1)	P << 0.00001 (X² = 344.2)

Table 3. The Concordance Rates of the Two Methods for Light Chain Specific Results

Concordance level

Kappa (N = 1,535) (including non-secretory)

Lambda (N = 874)

SFLC, N

SFLC, %

SIFE, N

SIFE, %

SFLC, N

SFLC, %

SIFE, N

SIFE, %

Electrophoretic methods had significantly higher concordance with the established diagnoses for both kappa and lambda light chain monoclonal gammopathies than serum free light chain κ/λ ratio assay results.

Concordant

1010

66.49

1137

74.85

348

39.82

717

82.04

Non-concordant

521

34.3

392

25.81

451

51.6

150

17.16

Discordant

0.26

0.39

8.58

0.8

P < 0.00001 (X² = 26.1)

P << 0.00001 (X² = 344.2)

**Table 4.** The Samples in Which a Monoclonal Ig Was Detectable by Electrophoretic Methods Were Identified and the False Negative Rate for SFLCA κ/λ Ratio for the Grand Total, Kappa Chain Lesions, Lambda Chain Lesions and Clinical Diagnoses of MGUS, SMM and MM Are Provided
	Number of observations	Electrophoretic positive, N	K/L ratio negative, N	False negative rate for K/L, %
The greater than 55% false negative rate for κ/λ ratio for MGUS patients is noteworthy and argues against a role of SFLCA as a screening tool for monoclonal gammopathy.
Grand total	2,409	1,860	501	26.94
Kappa chain lesions	1,535	1,142	271	23.73
Lambda chain lesions	874	722	230	31.86
MGUS	295	295	163	55.25
SMM	66	60	23	38.33
MM	1,831	1,358	467	34.39

Table 4. The Samples in Which a Monoclonal Ig Was Detectable by Electrophoretic Methods Were Identified and the False Negative Rate for SFLCA κ/λ Ratio for the Grand Total, Kappa Chain Lesions, Lambda Chain Lesions and Clinical Diagnoses of MGUS, SMM and MM Are Provided

Number of observations

Electrophoretic positive, N

K/L ratio negative, N

False negative rate for K/L, %

The greater than 55% false negative rate for κ/λ ratio for MGUS patients is noteworthy and argues against a role of SFLCA as a screening tool for monoclonal gammopathy.

Grand total

2,409

1,860

501

26.94

Kappa chain lesions

1,535

1,142

271

23.73

Lambda chain lesions

874

722

230

31.86

MGUS

295

163

55.25

SMM

38.33

1,831

1,358

467

34.39

**Table 5.** Comparative Results of SFLCA and Electrophoretic Methods at the First Encounter With a Given Patient Are Given Below
Serum free light chain assay at first encounter with a given patient
The false negative κ/λ ratio results are particularly noteworthy in treatment naive MGUS patients at a rate of 67%. The high false negative rate for lesions with lambda light chains, nearly 90%, is in keeping with the high false negative rate for lambda light chain lesions in other settings.
MGUS
K/L ratio +	32	3
K/L ratio -	47	24
Total			66.98
Kappa chain lesions			59.49
Lambda chain lesions			88.89
SMM
K/L ratio +	8	2
K/L ratio -	0	3
Total			23.08
Kappa chain lesions			0
Lambda chain lesions			60
MM
K/L ratio +	139	44
K/L ratio -	33	46
Total			30.15
Kappa chain lesions			19.19
Lambda chain lesions			51.11

Table 5. Comparative Results of SFLCA and Electrophoretic Methods at the First Encounter With a Given Patient Are Given Below

Serum free light chain assay at first encounter with a given patient

Kappa chain lesions

Lambda chain lesions

False Neg, %

The false negative κ/λ ratio results are particularly noteworthy in treatment naive MGUS patients at a rate of 67%. The high false negative rate for lesions with lambda light chains, nearly 90%, is in keeping with the high false negative rate for lambda light chain lesions in other settings.

MGUS

K/L ratio +

K/L ratio -

Total

66.98

Kappa chain lesions

59.49

Lambda chain lesions

88.89

SMM

K/L ratio +

K/L ratio -

Total

23.08

Kappa chain lesions

Lambda chain lesions

K/L ratio +

139

K/L ratio -

Total

30.15

Kappa chain lesions

19.19

Lambda chain lesions

51.11

**Table 6.** Poor Performance of SFLCA κ/λ Ratio in a Patient With IgG Lambda Myeloma
Time of assay	SPEP spike, g/dL	Ig type	Kappa	Lambda	κ/λ ratio
The entries in this table display an example of the poor performance of SFLCA and κ/λ ratio in patients with lambda light chain monoclonal gammopathies. In this case, the SFLCA and κ/λ ratios were consistently negative and discordant despite the fact that each of the 25 samples had a readily detectable monoclonal IgG lambda monoclonal protein. The serum creatinine in this patient was 1.06 mg/dL and renal κ/λ ratio would not have been applicable.
April 2013	1.69	IgG L	13.24	17.97	0.74
December 2012	1.49	IgG L	17.73	12.77	1.39
August 2012	1.44	IgG L	2.59	4.01	0.65
June 2012	1.07	IgG L	3.86	4.17	0.93
December 2011	1.1	IgG L	2.24	3.85	0.58
August 2011	1.32	IgG L	2.78	3.59	0.77
May 2011	1.07	IgG L	1.67	3.51	0.48
April 2011	0.89	IgG L	2.37	5.68	0.42
March 2011	0.95	IgG L	1.56	3.33	0.47
January 2011	0.97	IgG L	1.04	2.71	0.38
November 2010	0.82	IgG L	1.59	2.68	0.59
August 2010	0.66	IgG L	1.01	1.38	0.73
June 2010	0.74	IgG L	1.6	2.56	0.63
May 2010	1.19	IgG L	1.76	5.11	0.34
April 2010	1.2	IgG L	1.82	3.88	0.47
February 2010	1.17	IgG L	1.72	3.89	0.44
December 2009	1.34	IgG L	1.98	2.11	0.94
October 2009	1.18	IgG L	1.9	2.21	0.86
September 2009	1.38	IgG L	2.27	2.26	1.00
August 2009	1.34	IgG L	1.55	2.59	0.60
June 2009	0.77	IgG L	2.03	2.46	0.83
May 2009	0.8	IgG L	2.91	1.5	1.94
March 2009	0.9	IgG L	1.95	1.61	1.21
January 2009	0.7	IgG L	2.36	1.64	1.44
November 2008	0.7	IgG L	2.33	1.65	1.41

Table 6. Poor Performance of SFLCA κ/λ Ratio in a Patient With IgG Lambda Myeloma

Time of assay

SPEP spike, g/dL

Ig type

Kappa

Lambda

κ/λ ratio

The entries in this table display an example of the poor performance of SFLCA and κ/λ ratio in patients with lambda light chain monoclonal gammopathies. In this case, the SFLCA and κ/λ ratios were consistently negative and discordant despite the fact that each of the 25 samples had a readily detectable monoclonal IgG lambda monoclonal protein. The serum creatinine in this patient was 1.06 mg/dL and renal κ/λ ratio would not have been applicable.

April 2013

1.69

IgG L

13.24

17.97

0.74

December 2012

1.49

IgG L

17.73

12.77

1.39

August 2012

1.44

IgG L

2.59

4.01

0.65

June 2012

1.07

IgG L

3.86

4.17

0.93

December 2011

1.1

IgG L

2.24

3.85

0.58

August 2011

1.32

IgG L

2.78

3.59

0.77

May 2011

1.07

IgG L

1.67

3.51

0.48

April 2011

0.89

IgG L

2.37

5.68

0.42

March 2011

0.95

IgG L

1.56

3.33

0.47

January 2011

0.97

IgG L

1.04

2.71

0.38

November 2010

0.82

IgG L

1.59

2.68

0.59

August 2010

0.66

IgG L

1.01

1.38

0.73

June 2010

0.74

IgG L

1.6

2.56

0.63

May 2010

1.19

IgG L

1.76

5.11

0.34

April 2010

1.2

IgG L

1.82

3.88

0.47

February 2010

1.17

IgG L

1.72

3.89

0.44

December 2009

1.34

IgG L

1.98

2.11

0.94

October 2009

1.18

IgG L

1.9

2.21

0.86

September 2009

1.38

IgG L

2.27

2.26

1.00

August 2009

1.34

IgG L

1.55

2.59

0.60

June 2009

0.77

IgG L

2.03

2.46

0.83

May 2009

0.8

IgG L

2.91

1.5

1.94

March 2009

0.9

IgG L

1.95

1.61

1.21

January 2009

0.7

IgG L

2.36

1.64

1.44

November 2008

0.7

IgG L

2.33

1.65

1.41

**Table 7.** The Performance of the Two Methods, i.e., Electrophoretic Methods and SFLCA, for Plasma Cell Myeloma (MM), Smoldering Multiple Myeloma (SMM) and Monoclonal Gammopathy of Undetermined Significance (MGUS) Are Presented
Category	Number	Method	Concordance level for observations only	P value (total concordance)
The concordance of the electrophoretic method results with the established diagnosis was superior to the results of SFLCA in all of the three categories of patients. The level of discordance with the established diagnosis was significantly lower with electrophoretic results than for SFLCA in patients with MM and MGUS. There were insufficient observations in the SMM group for comparison of discordance levels. There was one discordant result, each, with both methods.
MM
Patients	262	SIFE	1,358	468	5
Observations	1,831	SFLC	1,066	711	54	< 0.00001
SMM
Patients	13	SIFE	60	5	1
Observations	66	SFLC	42	23	1	0.00063
MGUS
Patients	76	SIFE	290	5	0
Observations	295	SFLC	132	148	15	< 0.00001

Table 7. The Performance of the Two Methods, i.e., Electrophoretic Methods and SFLCA, for Plasma Cell Myeloma (MM), Smoldering Multiple Myeloma (SMM) and Monoclonal Gammopathy of Undetermined Significance (MGUS) Are Presented

Test method	Total		Kappa		Lambda
Test method	Concordant, N	Concordant, %	Concordant, N	Concordant, %	Concordant, N	Concordant, %
The finding of superiority of the electrophoretic method was applicable in monoclonal gammopathies with both kappa and lambda light chains. As is apparent from the numbers and percentages, the results for lambda light monoclonal gammopathies were far better for electrophoretic methods than for SFLCA κ/λ ratio.
SPEP/SIFE	733	77.73	303	63.66	430	92.08
SFLCA κ/λ ratio	210	22.26	173	36.34	37	7.92
Total	943		476		467
	P < 0.00001		P < 0.00001		P << 0.00001 (X² = 695.5)